<<

Stratigraphic and Paleoecological Controls on Lagerstätten in the Mid-

A dissertation submitted to the Graduate School University of Cincinnati In partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Geology McMicken College of Arts and Sciences 25, 2016

by Matthew Benjamin Vrazo M.S., University of Bristol (UK), 2006 B.S. University of Bristol (UK), 2004

Dissertation Committee

Dr. Carlton E. Brett, Chair Dr. Brooke E. Crowley Dr. Aaron F. Diefendorf Dr. Brenda R. Hunda Dr. Arnold I. Miller

ABSTRACT

The Eurypterida (Arthropoda: ) are unique among chelicerates in having undergone a complete marine-to-freshwater transition during their history. Although the general pattern is well documented, habitats during the peak of the transition during the and Lower have remained unclear. This is due to the co-occurrence of with euryhaline and marine faunas in environments that have been interpreted as hypersaline, and a paucity of detailed bed-level data within eurypterid-bearing occurrences, such within the numerous Lagerstätten of the .

A high-resolution field- and specimen-based analysis was carried out on eurypterid occurrences in Silurian–Lower Devonian-age exposures in the Appalachian basin. Eurypterids in the upper Silurian

Tonoloway Formation of occur in a transgressive succession above microbial structures

(thrombolites) with a marine fauna that suggests near-euhaline conditions. The paucity of occurrences in adjacent hypersaline facies suggests that eurypterids preferentially occupied freshening conditions. A survey of all eurypterid-bearing units in the basin found that the co-occurrence of eurypterids and hypersaline indicators () are common, but only in the northern basin. Here, eurypterid and associated fauna frequently co-occur with disruptive, isolated salt hoppers (pyramidal-shaped pseudomorphs), which suggests intra-sedimentary formation. Thus, eurypterid- associations appear to reflect early-stage diagenesis rather than burial conditions, and it is unlikely that eurypterids inhabited hypersaline conditions. Analysis of eurypterid-bearing strata at the centimeter-scale reveals strong sequence stratigraphic controls on preservation. Eurypterid preservation appears to be principally controlled by water depth in nearshore settings. In carbonate-dominated environments, eurypterids often occur within or above beds containing microbial structures (thrombolites, ) that are interpreted as the flooding surface within small-scale transgressive events. Shallowing-upward successions above these beds, indicated by desiccation features (evaporites, desiccation cracks), are the result of regressions and/or evaporation. A preservational model is proposed whereby eurypterids entered nearshore settings during transgressive freshening events; subsequent hypersalinity and/or dysoxia or

ii anoxia in post-burial sediments following regression was favorable to excellent preservation of . In settings lacking microbial structures or hypersaline indicators, eurypterids occur in similar transgressive successions. Such stratigraphic constraint on eurypterid occurrences permits detailed assessment of morphological variation among equivocal . A combined landmark and semi-landmark-based geometric morphometric analysis of eurypterids from contemporaneous upper Silurian populations indicates that eurypterid morphospecies cannot be distinguished using isolated , unless identifiable macro-scale characters are present. In well-defined species, however, a combined landmark/semi-landmark approach allows regional-scale variance to be quantified.

iii

iv

ACKNOWLEDGEMENTS

There are many people that I need to thank for their contributions to my doctoral journey. Firstly, thank you to my advisor, Carlton E. Brett, for allowing pursue my research interests in both familiar and unfamiliar territory. The guidance I received in the field has been invaluable and will continue with me on future endeavors. I thank Brooke E. Crowley and Aaron F. Diefendorf for introducing me to the world of stable isotopes, willingly answering my many queries once the seed was planted, and ultimately training me to do the job myself. Brenda R. Hunda is thanked for her constant enthusiasm and making a morphometrician out of me. Arnold I. Miller is thanked for his continual support, and helping me think in terms of the big picture. I must also thank the faculty in the Department of Geology at UC, many of whom provided technical, editing, or discursive assistance during the course of my Ph.D. Special thanks goes to Andrew D. Czaja, Warren D. Huff, J. Barry Maynard, and David L. Meyer who kindly provided access to their labs and their technical expertise. Joshua H. Miller is thanked for his input on quantitative analyses and willingness to answer any number of R programming-related questions.

This dissertation is the result of discussions, input, and feedback from many outside the department. Samuel J. Ciurca, Jr. is thanked for generously dispensing his knowledge in the field, and over the course of many emails and phone calls. A significant portion of this dissertation would not have been possible were it not for the samples gathered during his tireless fieldwork over the last 40 . I greatly benefitted from assistance by Dr. Jeffrey M. Trop, both in the field and in during manuscript preparation. Susan Butts and Utrup at the Yale Peabody Museum are thanked for their collections and specimen assistance, which was critical to the completion of this dissertation. John-Paul Zonneveld,

Peter van Roy, and anonymous reviewers read earlier versions of parts of this dissertation and are acknowledged for their helpful criticism and suggestions. Finally, Simon J. Braddy is thanked for setting me down the road of paleoecology and taphonomy that led my continuing interest in this area.

v

Very large thanks goes to my UC graduate colleagues who listened to my endless spiels, offered their own wisdom, provided technical assistance, joined me for a necessary beverage, and ultimately kept me sane over the course of my Ph.D. This includes, but is not limited to Christopher D. Aucoin, Kelsey

M. Feser, Gary J. Motz, Nicholas B. Sullivan, Cameron E. Schwalbach, Janine M. Sparks, James R.

Thomka, Alexander F. Wall, Julia L. Wise, and Andrew A. Zaffos. Thanks goes to Gene Hunt at the

Smithsonian NMNH for offering me a space in which to finish this dissertation, and to Laura C. Soul and

Rachel C. M. Warnock for getting me through the final push.

Funding and support for this dissertation was provided by the Geological Society of America, the

Paleontological Society, the Schuchert and Dunbar Grants in Aid Program (Yale Peabody

Museum), Sigma Xi-University of Cincinnati Chapter, the University of Cincinnati Department of

Geology Caster Fund, the University of Cincinnati Graduate Student Governance Association, the

University of Cincinnati University Research Council, and the University of Cincinnati Graduate School

Dean’s Fellowship.

This dissertation is dedicated to:

My parents, who always supported my interest in natural history and pushed me to go further;

Anna, for her unwavering support (and keeping me on my toes);

Alex (a.k.a., my 6th committee member), whom, without her guidance, patience, and sharp-eyed critiques, this Ph.D. would have never been possible.

vi

TABLE OF CONTENTS

Chapter I: Introduction (pp. 1–5)

Chapter II: A new eurypterid Lagerstätte from the upper Silurian of Pennsylvania (pp. 6–69)

Chapter III: Buried or brined? Eurypterids and evaporites in the Silurian Appalachian basin (pp.

70–118)

Chapter IV: Paleoecological and stratigraphic controls on eurypterid Lagerstätten: a model for preservation in the mid-Paleozoic (pp. 119–173)

Chapter V: Taphonomic bias in taxonomic assignment: a semi-landmark approach to distinguishing species of Silurian eurypterids (pp. 174–230)

Chapter VI: Conclusions (pp. 231–232)

Appendix: Chapter II Supplementary Materials (p. 233–236)

Chapter III Supplementary Materials (p. 237–238)

Chapter V Supplementary Materials (p. 239–252)

vii

Chapter I

INTRODUCTION

The transition of an entire group of organisms from one ecosystem into another is a rare occurrence in the (Vermeij and Dudley 2000). Studies of specific clades that have successfully exploited new ecosystems can provide insight into the causes of these important evolutionary events. The arthropod Chelicerata contains several lineages that have independently made such a transition (Selden and Jeram 1989). These include the

Eurypterida, a predatory and widely distributed aquatic clade that was closely related to and other (Kamenz et al. 2011). Eurypterids originated in open marine environments in the mid- (Lamsdell et al. 2015) and were found in nearshore settings by the Late Ordovician (Young et al. 2007). In the Silurian, eurypterids first appeared in freshwater-influenced environments (Swartz and Swartz 1930; Swartz and Swartz 1931); by the beginning of the , they were restricted entirely to terrestrial, freshwater-dominated settings (Plotnick 1983, 1999; Tetlie 2007). Eurypterids transitioned into a new system only once

(unlike other aquatic chelicerates, e.g., the , Lamsdell 2016), but freshwater taxa were highly successful and survived longer than any marine clade before their extinction in the end-

Permian.

Although the time frame of this emigration is now well defined, the drivers behind it and the reasons for subsequent eurypterid extinctions that began in the end-Silurian remain unresolved (Plotnick, 1999; Lamsdell and Braddy, 2010). Stratigraphic lumping, coarse interpretations of depositional environment, and/or low-resolution bed-level data for many individual eurypterid occurrences during the transitional Silurian–Devonian period (Plotnick

1999) has limited our understanding of eurypterid habits and salinity tolerances. Interpretations

1 of specific salinities (e.g., hyposaline) using faunal evidence are often circumstantial, being generally based on low-diversity marine or euryhaline fauna. Likewise, sedimentary evidence for depositional setting is often lacking (cf. Alling and Briggs 1961), but may include evaporitic features suggestive of conditions in which only the most halotolerant organisms could survive.

Eurypterid-bearing strata during this time also frequently record either variable salinity or hypersaline facies in which individual eurypterid species are confined to thin stratigraphic intervals. Because of the equivocal of these facies, it has been argued that this could either be evidence for narrow salinity tolerances for individual species (cf. Plotnick, 1999), or simply a biased view of generally euryhaline groups captured within narrow taphonomic windows (cf.

Braddy, 2001). The widely accepted “phase” model of habitat niches (i.e., Kjellesvig-Waering

1961) has been recently refuted by Braddy (2001) in favor of a more euryhaline mode of life, but this does not answer the question of specific habitat preference for individual eurypterid taxa at the locality level.

In this dissertation, the question of depositional settings, as they relate to eurypterid habitats in the mid-Paleozoic (and, ultimately, a transition into freshwater), is advanced using a number of field- and specimen-based approaches. A high-resolution methodology is applied throughout in order to overcome previous stratigraphic and taphonomic limitations and biases.

Chapter II focuses on a recently discovered eurypterid Lagerstätte in the upper Silurian

Tonoloway Formation of Pennsylvania. This Lagerstätte yields the first mass assemblage of the common eurypterid away from the northern Appalachian basin and forms the basis for a detailed stratigraphic, taphonomic, and paleoecological analysis of the main site and numerous proximal exposures. Moreover, this site proffers insights into the environmental preferences of eurypterids in nearshore settings and sets the stage for analysis in later chapters.

2

In Chapter III, I consider the likelihood that eurypterids lived in hypersaline or briny environments by performing a survey of eurypterid occurrences in the Silurian units of the

Appalachian basin. Eurypterids are found to occur regularly with evaporites, and specifically salt hoppers (pyramidal halite pseudomorphs) and halite casts/molds, but only in the northern region of the basin. The cross-cutting relationship of the salt hoppers and the substrates in which they are found (including remains of eurypterids and other fauna) indicates that they represent intra- sedimentary formations, i.e., they were not formed at the air-water interface, as is the traditional view for salt hopper development. Thus, these sedimentary features cannot be used to infer the depositional setting for eurypterid occurrences and this helps to constrain eurypterid salinity tolerance. Chapter IV expands on the previous chapter by considering environmental and preservational controls on eurypterid occurrences across the basin using a high-resolution sequence stratigraphic approach. Eurypterids are found to have strong lithological preferences.

However, regardless of the depositional facies, eurypterids and associated fauna typically occur within the same freshening portion of small-scale transgressive successions across a number of defined cycle types. A preservational model that builds on the work in earlier chapters is proposed to explain the biotic and abiotic requirements for the preservation of eurypterid

Lagerstätten in the mid-Paleozoic. Finally, Chapter V considers the question of morphological and phenotypic variations of well-defined eurypterid populations within this refined stratigraphic framework. An integrated landmark/semi-landmark geometric morphometric approach is used for the first time to characterize eurypterid shape in contemporaneous eurypterid populations. The results have implications for the traditional but equivocal use of isolated carapaces as a basis for species in eurypterid systematics.

3

REFERENCES

Alling, H.A., and Briggs, L.I., 1961, Stratigraphy of upper Silurian Cayugan evaporites: AAPG

Bulletin, v. 45, p. 515–547, doi: 10.1306/bc743673-16be-11d7-8645000102c1865d.

Braddy, S.J., 2001, Eurypterid palaeoecology: palaeobiological, ichnological and comparative

evidence for a 'mass-moult-mate' hypothesis: Palaeogeography, Palaeoclimatology,

Palaeoecology, v. 172, p. 115–132.

Kjellesvig-Waering, E.N., 1961, The Silurian Eurypterida of the Welsh Borderland: Journal of

Paleontology, v. 35, p. 789–835, doi: 10.2307/1301214.

Lamsdell, J., Briggs, D., Liu, H., Witzke, B., and Mckay, R., 2015, The oldest described

eurypterid: a giant Middle Ordovician () megalograptid from the Winneshiek

Lagerstatte of Iowa: BMC Evolutionary Biology, v. 15, p. 169.

Lamsdell, J.C., 2016, Horseshoe phylogeny and independent colonizations of :

ecological invasion as a driver for morphological innovation: Palaeontology, v. 59, p.

181–194, doi: 10.1111/pala.12220.

Plotnick, R.E., 1983, Patterns in the of the eurypterids: Unpublished Ph.D. thesis,

Unpublished Ph.D. dissertation, University of Chicago, University of Chicago, 411 p.

Plotnick, R.E., 1999, Habitat of Llandoverian– eurypterids, in Boucot, A.J., and

Lawson, J.D., (eds.), Paleocommunities, A Case Study from the Silurian and Lower

Devonian: Cambridge University Press, Cambridge, p. 106–131.

4

Selden, P.A., and Jeram, A.J., 1989, Palaeophysiology of terrestrialisation in the Chelicerata:

Earth and Environmental Science Transactions of the Royal Society of Edinburgh, v. 80,

p. 303–310, doi: doi:10.1017/S0263593300028741.

Swartz, C.K., and Swartz, F.M., 1930, Age of the Schwangunk conglomerate of eastern New

York: American Journal of Science, v. Series 5 Vol. 20, p. 467–474, doi: 10.2475/ajs.s5-

20.120.467.

Swartz, C.K., and Swartz, F.M., 1931, Early Silurian formations of southeastern Pennsylvania:

Geological Society of America Bulletin, v. 42, p. 621–662, doi: 10.1130/gsab-42-621.

Tetlie, O.E., 2007, Distribution and dispersal history of Eurypterida (Chelicerata):

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 252, p. 557–574, doi:

10.1016/j.palaeo.2007.05.011.

Vermeij, G.J., and Dudley, R., 2000, Why are there so few evolutionary transitions between

aquatic and terrestrial ecosystems?: Biological Journal of the Linnean Society, v. 70, p.

541–554, doi: 10.1111/j.1095-8312.2000.tb00216.x.

Young, G.A., Rudkin, D.M., Dobrzanski, E.P., Robson, S.P., and Nowlan, G.S., 2007,

Exceptionally preserved Late Ordovician biotas from Manitoba, : Geology, v. 35,

p. 883–886, doi: 10.1130/g23947a.1.

5

Chapter II

Vrazo, M.B., Trop, J.M., Brett, C.E., 2014. A new eurypterid Lagerstätte from the upper Silurian

of Pennsylvania. Palaios 29, 431–448.

Matthew B. Vrazo,1 Jeffrey M. Trop,2 and Carlton E. Brett1

1Department of Geology, 500 Geology/Physics Building, University of Cincinnati, Cincinnati,

Ohio 45221-0013 USA

2Department of Geology, O'Leary Center, Bucknell University, Lewisburg, Pennsylvania 17837,

USA

Keywords: Eurypterus, Tonoloway Formation, mass-molt, arthropod taphonomy, trace

6

ABSTRACT

Eurypterids are generally rare in the record, but occasionally occur in abundance. The Eurypterus, in particular, is well known from certain upper Silurian Lagerstätten of the northern Appalachian basin ( and ), but occurs far less frequently in the central and southern Appalachian basin (Pennsylvania, , and West , respectively). The recent discovery of an exceptionally preserved mass assemblage of Eurypterus cf. remipes in the upper Tonoloway Formation (upper Ludlow–Přídolí) of Pennsylvania provides new information on the behavior and habitat of the genus in this region. Eurypterids at this locality are found in thinly laminated, calcareous shale deposited within the lower intertidal to shallow subtidal zone of a coastal mudflat or sabkha. Rare associated fauna of limited diversity, and evaporitic and desiccation features in associated beds, suggest a stressed environment with variable salinity and possible hypoxic conditions. Most eurypterids are disarticulated and fragmentary, but several fully articulated, exceptionally preserved specimens are present. Exoskeletal features and taphonomic indices values indicate a molt, rather than death assemblage, and the presence of arthropod trackways suggests that Eurypterus sp. may have molted en masse in the vicinity of the burial site. Sequence stratigraphic interpretation of the site suggests that preservation of eurypterid remains is the result of occupation of ephemeral environmental (salinity/) conditions during a transgression. The occurrence of this new Lagerstätte within the upper

Silurian succession of the central Appalachians, an interval which had heretofore yielded only rare, fragmentary remains, indicates that eurypterids were more prevalent in this region than previously thought.

7

INTRODUCTION

Eurypterids are extinct, aquatic chelicerates considered to be the sister group to arachnids

(Kamenz et al. 2011; Lamsdell 2013). First appearing in the Middle Ordovician period, initially in open marine settings, they reached peak diversity during the late Silurian before declining and becoming extinct at the end of the , by which time they are found almost entirely within strata representing freshwater environments (Plotnick 1999; Lamsdell and Braddy 2010).

Paleogeographically, eurypterids were widespread. They apparently originated, and were most prolific, on the paleocontinents of Laurentia and , before later expanding into and adjacent areas (Tetlie 2007)(but see Lamsdell et al. 2013, for evidence of a possible origin).

Despite their longevity and wide geographic dispersal, eurypterids are generally rare in the fossil record. Their fragile, non-biomineralized and lightly sclerotized cuticle, and frequent inhabitation of environments not conducive to preservation, e.g., shallow marginal marine or estuarine-type settings, limits the potential for eurypterid occurrences (Kluessendorf 1994). Even where conditions existed to allow for excellent preservation, most eurypterid fossils are disarticulated to some degree (Tetlie et al. 2008). Nevertheless, several eurypterid Konservat-

Lagerstätten are known, such as within the upper Silurian Kokomo of Indiana and the

Bertie Group of the northern Appalachian basin (New York and Ontario) (Kluessendorf 1994).

The dolomitic and chemically precipitated “waterlime” formations of the Bertie Group have produced the most profuse eurypterid assemblages in (Fig. 1), and are known not only for their extremely abundant and often exceptionally preserved eurypterids, but also for other chelicerates including xiphosurans and early scorpions (Plotnick 1999, and references therein). Multiple eurypterid families and genera are found in the Bertie Group, but

8

the genus Eurypterus is by far the most prevalent. For example, within the two most eurypterid- rich units of the Bertie group, the Fiddler’s Green and Williamsville Formations, Eurypterus represents at least 85% of the eurypterid fauna (Kjellesvig-Waering and Heubusch 1962), and, consequently, is the most common in many museum collections.

In the upper Silurian units of the central and southern Appalachian basin, however, eurypterid assemblages reported to date are less abundant and less diverse than those to the north

(Plotnick 1999, and references therein). In these regions, a majority of documented upper

Silurian localities occur in Maryland and (Swartz 1923; Reger 1924; Tilton et al.

1927; Kjellesvig-Waering 1950; Leutze 1960; Kjellesvig-Waering and Leutze 1966), with only two poorly documented examples previously known from Pennsylvania (Schuchert 1903; S.J.

Ciurca, Jr., personal communication 2012) (Fig. 1). Preservation also tends to be poor; specimens are preserved primarily as fragments or in an advanced state of disarticulation, even when found in abundance (e.g., Kjellesvig-Waering and Leutze 1966). Waeringopterus, hughmilleriids and other pterygotoids dominate these eurypterid faunas (Kjellesvig-Waering 1950; Leutze 1960;

Kjellesvig-Waering and Leutze 1966), whereas Eurypterus is strikingly rare. Only one species

(E. flintstonensis) is known from fragments at two localities (Swartz 1923; Tilton et al. 1927;

Kjellesvig-Waering and Leutze 1966), and other Eurypterus remains are only known from isolated fragments (Schuchert 1903; Reger 1924; S.J. Ciurca, Jr., personal communication 2012).

There are two plausible explanations for the dearth of reported eurypterid assemblages from the upper Silurian central and southern Appalachian basin: (1) depositional environments in this region were not conducive to eurypterid habitation and/or preservation, or (2) Pennsylvania, and to a lesser extent Maryland and West Virginia, are undersampled for eurypterids. The genetic similarities of late Silurian depositional environments in the northern Appalachian basin that

9

produce eurypterid Lagerstätten (Clarke and Ruedemann 1912; Ciurca 1973; Kluessendorf 1994) to settings to the south (e.g., Smosna et al. 1977) suggest the latter. In this case, further eurypterid assemblages may yet be prospected in this region (sensu Seilacher et al. 1985).

The recent discovery of a Eurypterus Lagerstätte from the upper Silurian Tonoloway

Formation of Pennsylvania supports the premise that eurypterids are undersampled in the central

Appalachian basin, and offers new insights into the paleoecology and taphonomy of this group.

Using this abundant material, a taphonomic census was carried out (cf. Tetlie and Ciurca 2005), and we discuss possible biostratinomic and taphonomic influences on this assemblage.

Additionally, the integrated sedimentological and paleontological data allow for a paleoenvironmental and paleoecological reconstruction of the depositional environment of the upper Tonoloway Formation within a sequence stratigraphic framework. Within this stratigraphic context, we consider the implications for eurypterid preservation within marginal marine environments in the Appalachian basin.

GEOLOGICAL SETTING AND PALEOECOLOGY

The upper Silurian Tonoloway Formation (upper Ludlow–Přídolí; ~420 Ma) is the uppermost unit in the Salina Group (Cayugan Series) of the central and southern Appalachians and extends from northeastern Pennsylvania into Maryland, Virginia, and West Virginia. This formation lies on the eastern margin of a . Enhanced tectonism in the mid-Silurian

(Wenlock–early Ludlow), sometimes referred to as the Salinic orogeny, produced increased subsidence and the influx of the northwestwardly thinning Bloomsburg clastic wedge, which was up to 1500 m thick (Ettensohn and Brett 2002). By the late Silurian (late Ludlow–Přídolí), however, terrigenous input had been reduced and this, in addition to tectonic quiescence and

10

limited subsidence, allowed for the formation of large areas of muddy carbonate deposition on the eastern and western margins of the basin (Dorobek and Read 1986; Bell and Smosna 1999).

Both the Appalachian and neighboring basins were highly evaporitic (Rickard

1969) due to a generally arid climate and restriction (or closure) of the basin to open oceanic water (Alling and Briggs 1961; Dennison and Head 1975; Smosna et al. 1977). In the

Appalachian basin, these evaporite deposits are represented by the largely subsurface subunits of the Salina Group of western Pennsylvania, southwestern New York, and eastern (Alling and

Briggs 1961). Southeast of this subsurface region, the exposed Wills Creek and Tonoloway formations in the Appalachian fold belt record the marginal-marine and supratidal environments of the basin at this time (Carter 2007).

The restricted circulation of the Appalachian basin during the late Silurian also minimized tidal influence. Based on interpreted water-depth profiles, Smosna and Warshauer (1981) and

Smosna et al. (1999) calculated that the slope of the shoreface along the eastern margin of the

Appalachian basin was very gentle (~0.0006), similar to that of the northern margin at that time

(Belak 1980). They suggested that storm- or wind-driven currents were the main driver of small- scale, tide-like sea-surface fluctuations, rather than strong diurnal or seasonal tides. A number of global eustatic events affected the Appalachian basin during the late Silurian (Johnson et al.

1998), including one event that occurred during deposition of the Tonoloway Formation. The end-Ludlow–Přídolí global transgression event resulted in up to 30 m of sea-level rise prior to a return to lowstand conditions later in the in Přídolí. A later eustatic sea-level rise during the latest

Přídolí–earliest Lochkovian (Dennison and Head 1975) reduced basin-wide salinity and evaporite deposition, and marked a return to continuous carbonate deposition in the eastern and northern regions of the basin (Inners 1981).

11

Stratigraphy and Depositional Environment

The Tonoloway Formation is exposed in central Pennsylvania, western Maryland, eastern

West Virginia, and western Virginia (Heyman 1977). To the west, along the Appalachian basin axis in western West Virginia, Ohio, and western Pennsylvania, this formation is replaced by the upper subunits (D–G) of the subsurface Salina Group; to the north, in north-central Pennsylvania and New York, it is replaced by the Syracuse and Camillus Formations.

Across the Appalachian basin, the Tonoloway Formation has a conformable and gradational contact with the underlying , differing from that unit through a reduction of shale beds (Cotter and Inners 1986), and it shares a disconformable contact with the overlying that can be traced throughout the entire Appalachian basin

(Woodward 1941). The Keyser Formation is a more fossiliferous, argillaceous, and nodular limestone unit compared to the Tonoloway Formation and is thought to represent a return to subtidal, marine conditions capable of supporting reefs (Makurath 1977; Laughrey 1999).

However, despite the appearance of large, in situ reefs within the former, no evidence exists for similar offshore environments within the Tonoloway-equivalent units of western

Pennsylvania (Alling and Briggs 1961; Smosna et al. 1977).

The Tonoloway Formation predominantly displays a peritidal–subtidal carbonate lithofacies succession deposited along a gentle ramp that sloped to the northwest toward the axis of the Appalachian basin (Smosna et al. 1977, 1999), although regional environmental variations and subdivisions exist. The Tonoloway Formation in Maryland and West Virginia has three informal subdivisions (Woodward 1941), whereas the Tonoloway Formation in central

Pennsylvania has two members: an unnamed lower member correlative to most of the lower and middle units of West Virginia, and the overlying and much thinner Turbotville Member (Inners

12

1997); Pennsylvania is missing the slightly deeper water middle unit of West Virginia and

Maryland (Bell and Smosna 1999).

In central Pennsylvania, the lower member is around 180 m thick and is characterized by abundant laminated to thinly bedded, evaporitic, argillaceous, and occasionally mud-cracked micritic dolostone and interbedded calcareous shale (Cotter and Inners 1986; Laughrey 1999).

Other lithologies include evaporites, and minor skeletal wackestone, packstone, rudstone, and grainstone, depending on depositional depth. Repeated occurrences of stromatolites, microbial mat traces, “cryptalgal” laminae, desiccation cracks and evaporite deposits, e.g., gypsum (Cotter and Inners 1986; Bell and Smosna 1999), and halite and calcite pseudomorphs (Ludlum 1959), indicate a restricted and arid lagoonal–tidal mudflat or sabkha-like environment with variable salinity that was regularly subjected to subaerial exposure.

The suprajacent Turbotville Member occupies the uppermost 9–15 m of the Tonoloway

Formation in central Pennsylvania (Inners 1997) and conformably grades from the lower member. It is more fossiliferous, has a greater faunal diversity, and, for the most part, lacks the interbedded calcareous shale of the subjacent lower member. The Turbotville Member also displays less of the characteristic supratidal successions of the lower member and may represent high-intertidal to subtidal conditions consistent with an overall deepening-upward trend (Cotter and Inners 1986).

Cyclicity is prevalent throughout the Tonoloway Formation, including in Pennsylvania

(Tourek 1970). For example, Cotter and Inners (1986) recorded 20+ subtidal–supratidal sabkha- type cycles of varying thickness through a ~150-m-thick exposure of the Tonoloway Formation at Allenport, Pennsylvania. Similar shallowing-upward cycles were also noted by Elick et al.

(2009) from a Pennsylvania quarry roughly 70 miles to the east-northeast.

13

Fauna.—Fossils are typically rare throughout the Tonoloway Formation and many intervals are barren. In those beds containing fossils, faunal diversity is generally low. In the landward inter- and supratidal facies associations that form the bulk of the formation, stromatolites and leperditicopid (Leperditia) dominate, while , including lingulids, gastropods, and fragments of bryozoans appear occasionally (Warshauer and Smosna 1977;

Inners 1997; Bell and Smosna 1999). Within the deeper subtidal deposits that occur throughout the formation, particularly to the southwest, a greater diversity of organisms exists, including bryozoans, various brachiopods, favositid and rugose corals, all of which appear to indicate an occasional return to normal marine (euhaline) conditions (Smosna and Warshauer 1981; Inners

1997; Bell and Smosna 1999).

Locality Description

The primary locality for this study is Winfield Quarry, a recently active and not yet reclaimed limestone quarry in Winfield, Pennsylvania (40°53'55.04"N/76°53'26.13"W; Fig. 2).

Quarrying activity has exposed units from the upper Silurian (Tonoloway Formation, uppermost lower member and Turbotville Member) through Lower Devonian (Old Port Formation,

Ridgeley Member), dipping south-southeast at ~45° (Fig. 3A). Here, the uppermost 9 meters of the Tonoloway Formation are exposed, followed by the overlying Keyser Formation and

Devonian units, which were described by Hess (2008) in a lithostratigraphic, chemostratigraphic, and paleontological study of the exposed outcrop interval.

Lithologically, the Tonoloway Formation at Winfield Quarry is predominantly thin- to medium-bedded micritic limestone, interbedded with thinly bedded and fissile calcareous shale

14

and minor grainstone-to-packstone-to-rudstone units (Figs. 3B–F, 4A–F; see also Appendix,

Chapter II Fig. 1A–X, for additional details). Laminae, possibly of microbial origin, are the most common sedimentary structure (Fig. 4A; Appendix, Chapter II Fig. 1C, I); desiccation cracks

(Fig. 3C; Appendix, Chapter II Fig. 1D–E), syneresis cracks (Fig. 4B), small (<1 cm) evaporitic? calcite-replaced vugs (Appendix, Chapter II Fig. 1B), and shallow, linear, and symmetrical ripple marks (Fig. 4D; Appendix, Chapter II Fig. 1J) are also present, but occur infrequently. Shallow scours occur throughout the section, but are more common in the lower shale units. The beds thicken upward in the section: shale and thin micrite beds are found toward the base of the exposure, and thicker micrite and grainstone beds are found near the top (Fig. 5A).

Eurypterids.—Eurypterids were first discovered at Winfield Quarry in 2008. They are found within two successive calcareous shale packages, either yellowish-weathering, dark chocolate brown or gray in color that occur within a ~ 12-cm-thick interval of the section. The shale packages vary in thickness laterally across strike, but are typically ~6 cm thick and consist of two or three thin laminae of shale; the eurypterids occur on the uppermost laminae in both packages (EB1 and EB2 in Fig. 5A). The yellow coloration of some of the shale laminae is a result of iron weathering within the dolomitic component of the shale (Cotter and Inners 1986) and is distinct from the darker gray and thicker sub- and suprajacent micrite beds. Eurypterids are found both in situ and in the talus at the base of the outcrop. Specimens found in float are easily traced back to their original stratum due to the steep dip-slope of the outcrop and limited exposure of stratigraphic intervals at any one point along strike.

Repeated collecting trips from 2008–2013, during which all visible eurypterid fossils

(including fragments) were systematically collected, have yielded hundreds of well-preserved

15

eurypterid specimens (N = 1756). The layout of the quarry is such that nearly continuous bedding planes of the eurypterid-bearing horizons are exposed on a dip-slope for >700 m along strike. This feature permits exceptional access to the study interval and greatly increases the chances of finding eurypterids both in float and in situ.

The eurypterids are generally preserved as either impressions or compressed carbonized films with sediment infilling that display little relief. A small number of carbonized specimens can be freed from the substrate and retain a slightly three-dimensional topology. Specimen completeness ranges from almost fully articulated examples with most intact (rare), to disarticulated and isolated tergites, appendages, and fragments of cuticle (common); most specimens exhibit some degree of disarticulation (discussed further below) (Fig. 6–7). More fully articulated specimens tend to be isolated, whereas exoskeletal elements and fragments are often clustered together in fossil hashes (Fig. 7B). These hashes are similar in appearance to the eurypterid windrows of New York and Ontario, interpreted by Ciurca (2010) as current- accumulated eurypterid debris deposits. No eurypterid specimens found at Winfield Quarry contain features unequivocally indicative of a carcass such as preserved internal organs or muscle structures (cf. Braddy et al. 1995), but some specimens display features that have been attributed to (see Tetlie et al. 2008, table 1, for features and references, and section 5.1 for disarticulation pattern). These include the frequent attachment of only the first abdominal segment with the carapace (Fig. 6D), separation of the dorsal prosomal unit from the ventral prosomal unit and remaining (Fig. 7B), and suture marks at the anterior end of the prosoma (Fig. 7D).

A detailed morphological and taxonomic treatment is not within the scope of this study, but preliminary comparison of the collected specimens to described taxa from the upper Silurian

16

Appalachian basin suggests that all eurypterids found at Winfield Quarry, with the exception of two specimens (described below), are members of the genus Eurypterus cf. remipes. Eurypterus remipes is known solely from the upper Silurian Fiddler’s Green Formation (upper Přídolí) in

New York and Ontario, a unit younger than the Tonoloway Formation. These specimens will be referred to as Eurypterus sp. herein. Eurypterus sp. is also very similar to E. flintstonensis, which is known from the Tonoloway Formation of Maryland (Swartz 1923) and West Virginia

(Kjellesvig-Waering and Leutze 1966), and the contemporaneous Syracuse Formation of New

York (Leutze 1961). However, E. flintstonensis may be a of E. remipes or E. lacustris

(Kjellesvig-Waering 1958)—themselves considered to be chronospecies (Tetlie et al. 2007), or slight variations of a single species—in which case the age range of E. remipes would be extended into older units. Evidently, a revision of this equivocal taxon is needed before any further assignments can be made.

Regarding the other eurypterid taxa, one specimen is a partial carapace of what appears to be a species within the Dolichopteridae, possibly siluriceps or

Clarkeipterus otisius (J.C. Lamsdell, personal communication 2013) (referred to herein as

?Dolichopterus; Fig. 7C). Dolichopterids are common in the upper Silurian of Baltica

(Kjellesvig-Waering 1961; Manning 1993) and Laurentia (Plotnick 1999, and references therein) where they have been found in association with Eurypterus in New York (e.g., Clarke and

Ruedemann 1912) and West Virginia (Leutze 1960, 1961), but this appears to be the first known occurrence of this family in the Tonoloway Formation. The second specimen is the fixed finger of a pterygotid chelicera, most likely from the genus (S.J. Ciurca, Jr., personal communication 2013) (Fig. 7E). Acutiramus and other pterygotids frequently co-occur with

Eurypterus in the upper Silurian Bertie Group of New York and Ontario (Clarke and Ruedemann

17

1912; Plotnick 1999, and references therein) as well as in various units within the southern

Appalachian basin (Leutze 1960; Kjellesvig-Waering and Leutze 1966). Their presence in the upper Silurian units of Pennsylvania is therefore expected, but this appears to be the first known occurrence of this taxon in the Tonoloway Formation.

Associated Fauna.—Non-eurypterid fossils are of limited diversity and generally sparse at the locality, with the exception of leperditicopids (Leperditia). Leperditia are extremely abundant on some shale layers, including the eurypterid-bearing units, and are found as isolated valves, dense hashes, or accumulations within shallow scours (Appendix, Chapter II Fig. 1L–M, V). Valves are typically unabraded, predominantly convex-up, and range in size from 5–20 mm. Within these leperditicopid assemblages, molds of small, high-spired gastropods (<2 mm; ?Hormotoma) are also present, as are minute, fragmented bryozoans.

Other present within the eurypterid-bearing layers are uncommon and are limited to small (< 4 cm) tabulate corals (Favosites); a single unidentified bivalve preserved only as a dark periostracum (?Modiolopsis); highly compacted and fragmented orthoconic nautiloid ; and a possible juvenile pseudoniscine arthropod (?Pseudoniscus). In thicker argillaceous micrite beds below the eurypterid-bearing interval, in situ mud-draped thrombolites up to 30 cm long and ~8 cm high are present (Fig. 3D–E; Appendix, Chapter II Fig. 1G), as are rare Favosites, abundant Leperditia, and gastropods. Within the thicker micritic wackestone and grainstone beds above the eurypterid-bearing units, the section becomes progressively more fossiliferous and disarticulated cladoporid corals and Leperditia are abundant (Fig. 5A).

Trace Fossils.—Bioturbation and trace fossils are uncommon throughout Tonoloway Formation.

18

At Winfield Quarry, rare, Chondrites-like burrows only occur within the gray micrite beds ~7 m above the eurypterid horizons. Distinctive trace fossils, on the other hand, are common on one of the eurypterid-bearing shale horizons. The trace fossils vary from shallow, linear drag marks and recurrent pairs of curved grooves, to sporadic, chevron- or trifid-shaped impressions, some of which are directional in nature and appear to form symmetrical trackway pairs (Fig. 8). This combination of unique paired markings and their irregular distribution on the bedding surface appears to preclude them from being evaporitic in origin, i.e., early stage halite or gypsum molds, or current- or storm-derived sedimentary structures. Instead, the repeated fine, linear markings and shallow chevron-shaped tracks suggest an arthropod maker. Figure 8D shows some of the sharpest trace impressions. On this slab, several pairs of diametrically opposed chevron- shaped marks and a trifurcated drag mark occur alongside a longer, medial drag mark. These resemble chelicerate arthropod tracks such as the “simple tracks” and single chela tracks of either

Paramphibius, an ichnogenus revised and ascribed by Caster (1938, fig. 1B; plate 1, fig. 3) to a

Devonian xiphosuran similar to Protolimulus, or individual tracks within the putative eurypterid ichnogenus Palmichnites cf. antarcticum (Braddy and Milner 1998), further suggesting an arthropod tracemaker.

Other Eurypterid-Producing Localities.—To determine whether Winfield Quarry is a singular and areally restricted eurypterid-producing locality, or represents part of a larger regional assemblage, 13 additional localities with exposures of the Tonoloway Formation in the vicinity of Winfield, Pennsylvania were scouted (see Appendix, Chapter II Table 1, for locality and reference details). Of these, the only localities known to have previously yielded eurypterids are

Selinsgrove Junction and Atkinson Mills (Fig. 1). At Selinsgrove Junction, the uppermost

19

Tonoloway and Keyser Formations are exposed for approximately one mile along an active railway on the east side of the Susquehanna River. A single Eurypterus fragment was found here by Schuchert (1903), but the exact location is unknown and the specimen is apparently lost. No additional material was found by us during recent fieldwork there.

The Atkinson Mills locality (40°27'13.58"N/77°49'33.72"W) is a small exposure of the

Tonoloway Formation (upper Turbotville Member) through Keyser Formation that dips to the east-northeast on the south side of the intersection of US-22 E/US-522 N and T361 (Cookson

Lane). Eurypterid specimens were collected here in the 1970s by Samuel J. Ciurca, Jr. from two horizons (S.J. Ciurca, Jr., personal communication 2012; Fig. 5B) and consist of several complete and partial carapaces of Eurypterus cf. remipes (M.B. Vrazo, personal observations

2012; Fig. 9A, B). These are now part of the Ciurca Collection at the Yale Peabody Museum of

Natural History (YPM 215872–215894). During recent fieldwork at Atkinson Mills, the current authors obtained an isolated paddle and partial tergite from float (Fig. 9C, D). These specimens share the same lithology (calcisiltite) and distinctive color (yellowish-orange) of the lower

Ciurca eurypterid horizon (~240 cm from base of outcrop) (Fig. 5B) and most likely originated from there.

The eurypterid-bearing units at Atkinson Mills differ from those of Winfield Quarry in terms of lithology and color. Stratigraphically, however, the eurypterid-bearing beds occur within nearly identical vertical successions. At both localities, the eurypterid-horizons are preceded by a succession of beds containing chert, desiccation cracks, syneresis cracks, and thrombolites, respectively. Additionally, both exposures generally thicken upward and become predominantly micritic toward the overlying Keyser Formation. These stratigraphic similarities suggest that these are coeval units and that the chert, thrombolites, and desiccation features may be useful as

20

marker beds for tracing the eurypterid horizons elsewhere.

POPULATION DISTRIBUTION AND TAPHONOMIC CENSUS

Materials and Methods

The size-frequency distribution of the eurypterid population at Winfield Quarry was determined using carapace length (a proxy for body length; Vrazo and Braddy 2011) measured digitally with ImageJ (Rasband 2011; accuracy = ±0.2 mm [n = 10]). Because the prosoma is capable of being deformed and distorted both before and after burial (Tollerton 1989), significantly altered specimens were not measured; however, these are generally rare. Accurate recording of dorsal or ventral way-up orientation was not possible due to a large proportion of the material occurring as float.

Although some specimens from Winfield Quarry display features consistent with molted remains (see above), such features are lacking on most specimens. In the absence of features diagnostic of either molts or carcasses, taphonomic indices can be used to quantitatively distinguish between a molt or death assemblage at the population level (Tetlie et al. 2008). To aide in determining whether the eurypterid fossils at Winfield Quarry represent a death or molt assemblage, a taphonomic census based on specimen completeness was carried out. All specimens examined as part of this census were found either in situ or in float directly beneath the only known eurypterid-bearing horizons at this locality. Eurypterid specimen completeness was quantified using the Eurypterid Completeness Index (ECI), Carapace-Segment-Attachment-

Index (CSAI), and Carapace- Attachment Index (CAAI) of Tetlie and Ciurca (2005).

These indices, developed originally to perform a taphonomic census on the comprehensive

Ciurca Collection at the Yale Peabody Museum, are based on the degree of disarticulation of

21

individual specimens and can be averaged to evaluate the overall completeness of an assemblage.

A similar taphonomic census was carried out by Vrazo and Braddy (2011, table 2) in an attempt to quantify the disarticulation pathway of assemblages of E. remipes and E. lacustris from the

Fiddlers Green and Williamsville Formations, respectively, of the Bertie Group of New York and

Ontario.

The ECI quantifies exoskeletal completeness by dividing a complete eurypterid into 26 individual elements (see Tetlie et al. 2008, p. 185, for specifics). Each complete element is coded as 1; partial elements are coded as 0.5, and isolated, unidentifiable fragments are coded as 0.1.

For example, a fully articulated specimen would have a total score of 26, whereas an isolated would have a score of one. The CSAI and CAAS, on the other hand, are only based on the number of attached segments (≤12, ignoring the equivocal reduced 1st opisthosomal segment/microtergite [see Dunlop and Webster 1999]) or prosomal appendages (≤12) attached to a carapace, respectively. Using either the CSAI or CAAS, a fully articulated specimen would have a total score of 12. A bias of the ECI is that mostly or fully articulated specimens will outweigh partial or fragmented specimens. All material from a given locality must therefore be collected and encoded to avoid collector bias. Limitations of this index are that exoskeletal fragments are often difficult to discern, especially when combined as a hash with other fragments, and such quantification can be time consuming and inaccurate. The CSAI and CAAI, on the other hand, ignore all fragmented and non-identifiable material, and may be more effective where collector bias is present, but will only be useful when articulated prosomas with attached segments or appendages are present.

The Ciurca Collection at the Yale Peabody Museum is considered qualitatively to lack significant collector bias (O.E. Tetlie, personal communication 2012); nevertheless, we decided

22

to test for effects of potential collector bias. In comparing the sample size of individual localities against completeness index values (as a metric of potential bias), we found no significant correlation between the ECI, CSAI, and CAAI values calculated by Tetlie et al. (2008, table 6) for eight localities and their respective sample size (Pearson’s; df = 6, p > 0.05). This indicates that the completeness index values obtained from these eight localities are independent of sample size, and can be utilized elsewhere as unbiased baseline indicators of death versus molt assemblages, and the depositional condition (i.e., high or low energy) of the latter (Tetlie et al.

2008).

Results

Based on the measured length of 50 complete, or nearly complete, and undistorted carapaces, the eurypterids at Winfield Quarry represent a normally distributed (p > 0.05, one- tailed) population. The carapace lengths range in size from juvenile to fully grown adult (~4–40 mm; mean: 20.15 mm; median: 22 mm; SD: 6.76) (Fig. 10), with most specimens falling within what might be considered the young adult size (~22–28 mm). Vrazo and Braddy (2011) noted the subjective nature of previously assigned instar size classes, e.g., larvae, juvenile, adult, but a general growth stage of Eurypterus can be inferred not only from its overall size, but also the proportional size of swimming paddles compared to total length, and the gross morphology of its carapace. Juveniles have a quadrate carapace and rounded anterior margin, whereas adults have a more trapezoidal carapace and a flattened anterior margin. Additionally, the eyes become relatively smaller and move posteriorly on the carapace with growth (see Andrews et al. 1974, and Brower and Veinus 1978, for ontogenetic examples). The size-frequency distribution of the eurypterid specimens at Winfield Quarry is similar to the distributions found by others for late

23

Silurian Eurypterus populations within the northern Appalachian basin (Andrews et al. 1974;

Vrazo and Braddy 2011), with the caveat that the sample size of carapaces from Winfield Quarry is roughly one-third the sample size available to the latter two studies.

The results of the taphonomic census indicate that most specimens are disarticulated to some degree. Of the 59 with an attached prosoma collected, only 13 are fully articulated with the maximum number of tergites (12), and just over half of those (7) also had an attached whole or partial telson. The largest number of articulated prosomal appendages on any individual from the assemblage was 6.5 (out of 12). It should be noted, however, that only one chelicera was identified within the entire assemblage, and thus the presence/absence of had virtually no influence on the census results discussed below.

The ECI value calculated for the Eurypterus sp. assemblage from Winfield Quarry is 1.06

(N = 1756; range: 0.1–21.5). This value represents 4.07% of a fully articulated exoskeleton and the average percent of specimen completeness from this locality. This value is lower than all ECI values calculated by Tetlie et al. (2008, table 6) excepting one. However, with the exception of the Kokomo, Indiana, Wabash Formation assemblage, which is considered to be a death assemblage (Clarke and Ruedemann 1912; Tetlie et al. 2008), most values for the remaining localities are low (e.g., 1–2), and were interpreted as indicative of a molt assemblage by Tetlie et al. (2008).

The values calculated for the CSAI and CAAI yielded respective values of 4.81 (n = 62) and 2.10 (n = 28). These values are comparable to those calculated by Tetlie et al. (2008) for E. remipes from the Ellicott Creek Breccia Member (Fiddler’s Green Formation) of the R.E. Law

Quarry, Ontario (CSAI = 5.40; CAAI = 1.60; Tetlie et al. 2008, table 6), considered to be a molt assemblage. The Ellicott Creek Breccia Member is thought to represent a shallow sub- to

24

intertidal setting (Brett 1989; Vrazo et al. 2013), similar to the lower and upper units of the

Tonoloway Formation. The ECI value calculated for the Ellicott Creek Breccia Member assemblage (3.56), on the other hand, is much greater than that calculated for the Winfield

Quarry assemblage.

DISCUSSION

Paleoenvironmental Reconstruction

The fine-grained, clay-rich micrite and calcareous shale units, low-amplitude symmetrical ripple marks, microbial mounds, thin shale laminae, desiccation cracks, small-scale evaporitic structures (e.g., vugs), and overall paucity of bioturbation and current-generated structures suggest that the exposure of the Tonoloway Formation at Winfield Quarry principally represents a shallow, restricted, and low-energy intertidal to shallow subtidal environment such as a mudflat or sabkha with variable salinity. This is consistent with previous interpretations of the upper

Tonoloway Formation (Tourek 1970; Smosna et al. 1977; Smosna and Warshauer 1981; Cotter and Inners 1986; Inners 1997; Bell and Smosna 1999; Hess 2008; Elick et al. 2009).

Within this broader paleoenvironmental characterization, three distinct depositional facies associations can be identified. The desiccation cracks and vugs near the base of the outcrop (Fig.

3B–F) are consistent with deposition within a high intertidal to supratidal setting. The suprajacent thrombolite bed records an initial deepening (transgression). The thinly laminated eurypterid- and leperditicopid-bearing calcareous shale units then mark the beginning of the next facies association (Fig. 4A–C), interpreted as being deposited in a lower intertidal to shallow subtidal setting. This facies association is followed lastly by thicker, ripple-marked, and increasingly fossiliferous micrite, packstone, and rudstone units (Fig. 4D–F), which we interpret

25

as being deposited in a subtidal setting. Combined, these three facies associations record a transgressive, upward-deepening sequence that begins with the initial flooding surface at the transition of the thrombolite bed, continues within the eurypterid-bearing shale beds, and culminates with subtidal facies associations that precede the less restricted and predominantly subtidal Keyser Formation.

The faunal diversity of Winfield Quarry supports these environmental interpretations and is comparable to that seen at other localities. Descriptions of the inferred tidal mudflat facies associations of the Tonoloway Formation in West Virginia (Smosna et al. 1977; Smosna and

Warshauer 1981) and Pennsylvania (Bell and Smosna 1999) all note the same assemblage of leperditicopids, gastropods, and bryozoan fragments that is seen in the eurypterid-bearing beds at

Winfield Quarry. This fauna is also broadly similar to that of the slightly older Syracuse

Formation of New York, which has been interpreted as a shallow, highly restricted tidal setting occasionally inundated with evaporitic brines (Leutze 1961). A greater diversity of eurypterids, other arthropods, and molluscs is known from the latter unit compared to the Tonoloway

Formation, but, as at Winfield Quarry, eurypterids (including Eurypterus) and abundant leperditicopids are the predominant taxa. Farther afield, in what are interpreted as intertidal flat deposits of the upper Silurian (Ludlow) Leopold Formation of the Canadian Arctic, Jones and

Dixon (1974) and Jones and Kjellesvig-Waering (1985) describe a faunal assemblage strikingly similar to that of Winfield Quarry. This assemblage includes eurypterids (Eurypterus, syn.

Baltoeurypterus; Tetlie 2006), gastropods (Hormotoma), , and leperditicopids

(Leperditia), and less common corals (including Favosites), bryozoans, and orthoconic nautiloids, as well as brachiopods.

26

Paleosalinity.—The frequent occurrence of Ordovician and Silurian eurypterids in restricted marginal settings that may have fluctuated between brackish, normal marine, and hypersaline conditions, and the resultant difficulty in assigning a preferred habitat or salinity to individual groups has long been known to paleontologists. Within eurypterid-bearing units in the upper

Silurian northern Appalachian basin, for example, Alling and Briggs (1961) and Leutze (1961) both noted the difficulty in determining salinity at the bed level due to the frequent lack of fossil or sedimentary evidence, in spite of the traditional interpretation of many eurypterid-bearing formations in this region as predominantly hypersaline (Braddy 2001).

As to the north, the prevailing sedimentological features (e.g., desiccation cracks, evaporitic vugs, syneresis cracks) throughout much of the Tonoloway Formation in

Pennsylvania, including those found at Winfield Quarry and Atkinson Mills, indicate that salinity in this environment was variable, and undoubtedly hypersaline at times. Furthermore, the

Tonoloway Formation passes laterally into the Syracuse and Camillus Formations, both of which contain thick evaporite deposits of halite and gypsum. And yet, within the eurypterid-bearing beds at Winfield Quarry and Atkinson Mills, limited faunal diversity and a lack of bioturbation only imply abnormal conditions, but do not directly suggest either elevated or brackish salinity levels.

The fauna offer some secondary evidence for paleosalinity and environmental conditions.

Vannier et al. (2001) suggested that a monospecific distribution of leperditicopids on bedding surfaces (such as at Winfield Quarry) was an indication of periods of growth in low-energy environments (e.g., a tidal flat) where sediment influx was limited. Likewise, Warshauer and

Smosna (1977) and Smosna and Warshauer (1981) interpreted the Leperditia-dominated communities within the lower and upper units of the Tonoloway Formation of West Virginia as

27

an indication of low-energy, stressed, and possibly hypersaline environments that were frequently subjected to subaerial exposure. The abundance of leperditicopids across multiple horizons at Winfield Quarry seems to indicate that these beds were deposited under similarly stressed conditions with variable or hypersalinity.

Eurypterus has been variously reported from units interpreted as brackish–freshwater

(e.g., Kjellesvig-Waering 1950) and highly hypersaline (e.g., the Ellicott Creek Breccia and others, see Ciurca 2011). However, we believe that sedimentary indicators of hypersalinity (e.g., salt hoppers) in the latter example may have been formed within the sediment post-burial (i.e., they are early diagenetic features), rather than coeval with the eurypterids and cannot be taken as direct evidence that eurypterids lived under hypersaline conditions. Other limitations on possible eurypterid salinity tolerance can be gained from comparisons to modern marine chelicerates, e.g., horseshoe . The latter are euryhaline and can tolerate elevated salinity levels (Ehlinger and

Tankersley 2004), but have a preferred salinity range well beneath that required for evaporite formation (i.e., brines > 80 ppt). When taking into consideration the stratigraphic position of the eurypterid beds at Winfield Quarry and Atkinson Mills—above supratidal strata containing desiccation features and below a subtidal succession containing more diverse marine taxa—it seems plausible that salinity was euhaline, or somewhat elevated at the time of their burial, but probably not hypersaline.

Variable salinity may not have been the only stressor in these environments. Dysoxic or anoxic conditions, frequently associated with the low-energy, hypersaline environments of other

Silurian and Ordovician eurypterid Lagerstätte (Kluessendorf 1994; Young et al. 2007), may have played a role in reducing faunal diversity while also increasing the likelihood of soft tissue preservation (see below). Although there is no direct evidence for dysoxia/anoxia at Winfield

28

Quarry or Atkinson Mills, the extremely gentle slope of the Tonoloway Formation’s carbonate ramp (which probably extended horizontally for tens of kilometers; Bell and Smosna 1999), combined with irregular tides, minimal oceanic influx, and an arid climate would have occasionally led to stagnant bodies of water where only highly tolerant leperditicods may have been able to survive. These stressed conditions in the shallowest part of the mudflat may have been punctuated by periods of reduced salinity/increased oxygenation due to storms/rain, freshwater runoff, or minor transgressions (cf. Leutze 1961), and it was probably during these intermittent periods of freshening that eurypterids (and associated eurytopic fauna) preferentially occupied these settings (see below for further discussion).

Taphonomy.—The abundant, often well-preserved eurypterids at Winfield Quarry (and by extension, Atkinson Mills) suggest either a molt or death assemblage. Evidence for eurypterid mortalities is traditionally limited and equivocal (e.g., Sarle 1903; Størmer 1955; Heubusch

1962; Andrews et al. 1974; Copeland and Bolton 1985; Braddy et al. 1995; Tetlie et al. 2008) and often difficult to prove. Unequivocal death assemblages, such as in the Silurian-age Kokomo

Limestone (Indiana) (Clarke and Ruedemann 1912; Tetlie et al. 2008) and Pentland Hills

() (Anderson et al. 2007; Lamsdell 2011) Lagerstätten are rare in the fossil record.

Conversely, eurypterid molt assemblages occur more commonly (although, notably, at nowhere near the frequency of other contemporaneous arthropods such as ), as do the morphological features used to identify molted remains (Tetlie et al. 2008, table 1). Eurypterids, like all arthropods, molted multiple times during their lifespan (Andrews et al. 1974) and shed exoskeletons would have outnumbered living (or dead) individuals at any given time. That being said, molts are far more delicate than carcasses, and also subject to scavenging (albeit to a lesser

29

extent than carcasses), ultimately limiting their potential for preservation. Nevertheless, they appear to form the bulk of the eurypterid fossil record.

The molting features cited earlier, low ECI value, and highly disarticulated nature of the assemblage, suggest that most molts were subjected to tidal activity or storms prior to burial. The lack of tidal structures (e.g., tidal bedding, herringbone cross-stratification, etc.) other than lamination and lack of diagnostic storm indicators (e.g., graded beds, coarse-grained lags, or wave-generated structures such as hummocky cross-stratification) within the eurypterid-bearing horizons at either Winfield Quarry or Atkinson Mills prevents us from ruling out either process, and both may have played a role in specimen disarticulation. That being said, the well-preserved laminae, overall lack of coarse lags/grading/structures, and excellent preservation of nearly complete eurypterids seem to indicate that tidal processes may have been the more overarching influence, even if the tides themselves were amplified mainly by wind, or distant storms. Storms may also explain the rare stenotopic taxa such as nautiloids and bryozoans that occur in the eurypterid-bearing units but were most likely washed in from deeper settings.

Compared to the ECI, the CSAI and CAAI values are relatively high, suggesting that for some specimens environmentally driven disarticulation was minimal. Together, the low ECI value, and high CSAI and CAAI values suggest that some degree of time averaging is responsible for the range of specimen completeness at Winfield Quarry. Time averaging is also supported by the wide range of leperditicopid instar sizes found on the same horizons as the eurypterids: Vannier et al. (2001) considered mixing of small and large leperditicopid instars to be an indication of a lack of significant transport following ecdysis (or death) over an extended period of time.

But how much time do the eurypterid-bearing shale units represent? Although the

30

eurypterid specimens contain no original or vestigial cuticle, as documented at other localities with similar depositional environments (Gupta et al. 2007; Cody et al. 2011), the exuvial remains at Winfield Quarry are, for the most part, preserved in great detail, and, overall, burial must have occurred shortly after ecdysis in order to inhibit breakdown of exoskeletons by chitinoclastic . Studies on modern chitinoclastic bacteria indicate that complete degradation of can take place within a week to several months depending on environmental factors such as oxygen levels, salinity, temperature, and pH (Zobell and Rittenberg 1938; Seki and Taga 1963a,

1963b; Seki 1966; Gooday et al. 1991; Poulicek and Jeuniaux 1991). Marine-based chitinoclastic bacteria are inhibited by the same anoxic and very low or very high salinity conditions (i.e., freshwater–brackish, or briny) that limit soft-tissue destroying and bioturbators.

Although there is no direct evidence for dysoxia/anoxia at Winfield Quarry, the lack of bioturbation, limited faunal diversity, and abundance of chitinous exoskeletons do suggest variable, or non-normal marine salinity and/or dysoxic or anoxic conditions (see above). Under these fluctuating conditions, it seems plausible that the timeframe between the shedding of the first (and presumably most degraded) molts and later, best-preserved specimens was short, perhaps a few weeks to a month.

Trace Fossils.—The traces found on one of the eurypterid fossil horizons at Winfield Quarry may have been formed through a variety of –substrate interactions. Paired tracks may have been created by swimming brushing against the substrate (e.g., Fig. 8A; Fig. 8B, top-right) or pushing off from the substrate (e.g., Fig. 8B, lower-left) with their swimming legs

(appendage VI). The chevron-shaped markings may have been produced by stationary animals balancing on the substrate while being laterally shifted by currents (e.g., Fig. 8C–D). The

31

patchwork of drag traces may have been caused by shed as they drifted in the water column following ecdysis (e.g., Fig. 8A). Taken as a whole, we interpret these traces as chelicerate tracks, most likely from eurypterids, created in the immediate vicinity of the molting site.

The sharp preservation of tracks at this locality may be the result of microbial activity.

Seilacher et al. (1985) and Seilacher (2008) posited that microbial mats on paleosubstrates could lead to the preferential preservation of arthropod trackways (or, more likely, undertracks) that might not otherwise be preserved in the sediment. Fernández and Pazos (2013) suggested a similar method of preservation for xiphosuran trackways in a subaerial beach deposit from the

Cretaceous. Aside from the thrombolites and probable rippled microbial structures under- and overlying the eurypterid-producing beds (Appendix, Chapter II Fig. 1C), secondary evidence for the presence of microbial mats in the Tonoloway Formation is the abundance of gastropods and leperditicopids on some horizons. These organisms may have found a plentiful food source in the bacterial mats (Smosna et al. 1977).

If the tracemakers were eurypterids, this would be the first documented example of eurypterid trace and body fossils co-occurring on the same horizon. There are numerous examples of trackways ascribed to eurypterid producers (e.g., Briggs and Rolfe 1983; Braddy and Milner 1998; Draganits et al. 2001; Whyte 2005; Poschmann and Braddy 2010; Morrissey et al. 2012), but body and associations are rare. Possible arthropod swimming trackways, potentially eurypterid in origin, are known from the upper Silurian Williamsville

Formation A unit (sensu Ciurca 1990) in Ontario, but these occur as hypichnial traces on the undersides of slabs bearing eurypterid fossils (Ciurca 2002). Eurypterid body fossils and putative eurypterid trackways (cf. Palmichnium; Braddy 2001, fig. 3) are also purportedly found in close

32

association within the lower Silurian Whirlpool Formation of Ontario, but these are only known from float and the exact source horizons are unclear (D.M. Rudkin, personal communication

2013).

The co-occurrence of body and trace fossils is significant when interpreting the

Eurypterus sp. habitat. Previous interpretations were primarily based on body fossils, a majority of which were probably molt remains (Tetlie et al. 2008). Molts, being the lightweight counterpart to the shedding organism, are easily transported and may not remain at the site of ecdysis before burial. Assuming that the tracks at Winfield Quarry are those of eurypterids, the close association of body and trace fossils appears to be primary evidence that the eurypterids preserved there were inhabitants of that environment, even if only briefly, rather than taphonomic artifacts following transport. Further, these tracks may also help constrain the potential salinity range within the eurypterid-bearing beds at Winfield Quarry. Subaqueous traces ascribed to Silurian and Devonian eurypterid producers elsewhere are typically found in environments that are interpreted as eu- or hyposaline environments (e.g., Davies et al. 2006;

Marriott et al. 2009; Poschmann and Braddy 2010), rather than hypersaline (cf. Ciurca 2002).

Paleoecology.—As indicated by the taphonomic indices values discussed above, the eurypterids at Winfield Quarry appear to represent molt assemblages on two different horizons, with individual specimens displaying varying degrees of disarticulation. The sheer abundance of eurypterids within these two horizons contrasts sharply with the complete lack of any eurypterid material from adjacent (and well-scouted) strata. This sudden and stratigraphically limited appearance of molts suggests an ephemeral nature to their inhabitation of this environment and the possibility that each horizon consists of specimens from separate molting events. Such an

33

interpretation is consistent with the long-held view that Silurian eurypterids periodically sought out and congregated in shallow, restricted environments such as lagoons or tidal flats, most likely to molt (e.g., Sarle 1903; Ruedemann 1934; Caster and Kjellesvig-Waering 1964; Størmer 1976) and/or to mate or spawn en masse (cf. the “mass-moult-mate” hypothesis, Braddy 2001; Vrazo and Braddy 2011). It seems logical that, like its cohorts in the northern Appalachian basin,

Eurypterus sp. would have used the restricted tidal flat setting of the Tonoloway Formation as a protective environment in which to molt. Similar mass-molting behavior has also been inferred from other Paleozoic arthropod taxa including Canadaspis perfecta and a megacheiran

(Alacomenaeus sp.) from the (Haug et al. 2013), and trilobites (Speyer and Brett 1985;

Karim and Westrop 2002). Mass-mating or spawning behavior among eurypterids, however, is more difficult to prove in the absence of physical evidence such as nests or equivalent traces (but see Le Herisse et al. 2012, for microfossil evidence of putative associated with eurypterids) or behavioral evidence for mating or spawning (i.e., external transfer of a from male to female; cf. Braddy and Dunlop 1997; Kamenz et al. 2011). Further, there is no precedent in the marine chelicerate phylogeny for coupled molting and mating/spawning (Haug et al. 2013), including within the Xiphosura, which are traditionally used as a modern analog for eurypterids. Nonetheless, the presence of juvenile molts at Winfield

Quarry proffers two possible scenarios (or some combination thereof): (1) both juveniles and adults migrated into these settings to molt en masse; (2) this shallow-water environment may have served as a nursery proximal to a breeding site (cf. Braddy 2001; Haug et al. 2013).

Paleoenvironmental and Sea-Level Controls on Fossilization

The positioning of the eurypterid-bearing beds at Winfield Quarry and Atkinson Mills

34

just above a thrombolitic unit (indicative of early transgressive conditions) and the intertidal zone of a mudflat suggests that the fossil horizons occur slightly above the flooding surface of a regional-scale transgression that precedes the Keyser Formation. (This transgression may be correlative to the late Ludlow–early Přídolí transgression documented by Johnson et al. [1998], but higher-precision age data are needed to link the stratigraphy to these well-documented sea- level fluctuations.) We suggest that the occurrence of eurypterids within this succession is specifically due to changes in the local environment resulting from this transgression, rather than merely by chance or by storm deposition. Although we cannot entirely rule out that the beds on which the eurypterids occur simply represent one or two storm-driven deposits containing molts washed in from a deeper, subtidal setting (as discussed above), the accompanying trace fossils appear to discount this possibility. Additionally, we believe that the regional paucity of eurypterids elsewhere in the Tonoloway Formation is an indication of their preference for environmental conditions created as a result of sea-level rise. The regular cycling between sub- and supratidal successions within the Tonoloway Formation, and the frequently restricted, occasionally hypersaline conditions created therein, would be highly conducive to burial and preservation of soft tissues, but would also be hostile to all but the most tolerant organisms including, presumably, eurypterids (Kluessendorf and Mikulic 1991; Kluessendorf 1994). The appearance of eurypterids at Winfield Quarry and Atkinson Mills in only the initial portion of a deepening interval suggests that Eurypterus sp. was not a regular inhabitant of most nearshore settings within the Tonoloway Formation, and instead may have been tracking some ideal salinity or environmental condition created following flooding of the tidal flat (cf. Clarke and

Ruedemann 1912; Leutze 1961).

In this scenario, the burial of molts in the Turbotville Member of the Tonoloway

35

Formation at Winfield Quarry and Atkinson Mills would be the result of both environmental influences, i.e., rising sea level within a tidal mudflat setting, and behavioral traits that led eurypterids to gather in these localities en masse. The end result is a Konservat-Lagerstätte preserved within a narrow taphonomic window, but one that is not reliant on unique preservational parameters inasmuch as it is created by a normal transgressive event within a geographically broad marginal setting frequented by eurypterids. A similar pattern of sequence stratigraphic control on eurypterid occurrences has been noted in the northern Appalachian basin, e.g., in the Bertie Group of New York (e.g., Ciurca 1973, 1990), and elsewhere in Laurentia, e.g.,

Somerset Island, Canada (Dixon and Jones 1978; Jones and Kjellesvig-Waering 1985), and

Baltica, e.g., Saaremaa Island, Estonia (Viira and Einasto 2003; Meidla et al. 2014) and this pattern warrants further study.

In summary, we conclude that the presence of eurypterids on correlative horizons at two geographically distant localities—Winfield Quarry and Atkinson Mills—is an early indication of the regional scale at which Eurypterus may have occurred within the central Appalachian basin, and offers further support for Kluessendorf's (1994) argument for the prospecting of additional

Lagerstätten within this region. The apparent absence of eurypterids at other exposures geographically closer to Winfield Quarry is probably due to a lack of well-exposed dip slopes at these localities, rather than a preservational reality. Additional fieldwork in this region should yield more occurrences, and with them, further evidence for eurypterid inhabitance of the nearshore environment of the central Appalachian basin during the late Silurian.

CONCLUSIONS

1. A Eurypterus Lagerstätte from the upper Silurian Tonoloway Formation of

36

Pennsylvania has provided the first evidence of mass assemblages of eurypterids in the central

Appalachian basin.

2. Eurypterus sp. occurs within the lower intertidal to shallow subtidal zone of a mudflat deposited along a gently dipping carbonate ramp. Associated fauna are rare and diversity is low, reflective of a restricted marginal-marine environment with variable salinity.

3. Most eurypterid specimens are disarticulated to some extent, but some are almost fully articulated. Taphonomic indices suggest a parautochthonous molt assemblage with limited transport, similar to molt assemblages in the northern Appalachian basin.

4. Trace fossils offer probable direct evidence that eurypterids may have occasionally inhabited this environment. Deposition here is probably not the result of transport from a life habitat elsewhere.

5. The preservation of a monospecific assemblage of molts from both juvenile and adult instars from one species suggests that Eurypterus sp. may have congregated within a quiet marginal setting for the purposes of molting, and, perhaps, mating en masse (cf. Braddy 2001).

Juvenile instars may have also used this setting as a protective setting during early development.

6. The occurrence of eurypterids at two distant localities on correlative horizons within the transgressive stage of a stratigraphic sequence suggests that their occurrence is due to environmental preference, rather than a taphonomic artifact or bias.

7. The discovery of a Lagerstätte away from the northern region of the Appalachian basin suggests that the paucity of eurypterid specimens from the late Silurian of the central basin may be the result of undercollecting rather than a taphonomic or ecological reality.

37

ACKNOWLEDGMENTS

We would like to thank Samuel J. Ciurca, Jr. for general discussion, location references, and specimen identification. James C. Lamsdell and O. Erik Tetlie are thanked for specimen identification. James W. Hagadorn and James R. Thomka are thanked for thoughtful trace fossil discussion. Susan Butts and Jessica Utrup (Yale Peabody Museum) provided collections assistance. Edward Cotter provided detailed and insightful comments which improved an earlier version of this manuscript. We would like to thank Peter Van Roy, an anonymous reviewer, and

John-Paul Zonneveld for their valuable remarks and constructive comments. We greatly appreciate the contributions of many Bucknell University and University of Cincinnati students who helped us collect eurypterid specimens at Winfield Quarry, including Kait Fleming who discovered the first specimen, and we thank personnel at Eastern Industries Inc., including Albert

Mabus, for facilitating routine access to the field site. This study was supported by a Caster Fund

Research Grant (University of Cincinnati) and the Schuchert and Dunbar Grant-in-Aid Program

(Yale Peabody Museum).

38

REFERENCES

Alling, H.A., and Briggs, L.I., 1961, Stratigraphy of upper Silurian Cayugan evaporites:

American Association of Petroleum Geologists (AAPG) Bulletin, v. 45, p. 515–547, doi:

10.1306/bc743673-16be-11d7-8645000102c1865d.

Anderson, L.I., Clarkson, E.N.K., Stewart, S.E., and Mitchell, D., 2007, An upper Llandovery

Konservat–Lagerstätte in a depositional context: the Pentland Hills Eurypterid Bed,

Midlothian: Scottish Journal of Geology, v. 43, p. 41–50, doi: 10.1144/sjg43010041.

Andrews, H.E., Brower, J.C., Gould, S.J., and Reyment, R.A., 1974, Growth and variation in

Eurypterus remipes DeKay: Bulletin of the Geological Institution of the University of

Uppsala, New Series, v. 4, p. 81–114.

Belak, R., 1980, The Cobleskill and Akron Members of the Rondout Formation; late Silurian

carbonate shelf sedimentation in the Appalachian basin, New York State: Journal of

Sedimentary Research, v. 50, p. 1187–1204, doi: 10.1306/212f7ba8-2b24-11d7-

8648000102c1865d.

Bell, S.C., and Smosna, R., 1999, Regional facies analysis and carbonate ramp development in

the Tonoloway Limestone (U. Silurian; central Appalachians): Southeastern Geology, v.

38, p. 259–278.

Braddy, S.J., 2001, Eurypterid palaeoecology: palaeobiological, ichnological and comparative

evidence for a “mass-moult-mate” hypothesis: Palaeogeography, Palaeoclimatology,

Palaeoecology, v. 172, p. 115–132.

39

Braddy, S.J., and Dunlop, J.A., 1997, The functional morphology of mating in the Silurian

eurypterid, Baltoeurypterus tetragonophthalmus (Fischer, 1839): Zoological Journal of

the Linnean Society, v. 120, p. 435–461.

Braddy, S.J., and Milner, A.R.C., 1998, A large arthropod trackway from the Gaspe

Group (Middle Devonian) of eastern Canada: Canadian Journal of Earth Sciences, v. 35,

p. 1116–1122.

Braddy, S.J., Aldridge, R.J., and Theron, J.N., 1995, A new eurypterid from the Late Ordovician

Table Mountain Group, : Palaeontology, v. 38, p. 563–581.

Brett, C.E., 1989, Silurian of western and central New York State, in Woodrow, D.L., Brett, C.E.,

and Selleck, B., eds., Sedimentary Sequences in a Foreland Basin: The New York

System: Fieldtrip Guidebook T156, 28th International Geological Congress, American

Geophysical Union, p. 7–15.

Briggs, D.E.G., and Rolfe, W.D.I., 1983, A giant arthropod trackway from the Lower

Mississippian of Pennsylvania: Journal of Paleontology, v. 57, p. 377–390.

Brower, J.C., and Veinus, J., 1978, Multivariate analysis of allometry using point coordinates:

Journal of Paleontology, v. 52, p. 1037–1053, doi: 10.2307/1303849.

Carter, K.M., 2007, Subsurface rock correlation diagram, oil and gas producing regions of

Pennsylvania, Pennsylvania Geological Survey, 4th series,

http://www.dcnr.state.pa.us/topogeo/publications/pgspub/openfile/drc/index.htm.

Checked August, 2014.

40

Caster, K.E., 1938, A restudy of the tracks of Paramphibius: Journal of Paleontology, v. 12, p. 3–

60, doi: 10.2307/1298395.

Caster, K.E., and Kjellesvig-Waering, E.N., 1964, Upper Ordovician eurypterids of Ohio:

Palaeontographica Americana, v. 4, p. 297–358.

Ciurca, S.J., Jr., 1973, Eurypterid horizons and the stratigraphy of upper Silurian and Lower

Devonian rocks of western New York State, in New York State Geological Association,

45th Annual Meeting, Monroe Community College and SUNY College at Brockport,

New York, p. D1–D14.

Ciurca, S.J., Jr., 1990, Eurypterid biofacies of the Silurian–Devonian evaporite sequence:

Niagara Penninsula, Ontario, Canada and New York State, in Lash, G.G., ed., New York

State Geological Association, 62nd Annual Meeting, Fredonia, New York, p. D1–D23.

Ciurca, S.J., Jr., 2002, A new trace fossil horizon within the late Silurian, eurypterid-bearing,

Bertie Group in Ontario, Canada: M.A.P.S. (Mid-America Paleontology Society) Digest

(Expo XXIV edition, 2002: Ichnology), v. 25, p. 52–56.

Ciurca, S.J., Jr., 2010, Eurypterids Illustrated: The Search for Prehistoric Sea Scorpions:

Rochester, New York, Paleo Research, 30 p.

Ciurca, S.J., Jr., 2011, Silurian and Devonian eurypterid horizons in upstate New York, in

Fieldtrip Guidebook, New York State Geological Association, 83rd Annual Meeting, p.

139–151.

Clarke, J.M., and Ruedemann, R., 1912, The Eurypterida of New York:

41

Memoir, v. 14, p. 1–439.

Cody, G.D., Gupta, N.S., Briggs, D.E.G., Kilcoyne, A.L.D., Summons, R.E., Kenig, F., Plotnick,

R.E., and Scott, A.C., 2011, Molecular signature of chitin- complex in Paleozoic

arthropods: Geology, v. 39, p. 255–258, doi: 10.1130/g31648.

Copeland, M.J., and Bolton, T.E., 1985, Fossils of Ontario, Part 3: The Eurypterids and

Phyllocarids: Toronto, Canada, , 48 p.

Cotter, E.C., and Inners, J.D., 1986, Stop 1.5; Allenport, in Sevon, W.D., ed., Selected Geology

of Bedford and Huntington Counties: Guidebook, 51st Annual Field Conference of

Pennsylvania Geologists, Juniata University, Huntington, Pennsylvania, p. 27–39.

Davies, N.S., Sansom, I.J., and Turner, P., 2006, Trace fossils and paleoenvironments of a late

Silurian marginal-marine/alluvial system: the Ringerike Group (Lower Old Red

Sandstone), Oslo Region, Norway: PALAIOS, v. 21, p. 46–62, doi:

10.2110/palo.2003.p03-08.

Dennison, J.M., and Head, J.W., 1975, Sealevel variations interpreted from the Appalachian

basin Silurian and Devonian: American Journal of Science, v. 275, p. 1089–1120, doi:

10.2475/ajs.275.10.1089.

Dixon, O.A., and Jones, B., 1978, Upper Silurian Leopold Formation in the Somerset-Prince

Leopold Islands type area, Arctic Canada: Bulletin of Canadian Petroleum Geology, v.

26, p. 411–423.

Dorobek, S.L., and Read, J.F., 1986, Sedimentology and basin evolution of the Siluro-Devonian

42

Helderberg Group, Central Appalachians: Journal of Sedimentary Research, v. 56, p.

601–613.

Draganits, E., Braddy, S.J., and Briggs, D.E.G., 2001, A Gondwanan coastal arthropod

ichnofauna from the Muth Formation (Lower Devonian, northern India):

Paleoenvironment and tracemaker behavior: PALAIOS, v. 16, p. 126–147.

Dunlop, J.A., and Webster, M., 1999, Fossil evidence, terrestrialization and phylogeny:

Journal of , v. 27, p. 86–93.

Ehlinger, G.S., and Tankersley, R.A., 2004, Survival and development of

( polyphemus) and larvae in hypersaline conditions: The Biological

Bulletin, v. 206, p. 87–94.

Elick, J.M., Brown, K.M., and Siegel, M., 2009, Paleoecology and cyclicity of the Tonoloway

Formation and Keyser Formations: a guide to understanding limestone composition in

Mandata, PA: Geological Society of America Abstracts with Programs, v. 41, p. 118.

Ettensohn, F.R., and Brett, C.E., 2002, Stratigraphic evidence from the Appalachian Basin for

continuation of the Taconian orogeny into early Silurian time: Physics and Chemistry of

the Earth, Parts A/B/C, v. 27, p. 279–288, doi: 10.1016/S1474-7065(01)00010-9.

Fernández, D.E., and Pazos, P.J., 2013, Xiphosurid trackways in a Lower tidal flat in

Patagonia: palaeoecological implications and the involvement of microbial mats in trace-

fossil preservation: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 375, p. 16–

29, doi: 10.1016/j.palaeo.2013.02.008.

43

Gooday, G.W., Prosser, J.I., Hillman, K., and Cross, M.G., 1991, Mineralization of chitin in an

estuarine sediment: the importance of the chitosan pathway: Biochemical Systematics

and Ecology, v. 19, p. 395–400, doi: 10.1016/0305-1978(91)90056-6.

Gupta, N.S., Tetlie, O.E., Briggs, D.E.G., and Pancost, R.D., 2007, The fossilization of

eurypterids: a result of molecular transformation: PALAIOS, v. 22, p. 439–447, doi:

10.2110/palo.2006.p06-057r.

Haug, J., Caron, J.-B., and Haug, C., 2013, Demecology in the Cambrian: synchronized molting

in arthropods from the : BMC (BioMedCentral) Biology, v. 11, p. 1–10,

doi: 10.1186/1741-7007-11-64.

Hess, A.V., 2008, Sedimentological and geochemical analysis of the Keyser and Old Port

Formations, Central Pennsylvania: improved constraints on late Silurian–Early Devonian

paleoenvironmental conditions: Unpublished B.S. thesis, Bucknell University,

Lewisburg, Pennsylvania, 79 p.

Heubusch, C.A., 1962, Preservation of the intestine in three specimens of Eurypterus: Journal of

Paleontology, v. 36, p. 222–224, doi: 10.2307/1301103.

Heyman, L., 1977, Tully (Middle Devonian) to Queenston (Upper Ordovician) correlations in the

subsurface of western Pennsylvania: Pennsylvania Geological Survey, 4th ser., Mineral

Resource Report 73, 16 p.

Hoskins, D.M., 1976, Geology and mineral resources of the Millersburg 15-minute quadrangle,

Dauphin, Juniata, Northumberland, Perry, and Snyder Counties, Pennsylvania:

44

Pennsylvania Geological Survey, Atlas 146, scale 1:24,000, Harrisburg, 38 p.

Inners, J.D., 1981, Geology and mineral resources of the Bloomsburg and Mifflinville

quadrangles and part of the Catawissa quadrangle, Columbia County, Pennsylvania:

Pennsylvania Geological Survey, Atlas 164cd, Harrisburg, 152 p.

Inners, J.D., 1997, Geology and mineral resources of the Allenwood and Milton quadrangles,

Union and Northumberland Counties, Pennsylvania: Pennsylvania Geological Survey, 4th

ser., Atlas 144cd, Harrisburg, 135 p.

Johnson, M.E., Rong, J.-Y., and Kershaw, S., 1998, Calibrating Silurian eustasy by erosion and

burial of coastal paleotopography, in Landing, E., and Johnson, M.E., eds., Silurian

Cycles: Linkages of Dynamic Stratigraphy with Atmospheric, Oceanic, and Tectonic

Changes: New York State Museum Bulletin No. 491, p. 3–13.

Jones, B., and Dixon, O.A., 1974, The Leopold Formation: an upper Silurian intertidal/supratidal

carbonate succession on northeastern Somerset Island, Arctic Canada: Canadian Journal

of Earth Sciences, v. 12, p. 395–411, doi: 10.1139/e75-036.

Jones, B., and Kjellesvig-Waering, E.N., 1985, Upper Silurian eurypterids from the Leopold

Formation, Somerset Island, Arctic Canada: Journal of Paleontology, v. 59, p. 411–417,

doi: 10.2307/1305035.

Kamenz, C., Staude, A., and Dunlop, J.A., 2011, carriers in Silurian sea scorpions:

Naturwissenschaften, v. 98, p. 889–896, doi: 10.1007/s00114-011-0841-9.

Karim, T., and Westrop, S.R., 2002, Taphonomy and paleoecology of Ordovician

45

clusters, Bromide Formation, south-central : PALAIOS, v. 17, p. 394–402, doi:

10.2307/3515763.

Kjellesvig-Waering, E.N., 1950, A new Silurian from West Virginia: Journal of

Paleontology, v. 24, p. 226–228.

Kjellesvig-Waering, E.N., 1958, The genera, species and subspecies of the family Eurypteridae,

Burmeister, 1845: Journal of Paleontology, v. 32, p. 1107–1148.

Kjellesvig-Waering, E.N., 1961, The Silurian Eurypterida of the Welsh Borderland: Journal of

Paleontology, v. 35, p. 789–835, doi: 10.2307/1301214.

Kjellesvig-Waering, E.N., and Heubusch, C.A., 1962, Some Eurypterida from the Ordovician

and Silurian of New York: Journal of Paleontology, v. 36, p. 211–221.

Kjellesvig-Waering, E.N., and Leutze, W.P., 1966, Eurypterids from the Silurian of West

Virginia: Journal of Paleontology, v. 40, p. 1109–1122.

Kluessendorf, J., 1994, Predictability of Silurian Fossil-Konservat-Lagerstätten in North-

America: Lethaia, v. 27, p. 337–344.

Kluessendorf, J., and Mikulic, D., 1991, The role of anoxia in the formation of Silurian

Konservat-Lagerstätten: Geological Society of America Abstracts with Programs, Annual

Meeting, Northeastern and Southeastern sections, Baltimore, v. 23, p. 54.

Lamsdell, J.C., 2011, The eurypterid Stoermeropterus conicus from the lower Silurian of the

Pentland Hills, Scotland: Monograph of the Palaeontographical Society, v. 165, p. 1–84.

46

Lamsdell, J.C., 2013, Revised systematics of Palaeozoic “horseshoe crabs” and the myth of

monophyletic Xiphosura: Linnean Society, Zoological Journal, v. 167, p. 1–27, doi:

10.1111/j.1096-3642.2012.00874.x.

Lamsdell, J.C., and Braddy, S.J., 2010, Cope's Rule and Romer's theory: patterns of diversity and

gigantism in eurypterids and Palaeozoic : Biology Letters, v. 6, p. 265–269,

doi: 10.1098/rsbl.2009.0700.

Lamsdell, J.C., Hoşgör, İ., and Selden, P.A., 2013, A new Ordovician eurypterid (Arthropoda:

Chelicerata) from southeast Turkey: Evidence for a cryptic Ordovician record of

Eurypterida: Gondwana Research, v. 23, p. 354–366, doi: 10.1016/j.gr.2012.04.006.

Laughrey, C.D., 1999, Silurian and Transition to Devonian, in Shultz, C.H., ed., The Geology of

Pennsylvania: Pennsylvania Geological Survery, Harrisburg, and Pittsburgh Geological

Society, Pittsburgh, p. 90–107.

Le Herisse, A., Masure, E., Javaux, E.J., and Marshall, C.P., 2012, The end of a myth: Arpylorus

antiquus Paleozoic dinoflagellate cyst: PALAIOS, v. 27, p. 414–423, doi:

10.2110/palo.2011.p11-110r.

Leutze, W.P., 1960, Silurian eurypterids from West Virginia: Journal of Paleontology, v. 34, p.

1023–1026.

Leutze, W.P., 1961, Arthropods from the Syracuse Formation, Silurian of New York: Journal of

Paleontology, p. 49–64.

Ludlum, J.C., 1959, Rock salt, rhythmic bedding, and salt-crystal impressions in the upper

47

Silurian of West Virginia: Southeastern Geology, v. 1, p. 22–31.

Makurath, J.H., 1977, Marine faunal assemblages in the Silurian–Devonian Keyser Limestone of

the central Appalachians: Lethaia, v. 10, p. 235–256, doi: 10.1111/j.1502-

3931.1977.tb00618.x.

Manning, P.L., 1993, Palaeoecology of the eurypterids of the upper Silurian of the Welsh

Borderland: Unpublished M.S. thesis, University of Manchester, Manchester, UK, 141 p.

Marriott, S.B., Morrissey, L.B., and Hillier, R.D., 2009, Trace fossil assemblages in upper

Silurian tuff beds: evidence of biodiversity in the Old Red Sandstone of southwest Wales,

UK: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 274, p. 160–172, doi:

10.1016/j.palaeo.2009.01.001.

Meidla, T., Tinn, O., and Männik, P., 2014, Stop B8: Soeginina cliff, in Bauert, H., Hints, O.,

Meidla, T., and Männik, P., eds., Abstracts and Field Guide, 4th Annual Meeting of IGCP

591, Estonia, 10–19 June 2014: University of Tartu, Tartu, Estonia, p. 194–196.

Morrissey, L.B., Hillier, R.D., and Marriott, S.B., 2012, Late Silurian and Early Devonian

terrestrialisation: ichnological insights from the Lower Old Red Sandstone of the Anglo-

Welsh basin, U.K: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 337–338, p.

194–215, doi: 10.1016/j.palaeo.2012.04.018.

Plotnick, R.E., 1999, Habitat of Llandoverian–Lochkovian eurypterids, in Boucot, A.J., and

Lawson, J.D., eds., Paleocommunities, A Case Study from the Silurian and Lower

Devonian: Cambridge, UK, Cambridge University Press, p. 106–131.

48

Poschmann, M., and Braddy, S., 2010, Eurypterid trackways from Early Devonian tidal facies of

Alken an der Mosel (Rheinisches Schiefergebirge, ): Palaeobiodiversity and

Palaeoenvironments, v. 90, p. 111–124, doi: 10.1007/s12549-010-0024-2.

Poulicek, M., and Jeuniaux, C., 1991, Chitin biodegradation in marine environments: an

experimental approach: Biochemical Systematics and Ecology, v. 19, p. 385–394, doi:

10.1016/0305-1978(91)90055-5.

Rasband, W., 2011, ImageJ, Ver. 1.44: National Institutes of Health, Bethesda, Maryland,

http://imagej.nih.gov/ij/. Checked August 2014.

Reger, D.B., 1924, Mineral and Grant Counties: West Virginia Geological Survey County

Reports, 866 p.

Rickard, L.V., 1969, Stratigraphy of the upper Silurian Salina Group: New York, Pennsylvania,

Ohio, Ontario: University of the State of New York, State Education Dept., Albany, 57 p.

Ruedemann, R., 1934, Eurypterids in graptolite shales: American Journal of Science, Series 5

Vol. 27, p. 374–385, doi: 10.2475/ajs.s5-27.161.374.

Sarle, C.J., 1903, A new eurypterid fauna from the base of the Salina of western New York: New

York State Museum Bulletin, v. 69, p. 1080–1108.

Schuchert, C., 1903, On the lower Devonic and Ontaric Formations of Maryland: Proceedings of

the National Museum, v. 26, p. 413–424.

Seilacher, A., 2008, Biomats, biofilms, and bioglue as preservational agents for arthropod

49

trackways: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 270, p. 252–257, doi:

10.1016/j.palaeo.2008.07.011.

Seilacher, A., Reif, W.E., Westphal, F., Riding, R., Clarkson, E.N.K., and Whittington, H.B.,

1985, Sedimentological, ecological and temporal patterns of fossil Lagerstätten [and

discussion]: Philosophical Transactions of the Royal Society of London. Series B,

Biological Sciences, v. 311, p. 5–24, doi: 10.2307/2396966.

Seki, H., 1966, Microbiological studies on the decomposition of chitin in marine environment.

X. Decomposition of chitin in marine sediments: Journal of the Oceanographical Society

of Japan, v. 21, p. 265–269.

Seki, H., and Taga, N., 1963a, Microbiological studies on the decomposition of chitin in marine

environment. II. Influence of some environmental factors on the growth and activity of

marine chitinoclastic bacteria: Journal of the Oceanographical Society of Japan, v. 19, p.

109–111.

Seki, H., and Taga, N., 1963b, Microbiological studies on the decomposition of chitin in marine

environment. III. Aerobic decomposition of chitin by the isolated chitinoclastic bacteria:

Journal of the Oceanographical Society of Japan, v. 19, p. 143–151.

Smosna, R., and Warshauer, S.M., 1981, Rank exposure index on a Silurian carbonate tidal flat:

Sedimentology, v. 28, p. 723–731.

Smosna, R., Patchen, D., Warshauer, S., and Perry, J., W., 1977, Relationships between

depositional environments, Tonoloway Limestone, and distribution of evaporites in the

50

Salina Formation, West Virginia, in Fisher, J.H., Studies in Geology 5: Reefs and

Evaporites: Concepts and Depositional Models: Tulsa, Oklahoma, American Association

of Petroleum Geologists, p. 125–143.

Smosna, R., Bruner, K.R., and Burns, A., 1999, Numerical analysis of sandstone composition,

provenance, and paleogeography: Journal of Sedimentary Research, v. 69, p. 1063–1070.

Speyer, S.E., and Brett, C.E., 1985, Clustered trilobite assemblages in the Middle Devonian

Hamilton Group: Lethaia, v. 18, p. 85–103, doi: 10.1111/j.1502-3931.1985.tb00688.x.

Størmer, L., 1955, Merostomata, in Moore, R.C., ed., Treatise on Paleontology. Part

P. Arthropoda 2: Geological Society of America and University of Press,

Lawrence, Kansas, p. 4–41.

Størmer, L., 1976, Arthropods from the Lower Devonian (lower ) of Alken an der Mosel,

Germany. Part 5: and additional forms, with general remarks on fauna and

problems regarding invasion of land by arthropods: Senckenbergiana Lethaea, v. 57, p.

87–183.

Swartz, C.K., 1923, Order Eurypterida, in Swartz, C.K., Prouty, W.F., Ulrich, E.O., and Bassler,

R.S., eds., Silurian Volume: Baltimore, Maryland, Maryland Geological Survey, p. 716–

778.

Tetlie, O.E., 2006, Two new Silurian species of Eurypterus (Chelicerata: Eurypterida) from

Norway and Canada and the phylogeny of the genus: Journal of Systematic

Palaeontology, v. 4, p. 397–412, doi: 10.1017/s1477201906001921.

51

Tetlie, O.E., 2007, Distribution and dispersal history of Eurypterida (Chelicerata):

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 252, p. 557–574, doi:

10.1016/j.palaeo.2007.05.011.

Tetlie, O.E., and Ciurca, S.J., Jr., 2005, Analysis of the completeness of eurypterid remains: Fall

Meeting of the Rochester Academy of Science, Finger Lake Community College,

Canandaigua, New York, p. 45.

Tetlie, O.E., Tollerton, V., and Ciurca, S.J., Jr., 2007, Eurypterus remipes and E. lacustris

(Chelicerata: Eurypterida) from the Silurian of North America: Bulletin of the Peabody

Museum of Natural History, v. 48, p. 139–152, doi: 10.3374/0079-

032x(2007)48[139:eraelc]2.0.co;2.

Tetlie, O.E., Brandt, D.S., and Briggs, D.E.G., 2008, Ecdysis in sea scorpions (Chelicerata :

Eurypterida): Palaeogeography, Palaeoclimatology. Palaeoecology, v. 265, p. 182–194,

doi: 10.1016/j.palaeo.2008.05.008.

Tilton, J.L., Prouty, W.F., Tucker, R.C., and Price, P.H., 1927, Hampshire and Hardy counties:

West Virginia Geological Survey, Morgantown, 624 p.

Tollerton, V.P., Jr., 1989, Morphology, , and classification of the order Eurypterida

Burmeister, 1843: Journal of Paleontology, v. 63, p. 642–657, doi: 10.2307/1305624.

Tourek, T.J., 1970, The depositional environments and sediment accumulation models for the

upper Silurian Wills Creek shale and Tonoloway limestone, central Appalachians:

Unpublished Ph.D. thesis, Johns Hopkins University, Baltimore, Maryland, 564 p.

52

Vannier, J., Wang, S.Q., and Coen, M., 2001, Leperditicopid arthropods (Ordovician–Late

Devonian): functional morphology and ecological range: Journal of Paleontology, v. 75,

p. 75–95.

Viira, V., and Einasto, R., 2003, Wenlock-Ludlow boundary beds and of Saaremaa

Island, Estonia: Proceedings of the Estonian Academy of Sciences, Geology, v. 52, p.

213–238.

Vrazo, M.B., and Braddy, S.J., 2011, Testing the “mass-moult-mate” hypothesis of eurypterid

palaeoecology: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 311, p. 63–73,

doi: 10.1016/j.palaeo.2011.07.031.

Vrazo, M.B., Hunda, B.R., and Brett, C.E., 2013, Semi-landmark analysis of eurypterids: a new

tool for assessing ecophenotypy: Geological Society of America Abstracts with

Programs, v. 45, p. 458.

Warshauer, S.M., and Smosna, R., 1977, Paleoecologic controls of the ostracode communities in

the Tonoloway Limestone (Silurian; Pridoli) of the central Appalachians, in Loffler, H.,

and Danielopol, D., eds., Aspects of Ecology and Zoogeography of Recent and Fossil

Ostracoda: W. Junk, The Hague, p. 475–485.

Whyte, M.A., 2005, Palaeoecology: a gigantic fossil arthropod trackway: Nature, v. 438, p. 576–

576.

Woodward, H.P., 1941, Silurian system of West Virginia: Parkersburg, West Virginia, Scholl

Printing Company, 326 p.

53

Young, G.A., Rudkin, D.M., Dobrzanski, E.P., Robson, S.P., and Nowlan, G.S., 2007,

Exceptionally preserved Late Ordovician biotas from Manitoba, Canada: Geology, v. 35,

p. 883-886, doi: 10.1130/g23947a.1.

Zobell, C.E., and Rittenberg, S.C., 1938, The occurrence and characteristics of chitinoclastic

bacteria in the sea: Journal of Bacteriology, v. 35, p. 275–287.

54

FIGURES

55

FIGURE 1. Regional map of the North American Appalachian basin. Shaded area represents known exposures of Silurian-age units; known Eurypterus localities, including study locality

(Winfield, PA), are starred. In New York and Ontario, where Eurypterus is known from numerous localities, the Ft. Erie and Herkimer markers bound its approximate east–west range.

56

FIGURE 2. Map showing bedrock geology of the study area. Rectangle at east end of West

Quarry marks the location of most eurypterid fossil collection during this study and the location of field photos shown in Figures 3–4, and measured stratigraphic section in Figure 5A.

Abbreviations of Silurian–Devonian formations listed from oldest to youngest: Silurian—St =

Tuscarora Formation, Sc = , Sbm = Mifflintown and Bloomsburg Formations, Swc

= Wills Creek Formation; Silurian–Devonian—DSkt = Tonoloway and Keyser Formations;

Devonian—Doo = Onondaga and Old Port Formations, Dh = , Dtr = Trimmers

Rock Formation. Adapted from Hoskins (1976).

57

FIGURE 3. Field photographs showing key stratigraphic and sedimentological features of the

Winfield Quarry eurypterid fossil locality. Scales are as follows: A, F–no scale; B–person; C– hammer; D–camera lens cap; E–10-cm-long photo scale. A) Western part of Winfield Quarry showing uppermost Tonoloway Formation and overlying Keyser and Old Port Formations. Note dip slopes along right side of road where stratigraphic section (Fig. 5A) was measured and photos B–F and Fig. 4A–F were taken. E = area where nearly all eurypterid fossils were

58

recovered. View toward the west. B) Uppermost Tonoloway Formation stratigraphy showing four key lithofacies associations from ~20 to 180 cm above base of measured section: D = micrite with desiccation cracks, T = micrite with thrombolites, L = laminated calcareous shale with eurypterid fossils, and P = interbedded limestone packstone, and subordinate grainstone/rudstone. View is toward the east. C) Desiccation cracks in micrite ~20 cm above base of measured section. D–E) Thrombolites ~40 cm above base of measured section. Note shaley laminae draping upon thrombolite in Part E. F) Thinly laminated calcareous shale 60–75 cm above base of measured section (continued in Fig. 4A).

59

FIGURE 4. Field photographs showing key stratigraphic and sedimentological features of the

Winfield Quarry eurypterid fossil locality. Note 10-cm-long photo scale in all photos except Part

C (person) and Part D (clipboard). A–B) Thinly laminated calcareous shale 60–75 cm above base of measured section including close-up of laminae in Part A and syneresis cracks in Part B. C)

Transition from calcareous shale (=L) to interbedded micrite, packstone, and minor grainstone

(=P). Interval shown is ~70–720 cm above base of measured section. D) Low-amplitude,

60

straight-crested ripples in wackestone/packstone ~575 cm above base of measured section. E)

Poorly sorted rudstone with micritic intraclasts ~750 above base of measured section. F)

Fragmented cladopora? and leperditicopid fossils ~770 cm above base of measured section.

61

FIGURE 5. Lithological sections of study localities. A) Winfield Quarry, Pennsylvania. B)

Atkinson Mills, Pennsylvania.

62

FIGURE 6. Eurypterus sp., Tonoloway Formation, Winfield Quarry, Pennsylvania. Scale bars =

1 cm. A) Juvenile, preserved obliquely (YPM 560631). B) Juvenile (YPM 560634). C) Adult,

63

appendages III–V visible on left (YPM 560644). D) Isolated carapaces; the first tergite is attached to the two specimens on the left (YPM 560638, 560640, and 560641). E) Specimen with both swimming legs (appendage XI) attached (YPM 560642).

64

FIGURE 7. Eurypterids from the Tonoloway Formation, Winfield Quarry, Pennsylvania. Scale bars = 1 cm; ruler scale in cm. A) Eurypterus sp., nearly fully articulated (YPM 560633); B)

Eurypterus sp., ventral-side up with appendages IV–VI visible, surrounded by disarticulated segment hash (YPM 560646). C) ?Dolichopterus, partial carapace (YPM 560637); D)

65

Eurypterus sp., ventral-side up (YPM 560636); and genital appendage are visible. E)

Isolated pterygotid finger (YPM 560635).

66

FIGURE 8. Trace fossils from the Tonoloway Formation, Winfield Quarry, Pennsylvania. Scale bars = 1 cm; ruler scale in cm. A) Trace ensemble (YPM 560645). B) Paired paddle-like traces

(lower center) adjacent to deep paired drag marks (upper right) (YPM 560639). C) Trace ensemble (YPM 560643). D) Close-up of central portion of C; chevron-shaped (lower left) and trifurcated appendage (upper right) markings as well as a medial (telson?) drag mark (center right) are visible.

67

FIGURE 9. Eurypterus sp., Tonoloway Formation, Atkinson Mills, Pennsylvania. Scale bars = 1 cm. A) Isolated carapace (YPM 215893). B) Isolated carapace (YPM 215883). C) Partial sternite

(YPM 560630). D) Palette of swimming leg (appendage XI) (YPM 560632).

68

FIGURE 10. Size-frequency distribution of Eurypterus sp. carapaces from the Tonoloway

Formation, Winfield Quarry, Pennsylvania (n = 50).

69

Chapter III

Vrazo, M.B., Brett, C.E., Ciurca, S.J., Jr., 2016. Buried or brined? Eurypterids and evaporites in

the Silurian Appalachian basin. Palaeogeography Palaeoclimatology Palaeoecology 444.

Matthew B. Vrazo1, Carlton E. Brett1, and Samuel J. Ciurca, Jr2

1Department of Geology, 500 Geology/Physics Building, University of Cincinnati, Cincinnati,

Ohio 45221-0013 USA

22457 Culver Road, Rochester, NY, 14609, USA

Keywords: Salina/Bertie groups, Eurypterus, salt hopper, diagenesis, arthropod paleoecology hypersalinity

70

ABSTRACT

Eurypterid-bearing deposits from the late Silurian Appalachian basin are typically viewed as having been deposited under hypersaline conditions. These interpretations are based on the close association of abundant eurypterid remains with evaporite deposits and structures such as salt hoppers in the Salina and Bertie groups. To determine if this association reflects life habitat, or is the result of taphonomic or diagenetic processes, the co-occurrence of eurypterids and salt hoppers in the upper Silurian Appalachian basin was examined at several stratigraphic scales. A survey of eurypterid remains from the prolific Ellicott Creek Breccia Member of the Fiddlers

Green Formation (Bertie Group) found that 2% of the 479 specimens surveyed are crosscut by salt hoppers or incipient halite structures. In a regional survey, displacive salt hoppers occurred in the same bed as eurypterid remains in 37% (19:51) of all eurypterid-bearing units. In these units, salt hoppers were typically the only structures found intimately associated with eurypterids, sometimes crosscutting them. The disruptive nature of the hoppers in the Ellicott

Creek Breccia, for example, suggests that they formed within the sediment rather than at the air- water interface, and that organic remains might have acted as nucleation points for developing halite crystals. To explain these associations, we present a preservational model in which displacive salt hoppers formed within NaCl-saturated groundwater as a result of surface evaporation in the vadose zone during regressive phases, and only after eurypterid remains were buried. In this scenario, the intimate association of eurypterids and salt hoppers in these deposits reflects early-stage diagenetic overprinting rather than conditions during life. This model largely negates any hypothesis, based on co-occurrence with salt hoppers, that eurypterids were halotolerant organisms and we conclude that eurypterids preserved in upper Silurian carbonate ramp deposits were primarily denizens of more normal marine subtidal settings.

71

INTRODUCTION

The habitats of the Eurypterida (Arthropoda: Chelicerata) have long been disputed.

Although there now appears to be a consensus that eurypterids underwent a marine-to-freshwater transition during the Late Ordovician–Devonian (Lamsdell and Braddy 2010; see O'Connell

1916; Plotnick 1999; Braddy 2001, for reviews), the preferred habitat and salinity tolerance of many individual groups during this period remain unresolved. Recent work has refined our view of the taxonomic basis for this transition into terrestrially-dominated settings (Lamsdell and

Braddy 2010), but a lack of constraint on the habitat range of many eurypterid lineages remains.

Without these basic paleoecological details, it is difficult to ascertain not only the drivers behind this environmental transition, but also the drivers of eurypterid extinctions that began in the end of the Silurian and culminated in the end-Devonian mass extinction (Lamsdell and Braddy

2010).

Among the transitional taxa are eurypterids from the upper Silurian–Lower Devonian

Salina, Bertie, and lowest Helderberg groups of the Appalachian basin of Laurentia. Here, abundant and well-preserved eurypterids and other fauna are frequently found in calcareous shales and argillaceous, chemically precipitated dolomites (“waterlimes”), deposited in what is generally considered to represent the subtidal–supratidal zone of a shallow lagoonal or sabkha- like environment on the margin of a gently dipping epeiric sea (Ciurca 1973; Smosna et al.,

1977; Belak 1980; Hamell 1982; Tollerton and Muskatt 1984; Ciurca 1990; Bell and Smosna,

1999). Despite general agreement on the depositional environment, determination of the specific paleosalinity (i.e., brackish [hyposaline], normal marine [euhaline], or hypersaline–briny) and eurypterid habitat in these settings is complicated by the co-occurrence of eurypterids with putative terrigenous flora, and normal marine and euryhaline fauna (Tollerton 1997, and

72

references therein; Plotnick, 1999, and references therein; SJC, personal observations; Braddy,

2001; Burrow and Rudkin 2014; McKenzie 2014; Nolan 2014; Chapter II), in units that frequently either lack defining sedimentology at the bed level (cf. Alling and Briggs 1961;

Leutze 1961) or contain indicators of extreme hypersalinity, i.e., evaporitic salt hoppers (Ciurca and Hamell 1994).

Because halite structures are formed under evaporative, hypersaline conditions (Dellwig

1955; Arthurton 1973; Southgate 1982), their intimate association with eurypterids in these beds has led to the assertion by some authors that eurypterids (and other early chelicerates, e.g., scorpions; Kjellesvig-Waering 1966) found in these nearshore deposits probably inhabited these conditions, and/or were euryhaline (e.g., Clarke and Ruedemann 1912; Alling and Briggs 1961;

Størmer 1976; Kluessendorf 1994; see Braddy 2001). However, implicit within this view is the requirement that eurypterids tolerated far higher salinities than any modern marine chelicerate.

In this study, we aim to determine the likelihood for eurypterid inhabitance, or burial, in hypersaline environments by examining the depositional relationship of eurypterids and salt hoppers at several stratigraphic scales, from locality to regional-level. Surveys of eurypterid-salt hopper associations provide empirical evidence for the respective timing of eurypterid burial and associated evaporite formation, and whether or not these structures should be considered indicative of habitat salinity. Based on these results, we present a new depositional model to explain the co-occurrence of eurypterids and evaporites in the Appalachian basin, and discuss its implications for eurypterid life habitats and preservation in the mid-Paleozoic.

73

GEOLOGIC SETTING

Appalachian Basin Stratigraphy

Laurentian epicontinental seas during the mid-Paleozoic were frequently evaporitic

(Rickard, 1969). In the Appalachian basin, restriction from oceanic marine input, a low latitude position, and a warm, arid climate led to the formation of evaporite deposits often hundreds of meters thick in the basin depo-center (Alling and Briggs 1961; Dennison and Head 1975;

Smosna et al. 1977; Van der Voo 1988). These evaporite deposits are represented by subsurface formations in the Salina Group lettered A–F (Rickard 1969). Nearshore carbonate ramp environments in the northern Appalachian basin (New York and Ontario) are represented by exposures in the Syracuse and Camillus Formations (Salina Group) and the entire Bertie Group

(Fig. 1). To the south, in Pennsylvania, Maryland, and West Virginia, this ramp setting is represented by the more argillaceous Wills Creek and Tonoloway Formations (Tourek 1970 unpublished; Bell and Smosna 1999). The Bertie Group contains none of the thick evaporite deposits seen in the Salina Group and, evidently, the basin was less prone to significant evaporite formation than it had been during Salina deposition. However, the basin still became hypersaline or briny during Bertie Group deposition, as indicated by the presence of thin evaporite layers such as the gypsum beds in the Forge Hollow Formation, and various evaporitic structures

(Tollerton and Muskatt 1984; Ciurca and Hamell 1994).

Paleosalinity

Paleosalinity in the carbonate ramp settings of the upper Silurian Appalachian basin has been interpreted as ranging from brackish to hypersaline or briny. Brackish conditions are

74

usually inferred from circumstantial evidence such the presence of terrestrial flora, a paucity of euhaline marine fauna and bioturbation, and the presence of apparently euryhaline, hyposaline- tolerant taxa such as gastropods, brachiopods, ostracods, and leperditicopid arthropods (e.g.,

Kjellesvig-Waering 1950; Leutze 1961; Plotnick 1999; Vannier et al. 2001; Edwards et al. 2004;

Chapter II). Lingulate brachiopods are often found with eurypterids and are suggestive of eu- or hyposalinity as none have been identified in unequivocally hypersaline settings. The extinct -like arthropod Leperditia is particularly abundant in some mid-Paleozoic eurypterid assemblages, and also thought to have been both highly halotolerant and resistant to desiccation

(Vannier et al. 2001). However, the frequency at which leperditicopids are found in isolation on bedding planes within subaerially exposed sabkha-like intertidal–supratidal zones (e.g., in the

Tonoloway Formation; Smosna et al. 1977; Warshauer and Smosna 1977; Chapter II) suggests that they were more tolerant of evaporative conditions than other contemporaneous arthropods, including eurypterids. Eurypterids themselves have previously been used as indicators of hyposalinity in some settings, but it has since been argued that, in the absence of other sedimentological evidence, such interpretations may be erroneous because of their euryhaline tendencies (Selden 1984; Braddy 2001).

Unlike brackish conditions, hypersalinity in Appalachian basin nearshore deposits is unequivocally indicated by evaporitic structures such as gypsum beds, casts, and vugs, salt hoppers or halite molds/casts, and desiccation features, e.g., desiccation cracks, that occur throughout the Salina Group and suprajacent Bertie Group (Hamell 1982; Hamell and Ciurca

1982; Tollerton and Muskatt 1984; Ciurca and Hamell 1994). Salt hoppers and early-stage halite molds/casts (i.e., flat-faced cubic halite impressions lacking the characteristic hopper shape; see below) are among the most common sedimentary features in these intervals and both types of

75

structure frequently occur on the same bedding planes as eurypterids (Tollerton and Muskatt

1984; Ciurca and Hamell 1994; Ciurca 2013; see below), sometimes even crosscutting them or other organic structures. This close eurypterid-evaporite association has led some authors to suggest that pervasive hypersalinity may have been conducive to the excellent preservation of eurypterids and other fauna in the Bertie Group (Leutze 1961; Kluessendorf 1994; Edwards et al.

2004; Vrazo and Braddy 2011; Ciurca 2013). Although he was unwilling to make any definite claims regarding eurypterid salinity tolerance, Leutze (1961) went as far as to suggest that high salinity in the Salina Group may have occasionally created a “pickling brine”, preserving tissue that was otherwise unlikely to survive bacterial degradation. Because of the particularly close association of salt hoppers with eurypterids, we will focus on their development below.

Salt Hopper Development

Salt hoppers are hopper-shaped crystalline structures made from evaporitic minerals

(halite) that occur in both ancient and modern settings. The term “hopper” refers to the stepped, pyramidal shape that is formed as the mineral precipitates outward from the edge, rather than center, of a crystal core. Salt hoppers are only one of several types of halite structure that have been found in Laurentian evaporite deposits and should not be confused with chevron halite, for example (Dellwig 1955; Arthurton 1973). Hopper-shaped halite crystals have been shown to form experimentally both at the air-water interface in saturated sodium chloride (NaCl) brines

(Dellwig 1955; Arthurton 1973; Southgate 1982) and within the water column (Sloss 1969) as a result of surface evaporation. In the field, these are traditionally interpreted as having formed in evaporitic brine pools (e.g., Southgate 1982). If halite crystals, either as an isolated hopper or as part of a floating crystalline raft, become too large to be kept buoyant by surface tension, they

76

will drop down to the substrate and continue to grow as bottom growth crystals if the water column is completely saturated (Dellwig 1955). Salt hoppers may also grow within the sediment if sodium chloride-saturated brines laterally penetrate the phreatic or vadose zone of subaerially exposed deposits (Gornitz and Schreiber 1981). Evidence for displacive intrasedimentary salt hopper growth in the subsurface has been noted in modern or sub-Recent basins (Gornitz and

Schreiber 1981), sabkhas (Shearman 1978), and salt pans and lakes (Handford 1982; Lowenstein and Hardie 1985), and in ancient marine sediments (Leitner et al. 2013).

Salt Hoppers in the Appalachian Basin

In Silurian surface exposures in the Appalachian basin, salt hoppers appear to always be replaced by a relic, pseudomorph mold, or cast, that retains the “hopper” or pyramidal shape of the original crystal structure (e.g., Fig. 2). Salt hoppers in subsurface exposures, however, can retain their original halite composition (SJC, personal observation). The color of the infill of many salt hopper pseudomorphs ranges from bright orange to purple-red, indicating incorporation of iron at the time of formation or during subsequent replacement (Dellwig 1955;

Ciurca and Hamell 1994) (Fig. 2A–C). Other salt hopper pseudomorphs are metallic or white, having been replaced with hematite, dolomite, or quartz, respectively (e.g., Fig. 2D–E).

Unaltered salt hoppers are entirely absent from any exposures examined in this study and thus we will refer to pseudomorph casts or molds simply as salt hoppers herein.

The salt hoppers found in the eurypterid-bearing units in the upper Silurian units of the

Appalachian basin are notable both for their size, some growing upward of 30 cm (Ciurca and

Hamell 1994), and their isolated nature. Unlike those that are found as part of the thick and widespread evaporite beds that are found in the subsurface Salina Group (e.g., Dellwig 1955),

77

salt hoppers in surface exposures, for example, in the Phelps Waterlime Member (PWM) at Neid

Rd. Quarry, NY, appear sporadically within a dolomitic matrix. Based on current models, these salt hoppers developed either: 1) at the brine surface, and subsequently dropped to the bottom once they became larger, as suggested by Dellwig (1955) for some larger salt hoppers in the

Michigan basin, 2) as isolated bottom-growth crystals on the substrate (cf. Dellwig 1955;

Arthurton 1973), or 3) interstitially within the sediment (cf. Gornitz and Schreiber 1981; see below).

Salt Hopper-Eurypterid/Organismal Associations

The observation that eurypterids are closely associated with evaporites in the upper

Silurian was made early in the study of this group (e.g., Clarke 1907). Subsequent authors have considered the possible eurypterid occupation of hypersaline or briny environments in the context of eurypterid paleoecological trends during the Paleozoic (e.g., Clarke and Ruedemann

1912; O'Connell 1916; Kjellesvig-Waering 1961; Størmer 1976; Plotnick 1999; Braddy 2001), but comparatively little attention has been given to the physical co-occurrence of evaporitic structures and eurypterids. Tollerton and Muskatt (1984) provided an in depth review of sedimentary structures in the Bertie Group, including evaporites. They inferred that halite crystals may have formed at very shallow depths in this environment, but left open the question of water depth and did not specifically consider salt hoppers in relation to eurypterid inhabitation or preservation. The only documented example of a close eurypterid-salt hopper association in the Salina Group was by Ciurca (1990; personal observation), who found salt hoppers and eurypterids in the same horizon, including a salt hopper disrupting a fossil exoskeleton, in what he termed the Barge Canal Member of the Vernon Formation (located above Sarle’s [1903]

78

“Pittsford shale” eurypterid assemblage [cf. Hartnagel 1903]). In the Bertie Group, Ciurca (2005,

2011, 2013) and Ciurca and Hamell (1994) documented examples of salt hoppers that cross-cut various organisms. In the Moran Corner Waterlime Member, Ciurca collected a eurypterid that had been disrupted by a salt hopper (Fig. 3A). In the Fort Hill Waterlime (Oatka Formation),

Ciurca (2011, fig. 1) highlighted a microbial mound (thrombolite?) growing on top of a salt- hopper-bearing dolomite and a rare disruptive salt hopper growing within a thrombolite (Fig.

3B). In the Ellicott Creek Breccia (ECB), Ciurca (2013, fig. 17) documented a large salt hopper on the same bedding plane as eurypterid remains. From the Williamsville Formation, Ciurca found an example of a small salt hopper displacing what may be a microbial mat (Fig. 3C) and collected slabs containing cephalopods with putative salt hoppers growing either within, or adjacent to them (Ciurca 2010, fig. 36; Fig. 3D).

EURYPTERID AND CHELICERATE PHYSIOLOGY

Testing any hypothesis that eurypterids occupied hypersaline environments first requires assessment of the likelihood that eurypterid remains in these settings represent some sort of autochthonous assemblage, contemporaneous with the evaporite evidence, and available physiological evidence for halotolerance. A variety of taphonomic and stratigraphic evidence indicates both that eurypterids were regular inhabitants of upper Silurian nearshore carbonate settings in which they are found (rather than products of periodic storm deposition, but see

Andrews et al., 1974) and that they were regionally widespread (rather than isolated within

“pools”, cf. Clarke and Ruedemann 1912). The evidence includes results from a taphonomic census (Tetlie et al. 2008), the unsorted size-frequency distribution of eurypterid populations

(Kaneshiro 1962 unpublished; Andrews et al., 1974; Vrazo and Braddy 2011; Chapter II), the

79

regular preservation of very small (juvenile) eurypterid instars, often with adults (cf. Clarke and

Ruedemann 1912; Ruedemann 1925; MBV, personal observation), the continuous occurrence of some taxa within exposures across large geographic distances (up to hundreds of miles) (SJC, personal observations), and the cyclic recurrence of Bertie Group eurypterid assemblages within similar dolomitic facies (Ciurca 1973).

In contrast, physiological evidence for eurypterid and chelicerate occupation of hypersaline environments is less compelling. The only documented eurypterid adaptation to hypersalinity comes from Tylopterella (Tylopterus) boylei, which is known from only one specimen from the Guelph Formation of New York (Clarke and Ruedemann, 1912). Clarke and

Ruedemann (1912, p. 218) (and, later, Kjellesvig-Waering 1958) suggested that the thickened cuticle of this rare taxon was evidence for its inhabitation of “very saline water”. However, the lack of this character in other eurypterid taxa that occur in hypersaline settings suggests that either the interpretation of the cuticle’s purpose, or the proposed depositional environment, is incorrect. Recently, Lamsdell et al. (2009) and Lamsdell and Braddy (2010) suggested more convincingly that the large body size and thick exoskeletal cuticle of giant hibbertopterids in the late Paleozoic were adaptations toward brackish or freshwater habitats, leaving open the question of physiological adaptations to hypersalinity.

In a broader paleoecological context, evidence for eurypterid inhabitance of hypersaline conditions is similarly equivocal. Kjellesvig-Waering’s (1961) once generally accepted “phase” model that grouped eurypterid taxa based on their apparent environmental preference (e.g., the

Eurypteridae occurred in restricted environments prone to hypersalinity), has since been shown to be oversimplified (Braddy 2001). No single taxon or group shows a consistent preference for hypersaline settings. Those taxa that appear most frequently in hypersaline nearshore settings in

80

the upper Silurian also appear in less extreme settings elsewhere. These include: Eurypterus, which has been found as part of a normal, open marine death assemblage (Lamsdell 2011); dolichopterids, which have been found in both brackish or near normal marine environments

(Kjellesvig-Waering and Leutze 1966; Chapter II); and the large pterygotids, which are frequently found alongside Eurypterus in hypersaline deposits but are thought to have been capable of traversing open (Tetlie 2007).

Examination of halotolerant capabilities in modern analogs also does not support eurypterid inhabitation of hypersaline environments. Xiphosurids are the extant marine chelicerate clade most closely related to eurypterids and have traditionally been used for comparison in studies of eurypterid paleoecology and physiology. In their natural habitats, modern xiphosurids such as Limulus polyphemus are euryhaline and can tolerate brackish–mildly hypersaline conditions (Shuster 1982). Ehlinger and Tankersley (2004) showed experimentally that larval Limulus populations can tolerate salinities up to 70 ppt, but begin to decline in higher salinities (i.e., 80 ppt; “penesaline” brines). Limulus also appears to become less halotolerant as it ages and no limulid species is known to occupy briny bodies of water at any growth stage in natural habitats. Following Waterston’s (1979) observation that decapod are increasingly halotolerant in warmer climates, Selden (1984) suggested that eurypterids may have had a wider salinity range than xiphosurids, particularly in the lower, warmer latitudes of

Laurentia. Although Ehlinger and Tankersley (2004) did find an increase in halotolerance in larval Limulus when subjected to increased temperatures, viable salinity levels remained beneath that of brines and well beneath the salinity level required for halite evaporite production (~350 ppt; Scruton 1953).

81

ANALYSIS OF EURYPTERID-EVAPORITE ASSOCIATIONS

To assess the frequency of eurypterid-evaporite associations quantitatively, fieldwork was carried out from 2012-present at a number of key localities across the Appalachian basin: from the south (e.g., Bass, WV), to the north (e.g., Litchfield, NY), and through exposures to the west

(e.g., Ridgemount Quarry, ON). Observations made in the field were combined with additional field notes made by one of us (SJC) to create a comprehensive picture of bed-level occurrences of eurypterids and evaporitic structures within a regional stratigraphic context. To supplement field observations, surveys of eurypterid-salt hopper associations were carried out at the locality- specific scale, and at the regional scale.

Locality-Specific Survey

Specimens from the ECB of the Fiddlers Green Formation (Bertie Group) of southwestern Ontario were surveyed for salt hopper-eurypterid associations. This unit was chosen because of the large number of eurypterids that have been collected from this interval by

SJC (>800) from a single locality (Ridgemount Quarry, near Ft. Erie, ON; 42°92'N/79°00'W), the presence of salt hoppers throughout the unit, and its traditional interpretation as a hypersaline environment (e.g., Ciurca 2013). The ECB is a roughly three-meter thick dolomitic unit deposited within the subtidal-intertidal zone of a shallow carbonate ramp. The “breccia” refers to a collapsed breccia layer that is found in the upper ECB throughout its exposure (southwestern

Ontario to western New York), which is either the result of evaporite dissolution, a seismite, or both (cf. Ciurca 2011). Eurypterids are found throughout the ECB, but occur predominantly within the lower and middle sections of the unit within large microbial/ thrombolitic beds that

82

Ciurca (2011) refers to as a topographic waterlime.

Specimens collected from the ECB and examined in this study were predominantly

Eurypterus cf. remipes, with a smaller number of E. cf. laculatus (cf. Tetlie 2006). Other taxa known from this interval include dolichopterid, pterygotid, and carcinosomatid eurypterids, as well as athyrid brachiopods (Nucleospira), nautiloid cephalopods (Hexameroceras), and unidentified ostracods or leperditicopids (MBV, personal observation). Most Eurypterus in the

ECB are represented by isolated carapaces; complete or partially articulated examples are rare.

Several specimens of Eurypterus cf. remipes used in this study were collected in the field in the summer of 2014, but the majority of specimens are housed at the Yale Peabody Museum in the

Ciurca Collection. This collection contains over 10,000 specimens of eurypterids collected by one of us (SJC) from the 1960s to the present. SJC typically collected all eurypterid specimens

(including disarticulated and isolated fragments), as well as associated fauna and sedimentary structures, from a given locality. Thus, the breadth of this collection and generally limited collector bias permit detailed censuses of eurypterid remains to be made (Tetlie et al.

2008; Chapter II).

Region-Wide Survey

For a regional picture of eurypterid-salt hopper associations, we surveyed all known eurypterid- producing units of Late Ordovician to Early Devonian-age in the Appalachian basin region (i.e., eastern Ohio/southwestern Ontario to easternmost-central New York; northern New York to southwestern West Virginia and western Maryland). We restricted our survey to this region because of the particularly detailed stratigraphic data, often to the bed level, that have been recorded here at multiple localities across a wide geographic range. Collected locality data

83

include bed-level lithology, presence of microbial structures, and presence of evaporitic structures. These data were collated from field observations, extensive field notes made by one of us in the Appalachian basin (SJC), and the primary literature. For all localities surveyed, the position of eurypterids within a given unit was resolved to the bed level. When multiple localities exposed the same eurypterid-bearing unit, we counted this as a single occurrence. These data, plus taxonomic data, form part of a larger ongoing study of eurypterid Lagerstätten preservation in the mid-Paleozoic (cf. Vrazo et al. 2014a).

RESULTS OF EURYPTERID-EVAPORITE SURVEYS

Locality-Specific Results

In the survey of eurypterids from the Ellicott Creek Breccia Member in the Ciurca

Collection, 479 specimens were examined. Virtually all examined specimens were isolated carapaces, with only a handful of partially or nearly fully articulated specimens present. Of those specimens examined, 2% (n = 11) contained either obvious salt hopper structures or evidence for early-stage skeletal halite growth (e.g., Fig. 4A–F). The degree of salt hopper disruption of the specimen depends on the size of the halite crystal, but most hoppers we observed crosscutting eurypterids were small, i.e., <1 cm, compared to the maximum size of isolated hoppers observed in the collection (~5 cm). All observed salt hoppers appeared to be isolated, rather than part of a larger evaporitic raft or mat, and these were generally similar in size and morphology to those that have been previously documented crosscutting eurypterids or other organic material (e.g.,

Fig. 3A, C). Larger, more developed salt hoppers occur primarily in the middle of a given specimen (i.e., near the center of the carapace), whereas incipient evaporite growth seems to occur primarily around carapace margins, resulting in highly disrupted specimens (e.g., Fig. 4A,

84

F). Other than fine (microbial?) laminations, no other identifiable sedimentary or evaporitic structures were found in close association with the examined eurypterid remains. Closely associated fauna were largely absent, with the exception of an occasional putative Leperditia impression. It should be noted that most eurypterid-bearing slabs in the Ciurca Collection were cut down to retain only the eurypterid-bearing portion (MBV, personal observation); therefore, it is possible that some specimens were originally found proximal to salt hoppers (i.e., within a few centimeters).

Region-Wide-Results

In the survey of all Late Ordovician to Early Devonian-age units in the Appalachian basin, 51 stratigraphic intervals (formation-level or lower) were found to contain eurypterid remains. A majority of these (n = 30) were late Silurian-age, of which 70% (n = 21) occurred within the Bertie Group. Twenty-eight surveyed units contained evaporites and 19 (68%) of these contained eurypterids. In other words, 37% (19:51) of all surveyed eurypterid-bearing units contained evaporites (salt hoppers) in the same bed as eurypterid remains (see Appendix, Chapter

III Fig. 1 for a locality map).

The survey results also reveal that the close associations of evaporites and eurypterids are phenomena that are restricted chronostratigraphically to the late Silurian and regionally to the northern basin. With the exception of one occurrence in the Wenlock-age Eramosa Formation

(Lockport Group; formerly the Oak Orchard Formation, cf. Ciurca 1990), all intervals containing both salt hoppers and eurypterids were of late Silurian age, beginning in the late Ludlovian

Vernon Formation and ending in the end-Přídolí–earliest Lochkovian? Honeoye Falls Formation.

All formation-level intervals within the Bertie Group of New York and Ontario contain both

85

eurypterids and evaporites in close association, with the exception of the Forge Hollow and

Akron Formations, which contain evaporites but no eurypterids. In the subjacent Salina Group, the Syracuse and Vernon Formations show similar eurypterid-salt hopper associations. No eurypterids are known from the subsurface Syracuse Formation A–F evaporite members, and eurypterids are completely absent from exposures of the highly evaporitic Camillus Formation.

In the central Appalachian basin (Pennsylvania), late Silurian eurypterids occur in similar carbonate facies (represented by the Tonoloway Formation) as those to the north, but although evaporites are present in some beds here, none closely co-occur with eurypterid remains (Chapter

II). No eurypterid-salt hopper associations are known from the upper Silurian Tonoloway or

Wills Creek Formations in the southern Appalachian, despite the prevalence of eurypterids in some beds (Kjellesvig-Waering 1950; Kjellesvig-Waering and Leutze 1966; MBV, personal observation).

Evaporite-eurypterid associations in the Appalachian basin appear to be entirely restricted to dolomitic facies, usually massive waterlimes, with the exception of those found in the Vernon

Formation, where they occur in thinly laminated black shales. Salt hoppers or early-stage halite molds/casts are the sole evaporitic structure found closely associated with eurypterids. Other evaporitic structures such as relict halite casts/molds or vugs, or chevron halite, were occasionally present in adjacent beds, but none were found on the same bedding plane as eurypterids. Microbial mounds such as stromatolites and thrombolites, or microbially laminated sediments, were the most common sedimentary structure associated with eurypterids. This frequent co-occurrence has been noted previously by Ciurca (e.g., 2013) and will be discussed further in Chapter IV. Other sedimentary structures (e.g., ripple marks, cross-bedding, bioturbation) in eurypterid-bearing units were rarely observed. Desiccation cracks occur in some

86

intervals, but rarely on the same bedding plane as eurypterids; in the only two examples known, both appear to be the result of post-burial superimposition, rather than contemporaneous formation. Syneresis cracks were absent from examined eurypterid-bearing horizons, although they may be present in adjacent beds.

Some evidence exists for regional variations in salt hopper size and presence within the eurypterid-bearing beds of the Fiddlers Green and Williamsville formations. The coeval ECB and

PWM of the Fiddlers Green formation both contain salt hoppers; however, they are smaller in the

ECB of Ontario–western New York compared to the PWM of central New York. The ECB also lacks the desiccation cracks of the latter member. A second, more localized example occurs in the

A Member of the Williamsville Formation in western New York and southwestern Ontario. No salt hoppers are known from exposures in Buffalo, New York, and are abundant there, whereas only 22 km to the west at Ridgemount Quarry, Ontario, rare salt hoppers are present and

Lingula are absent.

Beyond the Appalachian basin to the west, there are a number of eurypterid-bearing units contemporaneous to the Salina and Bertie groups that contain similar dolomitic and/or evaporitic facies, e.g., the Pointe aux Chenes Formation of Michigan, the Bass Islands Group of Ohio and

Michigan, the Tymochtee and Greenfield formations of Ohio (Landes et al. 1945; Leutze 1958;

Alling and Briggs 1961; Stumm and Kjellesvig-Waering 1962), and the Kokomo Limestone

Member (Wabash Formation) of Indiana (Clarke and Ruedemann 1912; Kluessendorf 1994;

Kilibarda and Doff 2007). However, we are not aware of any documented examples of eurypterids co-occurring with evaporites at the bed level in any of these intervals. If the survey is extended to include all Laurentian eurypterid occurrences, the earliest (and only additional) example of a close eurypterid-halite evaporite association on the same bedding plane is found in

87

the Upper Ordovician of Manitoba (Young et al. 2007; G.A. Young, personal communication 2014), which has been interpreted as having a Bertie-like depositional environment.

DISCUSSION

Salt hoppers in eurypterid-bearing units in the Salina and Bertie Groups appear to be predominantly displacive, i.e., they completed development on the sediment surface, or interstitially within supersaturated subsurface sediments, rather than at the air-water interface or in the water column in bodies of brine as in the model proposed by Dellwig (1955) and others.

This type of growth is supported by the observation that many salt hopper structures crosscut laminated sediments and biogenic substrates (i.e., thrombolites; Fig. 3B), and the presence of evaporitic dendrites, which cut through the surrounding and presumably uncompacted matrix

(Fig. 2A–B). Such crosscutting indicates that development of the hopper structure was completed only following deposition of the surrounding sediments or biogenic material. Growth either on or in the sediment is further supported by the large size of many hoppers, which were probably not capable of remaining buoyed at the air-water interface, or in the water column, based on experimental results (cf. Dellwig 1955; Arthurton 1973) (e.g., Fig. 2C–E). In considering the question of whether salt hoppers associated with eurypterids began their initial growth at the air- water interface, only to complete development on or in the sediment surface, or began and completed their growth entirely within the sediment, the following suggests the latter. Neither relict halite raft structures (suggestive of buoyed crystal growth on the brine surface; Dellwig

1955; Shearman 1970; Arthurton 1973), nor syntaxial crystal overgrowths (suggestive of halite growth on the sediment surface; Dellwig 1955; Lowenstein and Hardie 1985), have been

88

observed in eurypterid-bearing beds. Furthermore, the regular confinement of salt hoppers or their incipient forms to within the specimen periphery, rather than adjacent to them, suggests to us that growth of these structures may have only commenced following deposition of the specimen on or in the substrate; i.e., eurypterids and other organic structures might have acted as nucleation points for halite development following burial. Considering the available evidence, it seems plausible that salt hopper growth in eurypterid-bearing beds largely occurred within the sediment, rather than in the water column, and only after burial of the eurypterids themselves. In turn, it can be inferred that salt hopper formation and burial of eurypterid remains were not concurrent events. But were the eurypterids themselves buried under hypersaline conditions?

The pervasiveness of salt hoppers, gypsum molds, and other evaporitic structures in the dolomitic units of the upper Silurian Appalachian basin indicate that this region was particularly prone to evaporite deposition. Dolomite is the first evaporite to precipitate out of solution when salinity rises above ~70 ppt (Scruton 1953). In the context of the circulation restricted and arid

Appalachian basin, it is plausible that the water column regularly became saturated in CaCO3 and Mg, leading to the formation of evaporitic primary dolomite, or post-depositional penecontemporaneous dolomite. Halite evaporites only occur at salinity levels at ~350 ppt and above and, thus, under this evaporitic regime, the prevalence of salt hoppers within dolomitic units containing eurypterids and other fauna would seem to indicate that organismal burial took place under extremely hypersaline/briny conditions. In the Bertie Group, primary or penecontemporaneous dolomites have been interpreted in some eurypterid-bearing intervals, such as in the PWM (Andrews et al. 1974). Although early post-depositional penecontemporaneous dolomitization cannot be ruled out, two pieces of evidence suggest that dolomite precipitation was probably not syndepositional with organism burial. Firstly, a diverse

89

fauna that includes is found in one of the most prolific eurypterid-bearing waterlimes, the A

Member of the Williamsville Formation (Burrow and Rudkin 2014; Ciurca, personal observation). This indicates that salinity conditions at the time of deposition were probably near normal marine or hyposaline. Belak (1980) noted a similarly stenohaline and subtidal fauna in certain dolomites of the suprajacent Cobleskill and Akron Formations and suggested that this negated the possibility of penecontemporaneous dolomitization in those intervals. Belak suggested instead that magnesium-rich brines saturated the limestones in the intertidal–supratidal zones of the Cobleskill and Akron shoreface following sea level regression. Secondly, formation of penecontemporaneous dolomite following organism burial, or even secondary dolomitization of sediments, is supported by fossil alteration throughout upper Silurian units in the Appalachian basin. Mineralized organisms (e.g., gastropods, cephalopods, bivalves, and brachiopods) found in waterlimes and calcareous shales from the Bertie Group and coeval intervals (e.g., the

Tonoloway Formation) are usually represented by molds or as infilled voids, rather than their original calcareous exoskeleton. If we conclude that the dolomitic eurypterid-bearing waterlimes of the Bertie Group were probably not formed as primary dolomites under evaporative conditions at the air-water interface, this suggests that the interbedded evaporites may have also formed under a different type of evaporitic regime.

Model for Intrasedimentary Salt Hopper Development

The proposed intrasedimentary formation of disruptive salt hoppers in the upper Silurian

Salina and Bertie groups described above requires a developmental pathway dependent primarily on NaCl-saturated groundwater, rather than surface brines. In their description of displacive salt hoppers in sub-Recent Dead Sea sediments, Gornitz and Schreiber (1981) proffered two possible

90

pathways for intrasedimentary salt hopper growth in a muddy substrate. Concentrated brines either: a) diffused downward into submerged sediments from the water column, or b) diffused upward though the interstitial space of the capillary fringe following vadose zone exposure to air.

Both pathways allow for development of hopper-shaped halite crystals in the sediment, but differ in terms of evaporation taking place over subaqueous or subaerially exposed sediments, respectively. Eurypterids in the Salina and Bertie groups regularly occur within cyclic, shallowing-upward successions whose uppermost beds show evidence for subaerial exposure

(e.g., the extensive desiccation cracks of the PWM), but lack evaporites. Thus, in considering

Gornitz and Schreiber’s pathways for intrasedimentary salt hopper formation, it seems more likely that salt hoppers in these units were formed via upward diffusion of brines during a regressive phase, whereby saturated fluids laterally permeated the subsurface as evaporation drove upward migration of the brines through capillary space of air-exposed sediment in the vadose zone. However, we cannot rule out that salt hoppers and other evaporites in some units may have formed via downward diffusion of supersaturated brines into the sediment from shallow evaporitic pools. This latter pathway may explain the barren dissolution breccia in the uppermost beds of the ECB, for example.

Basin topography also supports this proposed sequence of events leading to close eurypterid-salt hopper associations. The slope of the carbonate ramp in the upper Silurian

Appalachian basin was extremely gentle (Belak 1980; Bell and Smosna 1999) and during regressive phases, sea level and the height of the water table would have shifted in elevation very gradually along the shallow slope, creating prolonged periods of surface and groundwater stagnation in the intertidal–supratidal vadose and phreatic zones, respectively. In conjunction with regression, surface evaporation due to the arid climate and a lack of regular oceanic input

91

would have quickly elevated salinity levels in the basin margin to the point of supersaturation. As the intertidal–supratidal zones became increasingly subaerially exposed and groundwater became briny, halite crystals in the subsurface may have preferentially nucleated on buried organic material such as eurypterid cuticle, leading to the intimate salt hopper-eurypterid relationship we have documented above (Fig. 5).

This regressive pathway for hopper formation may also explain why hoppers are found on multiple horizons within single beds—as sea level dropped, the phreatic zone would have shifted, creating multiple nucleation horizons—as well as the size/abundance variations noted in some intervals. In his study of a sub-Recent playa basin, Handford (1982) noted that the greatest intrasedimentary hopper growth occurred in the subaerial saline mudflat stage, and that salt hopper size appears to reflect growth rates. In considering similar mudflat-sabkha-type settings on the margins of the Appalachian basin (e.g., Smosna et al. 1977; Belak 1980; Hamell and

Ciurca 1982), the large size of salt hoppers in some units such as the PWM in central New York may reflect a slow rate of regression and prolonged development in a subaerially exposed sediment, whereas the smaller hoppers in the ECB to the west may reflect slightly deeper subaqueous conditions. Similarly, the presence of salt hoppers in the Williamsville Formation A

Member of southwestern Ontario, and their absence (and the presence of Lingula) in Buffalo,

New York, seems to suggest the formation of a steep east-west halocline following eurypterid deposition—from hypersaline, to normal marine or even hyposaline, respectively.

Implications for Eurypterid Paleoecology

If our model is valid, this strongly calls into question any hypothesis that eurypterids actively occupied the penesaline or extremely hypersaline conditions of the late Silurian, and

92

reinforces our view that eurypterids preserved in these carbonate ramp settings were primarily denizens of subtidal settings with near normal marine conditions (i.e., from hyposaline to slightly hypersaline). However, if eurypterids avoided the most extreme nearshore settings, this raises a simple but lingering question; Where did eurypterids go when conditions became briny?

Appalachian basin paleogeography suggests that eurypterids moved either inland via or deltas to the east or into more normal marine conditions to the south. For eurypterids in the

“Salina Series” (i.e., most of what is now the Salina and Bertie Groups), Clarke and Ruedemann

(1912) postulated the former, essentially suggesting that this predicated the predominantly freshwater habitat of later Devonian eurypterids (but see O'Connell 1916 for a counterargument).

Early Silurian eurypterid remains from the coeval Tuscarora and Shawangunk Formations of

Pennsylvania and New York, respectively (Smith 1970; Cotter 1983), occur in thin dark shales interbedded within massive conglomeratic arenites (Clarke and Ruedemann 1912; MBV, personal observation) and may represent such inland incursions. Although there is no firm agreement on the depositional environment of these intervals—they were most likely deposited in either a fluvial or estuarine-type deposit, or within a marine-influenced but low-energy back- bar-type setting (Epstein 1993)—they almost certainly were not hypersaline.

Alternatively, if eurypterids ventured into more fully marine settings, the late Silurian

Keyser Formation of Pennsylvania, Maryland, and West Virginia represents a likely depositional environment. The Keyser Formation appears to be contemporaneous with the uppermost Bertie

Group and largely represents a subtidal and normal marine reef environment (Makurath 1977).

This interval also contains intermittent carbonate facies similar to those that contain eurypterids in the Bertie Group, although these have not yet yielded eurypterids. Unequivocal evidence for marine occupation of normal marine environments similar to the Keyser Formation comes from

93

the diverse early Silurian (Llandovery) death assemblage of the Pentland Hills Lagerstätte in

Scotland where eurypterids, including Eurypterus?, are found with euhaline taxa, including a variety of (Lamsdell 2011).

Eurypterid Preservation

In our model of interstitial salt hopper formation in eurypterid-bearing units, we envisage eurypterid burial and salt hopper development as temporally separate and sequential events; salt hopper formation only occurred following burial of eurypterids and contemporaneous fauna.

This temporal gap between eurypterid burial and evaporite formation would preclude their preservation in Leutze’s (1961) “pickling brine”—although if evaporitic brines began percolating downward within a few centuries after eurypterid burial, they may have aided in long-term preservation. If any evidence for in situ eurypterid pickling exists, it may come from the Upper

Devonian Osovets beds of the Starobin potassium-salt basin in Belarus where several stylonurid specimens have been collected from thin clay bands interbedded within thick sylvinite deposits

(Plax and Barbikov 2009).

Slight to moderate (sub-evaporitic) hypersalinity in the water column, on the other hand, may have played a more immediate, if less evident role in eurypterid preservation. Increases in temperature and salinity reduce aquatic oxygen concentrations (Warren 2006). Evaporation in the

Appalachian basin would have been capable of driving salinity to beyond habitable levels and establishing concomitant dysoxic or anoxic conditions that typically exclude bioturbators and biodegraders (e.g., Fig. 5B). In this stagnant environment, the likelihood of eurypterid cuticle and other soft-tissue organism (e.g., early plants, worms) preservation would increase

(Kluessendorf 1994; Edwards et al. 2004; SJC personal observation). This combination of

94

hypersaline brines and anoxia as a preservational agent for arthropod cuticle has been cited elsewhere in Recent (Mutel et al. 2008; Parsons-Hubbard et al. 2008) and ancient aquatic environments (Barthel et al. 1990).

Beyond the Appalachian basin, within Laurentia and elsewhere, our preservational model is likely to be applicable to other carbonate ramp settings in which eurypterid faunas occur in nearshore dolomitic and evaporitic facies. For example, in the Bertie-like Late Ordovician Stony

Mountain Formation Lagerstätte in Manitoba, Canada, G.A. Young (personal communication

2015) has suggested that halite associated with eurypterids may have formed post-burial.

Similarly, in the Silurian of Baltica and the Ukraine, where a eurypterid fauna comparable to that of the Bertie Group is found in a similar depositional environment (Viira and Einasto 2003;

Meidla et al. 2014; SJC, personal observation), preservation probably occurred in a similar manner.

CONCLUSIONS

Past interpretations of eurypterid habitats in the late Silurian Appalachian basin were often a byproduct of inferred depositional environment at coarse stratigraphic scales. Inclusion of eurypterid-bearing units with barren, evaporitic deposits led to generalizations regarding paleosalinity and eurypterid halotolerance. The frequently restricted fauna of the Salina and

Bertie groups has also informed such interpretations of paleoenvironment, although we question the utility of these faunas for interpretations of paleosalinity in the absence of sedimentary evidence. More recently it has become clear that a full understanding of eurypterid paleoecology and preservation in the Appalachian basin and elsewhere can only occur within a revised stratigraphic framework (Brett et al. 1990; Ciurca 1990).

95

From the survey results and the sequence of events in our proposed model, we can make three broad conclusions. Firstly, the margins of the Appalachian basin during the late Silurian were frequently hypersaline, thus reaffirming the long-held view of the regional paleoenvironment at this time. Secondly, and more importantly, the association of eurypterids and salt hoppers appears to be the result of early-stage diagenetic overprinting following deposition, rather than a reflection of conditions in the eurypterid life habitat. Thirdly, eurypterid remains probably reflect burial in very shallow subtidal deposits, rather than transport into intertidal–supratidal settings. From these conclusions, we are able to refute to a large degree the traditional notion that eurypterids occupied hypersaline conditions during the late Silurian. This is significant when considering eurypterid paleoecology and evolution: constraint of the likely eurypterid habitat in the Appalachian basin to near normal marine or hyposaline subtidal settings represents a critical first step in gaining a better understanding of their environmental preference during a transitional time in their history.

ACKNOWLEDGEMENTS

The authors would like to thank Susan Butts and Jessica Utrup (YPM) for their collections assistance. Tim Phillips is thanked for his assistance with figures. The authors would also like to thank Stephen Bell, Ray Garton, Trent Spielman, and Jeffrey Trop for field assistance, specimen collection, and locality discussion. We gratefully acknowledge Graham Young and Peter Van

Roy for their helpful suggestions and thoughtful reviews of this manuscript. This study was supported by grants to MBV from the University Of Cincinnati Chapter Of Sigma Xi, the

Geological Society of America, the Schuchert and Dunbar Grant-in-Aid Program (Yale Peabody

Museum), and the Caster Fund (University of Cincinnati).

96

REFERENCES

Alling, H.A., and Briggs, L.I., 1961, Stratigraphy of upper Silurian Cayugan evaporites: AAPG

Bulletin, v. 45, p. 515–547, doi: 10.1306/bc743673-16be-11d7-8645000102c1865d.

Andrews, H.E., Brower, J.C., Gould, S.J., and Reyment, R.A., 1974, Growth and variation in

Eurypterus remipes DeKay: Bulletin of the Geological Institution of the University of

Uppsala. New Series, v. 4, p. 81–114.

Arthurton, R.S., 1973, Experimentally produced halite compared with layered halite-

rock from Cheshire, England: Sedimentology, v. 20, p. 145–160.

Barthel, K.W., Swinburne, N.H.M., and Conway Morris, S., 1990, Solnhofen: a study in

Mesozoic palaeontology: Cambridge University Press, New York.

Belak, R., 1980, The Cobleskill and Akron members of the Rondout Formation: late Silurian

carbonate shelf sedimentation in the Appalachian basin, New York State: Journal of

Sedimentary Research, v. 50, p. 1187–1204, doi: 10.1306/212f7ba8-2b24-11d7-

8648000102c1865d.

Bell, S.C., and Smosna, R., 1999, Regional facies analysis and carbonate ramp development in

the Tonoloway Limestone (upper Silurian; central Appalachians): Southeastern Geology,

v. 38, p. 259–278.

Braddy, S.J., 2001, Eurypterid palaeoecology: palaeobiological, ichnological and comparative

evidence for a 'mass-moult-mate' hypothesis: Palaeogeography, Palaeoclimatology,

Palaeoecology, v. 172, p. 115–132.

97

Brett, C.E., Goodman, W.M., and LoDuca, S.T., 1990, Sequences, cycles, and basin dynamics in

the Silurian of the Appalachian foreland basin: Sedimentary Geology, v. 69, p. 191–244,

doi: http://dx.doi.org/10.1016/0037-0738(90)90051-T.

Burrow, C.J., and Rudkin, D., 2014, Oldest near-complete acanthodian: The first from

the Silurian Konservat-Lagerstätte, Ontario: PLoS ONE, v. 9, p. 1–9.

Ciurca, S.J., Jr., 1973, Eurypterid horizons and the stratigraphy of upper Silurian and Lower

Devonian rocks of western New York State, New York State Geological Association, 45th

Annual Meeting, Brockport, New York, p. D1–D14.

Ciurca, S.J., Jr., 1990, Eurypterid biofacies of the Silurian–Devonian evaporite sequence:

Niagara Penninsula, Ontario, Canada and New York State, in Lash, G.G., ed., New York

State Geological Association, 62nd Annual Meeting, Fredonia, New York, p. D1–D23.

Ciurca, S.J., Jr., 2005, Eurypterids and facies changes within the Silurian/Devonian "Eurypterid

Beds" of New York State, in Valentino, D.W., ed., New York State Geological

Association, 77th Annual Meeting, Albany, New York, p. 113–121.

Ciurca, S.J., Jr., 2010, Eurypterids Illustrated: The Search for Prehistoric Sea Scorpions:

PaleoResearch, Rochester, New York.

Ciurca, S.J., Jr., 2011, Silurian and Devonian eurypterid horizons in upstate New York, in

Nelson, N., ed., New York State Geological Association, 83rd Annual Meeting, Syracuse,

New York, p. 139–151.

Ciurca, S.J., Jr., 2013, Microbialites within the eurypterid-bearing Bertie Group of western New

98

York and Ontario, Canada, in Baird, G., and Wilson, M., eds., New York State Geological

Association, 85th Annual Meeting, Fredonia, New York, p. 154–179.

Ciurca, S.J., Jr., and Hamell, R.D., 1994, Late Silurian sedimentation, sedimentary structures and

paleoenvironmental settings within an eurypterid-bearing sequence (Salina and Bertie

Groups), Western New York State and Southwestern Ontario, Canada, in Brett, C.E., and

Scatterday, J., eds., New York State Geological Association, 66th Annual Meeting,

Rochester, New York, p. 457–488.

Clarke, J.M., 1907, The Eurypterus shales of the Shawangunk mountains in eastern New York:

New York State Museum Bulletin, v. 107, p. 295–310.

Clarke, J.M., and Ruedemann, R., 1912, The Eurypterida of New York: New York State Museum

Memoir, v. 14, p. 1–439.

Cotter, E.C., 1983, Shelf, paralic, and fluvial environments and eustatic sea-level fluctuations in

the origin of the Tuscarora Formation (lower Silurian) of central Pennsylvania: Journal of

Sedimentary Petrology, v. 53, p. 25–49.

Dellwig, L.F., 1955, Origin of the Salina salt of Michigan: Journal of Sedimentary Research, v.

25, p. 83–110, doi: 10.1306/d4269819-2b26-11d7-8648000102c1865d.

Dennison, J.M., and Head, J.W., 1975, Sealevel variations interpreted from the Appalachian

basin Silurian and Devonian: American Journal of Science, v. 275, p. 1089–1120, doi:

10.2475/ajs.275.10.1089.

Edwards, D., Banks, H.P., Ciurca, S.J., Jr., and Laub, R.S., 2004, New Silurian cooksonias from

99

dolostones of north-eastern North America: Botanical Journal of the Linnean Society, v.

146, p. 399–413, doi: 10.1111/j.1095-8339.2004.00332.x.

Ehlinger, G.S., and Tankersley, R.A., 2004, Survival and development of horseshoe crab

(Limulus polyphemus) embryos and larvae in hypersaline conditions: The Biological

Bulletin, v. 206, p. 87–94.

Epstein, J.B., 1993, Stratigraphy of Silurian rocks in Shawangunk Mountain, southeastern New

York, including a historical review of nomenclature: U.S. Geological Survey Bulletin, v.

1839, p. L1–L38.

Gornitz, V.M., and Schreiber, B.C., 1981, Displacive halite hoppers from the Dead Sea: some

implications for ancient evaporite deposits: Journal of Sedimentary Research, v. 51, p.

787–794, doi: 10.1306/212f7dab-2b24-11d7-8648000102c1865d.

Hamell, R.D., 1982, Stratigraphy, petrology and paleoenvironemntal interpretation of the Bertie

Group (Late Cayugan) in New York: Empire State Geogram, v. 18, p. 37–38.

Hamell, R.D., and Ciurca, S.J., Jr., 1986, Paleoenvironmental analysis of the Fiddlers Green

Formation (late Silurian) in New York state, New York State Geological Association, 58th

Annual Meeting, Ithaca, New York, p. 199–218.

Handford, C.R., 1982, Sedimentology and evaporite genesis in a continental-sabkha

playa basin-Bristol Dry Lake, California: Sedimentology, v. 29, p. 239–253.

Hartnagel, C.A., 1903, Preliminary observations on the Cobleskill (“coralline”) limestone of

New York: New York State Museum Bulletin, v. 69, p. 1109–1175.

100

Kaneshiro, E.S., 1962, Growth patterns in Eurypterus remipes remipes DeKay 1825:

Unpublished MS thesis, Unpublished M.S. Thesis, Department of Geology, Syracuse

University, New York, Syracuse, NY, 37 p.

Kilibarda, Z., and Doff, J., 2007, Mudcracks, bird's-eye, and anhydrite in intertidal/supratidal late

Silurian Kokomo Limestone, Indiana: Proceedings of the Indiana Academy of Science, v.

16, p. 1–10.

Kjellesvig-Waering, E.N., 1950, A new Silurian Hughmilleria from West Virginia: Journal of

Paleontology, v. 24, p. 226–228.

Kjellesvig-Waering, E.N., 1958, The genera, species and subspecies of the family Eurypteridae,

Burmeister, 1845: Journal of Paleontology, v. 32, p. 1107–1148.

Kjellesvig-Waering, E.N., 1961, The Silurian Eurypterida of the Welsh Borderland: Journal of

Paleontology, v. 35, p. 789–835, doi: 10.2307/1301214.

Kjellesvig-Waering, E.N., 1966, Silurian scorpions of New York: Journal of Paleontology, v. 40,

p. 359–375.

Kjellesvig-Waering, E.N., and Leutze, W.P., 1966, Eurypterids from the Silurian of West

Virginia: Journal of Paleontology, v. 40, p. 1109–1122.

Kluessendorf, J., 1994, Predictability of Silurian Fossil-Konservat-Lagerstätten in North

America: Lethaia, v. 27, p. 337–344.

Lamsdell, J.C., 2011, The eurypterid Stoermeropterus conicus from the lower Silurian of the

Pentland Hills, Scotland: Monograph of the Palaeontographical Society, v. 165, p. 1–84,

101

pls 1–15.

Lamsdell, J.C., and Braddy, S.J., 2010, Cope's Rule and Romer's theory: patterns of diversity and

gigantism in eurypterids and Palaeozoic vertebrates: Biology Letters, v. 6, p. 265–269,

doi: 10.1098/rsbl.2009.0700.

Lamsdell, J.C., Braddy, S.J., and Tetlie, O.E., 2009, Redescription of Drepanopterus abonensis

(Chelicerata: Eurypterida: Stylonurina) from the late Devonian of Portishead, UK:

Palaeontology, v. 52, p. 1113–1139, doi: 10.1111/j.1475-4983.2009.00902.x.

Landes, K.K., Ehlers, G.E., and Stanley, G.M., 1945, Geology of the Mackinac Straits region:

Michigan Geological Survey, v. Publication 44, p. Geological Series 37.

Leitner, C., Neubauer, F., Marschallinger, R., Genser, J., and Bernroider, M., 2013, Origin of

deformed halite hopper crystals, pseudomorphic anhydrite cubes and polyhalite in Alpine

evaporites (Austria, Germany): International Journal of Earth Sciences, v. 102, p. 813–

829, doi: 10.1007/s00531-012-0836-6.

Leutze, W.P., 1958, Eurypterids from the Silurian of Ohio: Journal of

Paleontology, v. 32, p. 937–942.

Leutze, W.P., 1961, Arthropods from the Syracuse Formation, Silurian of New York: Journal of

Paleontology, p. 49–64.

Lowenstein, T.K., and Hardie, L.A., 1985, Criteria for the recognition of salt-pan evaporites:

Sedimentology, v. 32, p. 627–644, doi: 10.1111/j.1365-3091.1985.tb00478.x.

Makurath, J.H., 1977, Marine faunal assemblages in the Silurian-Devonian Keyser Limestone of

102

the central Appalachians: Lethaia, v. 10, p. 235–256, doi: 10.1111/j.1502-

3931.1977.tb00618.x.

McKenzie, S.C., 2014, First from the Silurian (Pridolian) Bertie Lagerstätte of New York

State, Geological Society of America, Northeastern Section, 49th Annual Meeting,

Lancaster, PA

Meidla, T., Tinn, O., and Männik, P., 2014, Stop B8: Soeginina cliff, in Bauert, H., Hints, O.,

Meidla, T., and Männik, P., (eds.), 4th Annual Meeting of IGCP 591, Estonia, 10–19 June

2014. Abstracts and Field Guide: University of Tartu, Tartu, Tartu, Estonia, p. 194–196.

Mutel, M.H.E., Waugh, D.A., Feldmann, R.M., and Parsons-Hubbard, K.M., 2008, Experimental

taphonomy of Callinectes sapidus and cuticular controls on preservation: Palaios, v. 23,

p. 615–623.

Nolan, P.R., 2014, A reappraisal of flora in the Bertie Group and their potential significance in

analyzing the environment of late Silurian New York State and Canada, Geological

Society of America, Northeastern Section, 49th Annual Meeting, Lancaster, PA

O'Connell, M., 1916, The habitat of the Eurypterida: Bulletin of the Buffalo Society of Natural

Scienes, v. 11, p. 1–227.

Parsons-Hubbard, K.M., Parsons-Hubbard, K.M., Powell, E.N., Raymond, A., and Walker, S.E.,

2008, The taphonomic signature of a brine seep and the potential for Burgess Shale style

preservation: Journal of shellfish research, v. 27, p. 227-239, doi: 10.2983/0730-

8000(2008)27[227:ttsoab]2.0.co;2.

103

Plax, D.P., and Barbikov, D.V., 2009, Eurypterid (Chelicerata, Eurypterida) findings in

Famennian saliniferous deposits of the Devonian of Belarus: Lithosphere, v. 1, p. 29–38.

Plotnick, R.E., 1999, Habitat of Llandoverian–Lochkovian eurypterids, in Boucot, A.J., and

Lawson, J.D., (eds.), Paleocommunities, A Case Study from the Silurian and Lower

Devonian: Cambridge University Press, Cambridge, p. 106–131.

Rickard, L.V., 1969, Stratigraphy of the upper Silurian Salina Group: New York, Pennsylvania,

Ohio, Ontario: New York State Museum and Science Service. Geological Survery Map

and Chart series no. 12, Albany, NY, 57 p.

Ruedemann, R., 1925, The Bertie Waterlime fauna, in some Silurian (Ontarian) faunas of New

York: New York State Museum Bulletin, v. 265, p. 8–14.

Sarle, C.J., 1903, A new eurypterid fauna from the base of the Salina of western New York: New

York State Museum Bulletin, v. 69, p. 1080–1108.

Scruton, P.C., 1953, Deposition of evaporites: AAPG Bulletin, v. 37, p. 2498–2512.

Selden, P.A., 1984, Autecology of Silurian eurypterids, in Bassett, M.G., and Lawson, J.D.,

(eds.), Autecology of Silurian organisms: Special Papers in Palaeontology, The

Palaeontological Association, p. 39–54.

Shearman, D.J., 1978, Halite in sabkha environments, in Dean, W.E., and Schreiber, B.C., (eds.),

Marine Evaporites: SEPM, Tulsa, Arizona, p. 430–442.

Shuster, C.N., 1982, A pictoral review of the natural history and ecology of the horseshoe crab

Limulus polyphemus with reference to other Limulidae: Physiology and biology of

104

horseshoe crabs. Studies on normal and environmentally stressed animals, v. 81, p. 1–52.

Sloss, L.L., 1969, Evaporite deposition in mixed solutions: AAPG Bulletin, v. 53, p. 776–789.

Smith, N.D., 1970, The braided stream depositional environment: Comparison of the Platte River

with some Silurian clastic rocks, north-central Appalachians: Geological Society of

America Bulletin, v. 81, p. 2993–3014, doi: 10.1130/0016-

7606(1970)81[2993:tbsdec]2.0.co;2.

Smosna, R., Patchen, D., Warshauer, S., and Perry, J., W., 1977, Relationships between

depositional environments, Tonoloway Limestone, and distribution of evaporites in the

Salina Formation, West Virginia, SG 5: Reefs and Evaporites—Concepts and

Depositional Models: American Association of Petroleum Geologists, p. 125–143.

Southgate, P.N., 1982, Cambrian skeletal halite crystals and experimental analogues:

Sedimentology, v. 29, p. 391–407, doi: 10.1111/j.1365-3091.1982.tb01802.x.

Størmer, L., 1976, Arthropods from the Lower Devonian (Lower Emsian) of Alken an der Mosel,

Germany. Part 5: Myriapoda and additional forms, with general remarks on fauna and

problems regarding invasion of land by arthropods: Senckenbergiana Lethaea, v. 57, p.

87–183.

Stumm, E.C., and Kjellesvig-Waering, E.N., 1962, A new eurypterid from the upper Silurian of

southern Michigan: Contributions from the Museum of Paleontololgy, v. 17, p. 195–204.

Tetlie, O.E., 2006, Two new Silurian species of Eurypterus (Chelicerata: Eurypterida) from

Norway and Canada and the phylogeny of the genus: Journal of Systematic

105

Palaeontology, v. 4, p. 397–412, doi: 10.1017/s1477201906001921.

Tetlie, O.E., 2007, Distribution and dispersal history of Eurypterida (Chelicerata):

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 252, p. 557–574, doi:

10.1016/j.palaeo.2007.05.011.

Tetlie, O.E., Brandt, D.S., and Briggs, D.E.G., 2008, Ecdysis in sea scorpions (Chelicerata:

Eurypterida): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 265, p. 182–194,

doi: 10.1016/j.palaeo.2008.05.008.

Tollerton, V.P., Jr., 1997, Eurypterids and associated fauna at Litchfield, a classic locality, in

Rayne, T.W., Bailey, D.G., and Tewksbury, B.J., eds., New York State Geological

Association, 69th Annual Meeting, Clinton, New York, p. 253–264.

Tollerton, V.P., Jr., and Muskatt, H.S., 1984, Sedimentary structures and paleoenvironmental

analysis of the Bertie Formation (upper Silurian, Cayugan Series) of central New York

State, in Brett, C.E., and Scatterday, J., eds., New York State Geological Association,

56th Annual Meeting, Clinton, NY, p. 117–155.

Tourek, T.J., 1970, The depositional environments and sediment accumulation models for the

upper Silurian Wills Creek shale and Tonoloway limestone, central Appalachians:

Unpublished Ph.D. thesis, Unpublished Ph.D. dissertation. Johns Hopkins University,

Baltimore, Maryland, 564 p.

Van der Voo, R., 1988, Paleozoic paleogeography of North America, Gondwana, and intervening

displaced terranes: comparisons of paleomagnetism with paleoclimatology and

biogeographical patterns: Geological Society of America Bulletin, v. 100, p. 11–324.

106

Vannier, J., Wang, S.Q., and Coen, M., 2001, Leperditicopid arthropods (Ordovician–Late

Devonian): functional morphology and ecological range: Journal of Paleontology, v. 75,

p. 75–95.

Viira, V., and Einasto, R., 2003, Wenlock-Ludlow boundary beds and conodonts of Saaremaa

Island, Estonia: Proceedings of the Estonian Academy of Sciences. Geology, v. 52, p.

213–238.

Vrazo, M.B., and Braddy, S.J., 2011, Testing the ‘mass-moult-mate’ hypothesis of eurypterid

palaeoecology: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 311, p. 63–73,

doi: 10.1016/j.palaeo.2011.07.031.

Vrazo, M.B., Ciurca, S.J., Jr., and Brett, C.E., 2014a, Taphonomic and ecological controls on

eurypterid Lagerstätten: A model for preservation in the mid-Paleozoic: Geological

Society of America Abstracts with Programs, v. 46, p. 578.

Vrazo, M.B., Trop, J.M., and Brett, C.E., 2014b, A new eurypterid Lagerstätte from the upper

Silurian of Pennsylvania: Palaios, v. 29, p. 431–448, doi: 10.2110/palo.2014.003.

Warren, J.K., 2006, Evaporites: Sediments, Resources and Hydrocarbons: Springer Berlin,

Heidelberg.

Warshauer, S.M., and Smosna, R., 1977, Paleoecologic controls of the ostracode communities in

the Tonoloway Limestone (Silurian; Pridoli) of the central Appalachians, in Loffler, H.,

and Danielopol, D., (eds.), Aspects of Ecology and Zoogeography of Recent and Fossil

Ostracoda: W. Junk, The Hague, p. 475–485.

107

Waterston, C.D., 1979, Problems of functional morphology and classification in stylonuroid

eurypterids (Chelicerata, Merostomata), with observations on the Scottish Silurian

Stylonuroidea: Transactions of the Royal Society of Edinburgh. Earth Sciences, v. 70, p.

251–322.

Young, G.A., Rudkin, D.M., Dobrzanski, E.P., Robson, S.P., and Nowlan, G.S., 2007,

Exceptionally preserved Late Ordovician biotas from Manitoba, Canada: Geology, v. 35,

p. 883–886, doi: 10.1130/g23947a.1.

108

FIGURES

FIGURE 1. Regional map of North American Appalachian basin and study area. Silurian bedrock exposures are represented by the shaded area; key localities are starred. Herkimer and

109

Ft. Erie mark the approximate bounds of the field area for the northern Appalachian basin; Bass and Winfield indicate the approximate extent of the field area in the central–southern

Appalachian basin. Modified from Vrazo et al. 2014b.

110

FIGURE 2. Evaporitic structures from the Fiddlers Green Formation of New York and Ontario.

111

Scale bars = 1 cm; scales in cm. A) Salt hopper pseudomorphs from the Phelps Waterlime

Member, Neid Rd. Quarry, New York. B) Converse (top) side of A; red evaporitic dendrites visible. C) Isolated salt hopper pseudomorph from the Phelps Waterlime Member, Neid Rd.

Quarry, New York. D) Isolated salt hopper pseudomorph from the Ellicott Creek Breccia,

Ridgemount Quarry, Ontario (YPM #215039). E) Isolated salt hopper pseudomorph from the

Ellicott Creek Breccia, Ridgemount Quarry, Ontario (YPM #212443).

112

FIGURE 3. Examples of evaporitic structures crosscutting biogenic structures in the Bertie

Group. Scale bars = 1 cm; scales in cm. Arrows indicate salt hoppers. A) Eurypterid (Eurypterus) 113

with disruptive salt hopper pseudomorph in pre-, Moran Corner Waterlime Member

(post-Akron Formation, Bertie Group), Moran Corner, New York. B) Nautiloid and putative salt hopper pseudomorphs, unnamed bed beneath Williamsville-Akron Formation boundary, Farmington, New York. Inset: cephalopod with disruptive salt hopper pseudomorph, and eurypterid (Eurypterus?) telson, A Member, Williamsville Formation, Ridgemount Quarry,

Ontario. C) Thrombolite with disruptive halite evaporite, Ft. Hill Waterlime Member (Oatka

Formation), near LeRoy, New York. Modified from Ciurca, 2013. D) Black organic material

(microbial?) with salt hopper pseudomorph, A Member, Williamsville Formation, Ridgemount

Quarry, Ontario. Modified from Ciurca, 2013.

114

FIGURE 4. Eurypterus sp. carapaces with disruptive evaporites from the Ellicott Creek Breccia

(Fiddler’s Green Formation), Ridgemount Quarry, Ontario. Scale bars = 1 cm. A) YPM# 214965, 115

with large salt hopper pseudomorph in center and disrupted margins. B) YPM# 217552, with disruptive salt hoppers pseudomorphs near right eye, along margins, and in carapace center. C)

YPM# 217513, with early-stage salt hopper/halite pseudomorph in carapace center. D) YPM#

212262, with multiple early-stage salt hopper/halite pseudomorph structures. E) YPM# 214955, with salt hopper pseudomorph in center of carapace and highly disrupted margin on the right side of carapace. F) YPM# 217657, with isolated salt hopper pseudomorph in center of carapace.

116

117

FIGURE 5. Cartoon model of generalized depositional environment succession leading to salt hopper development in eurypterid-bearing units in the Appalachian basin. Not to scale. A)

Subtidal environment, following transgression. Eurypterids and limited marine fauna are present, as are stromatolites/thrombolites. B) Generalized intertidal–supratidal environment, following regression. Evaporation (wavy arrows) begins to produce desiccation cracks. Eurypterids are absent and remains are buried. Only tolerant euryhaline organisms (e.g., leperditicopids) are present as conditions become increasingly hypersaline and/or dysoxic. C) Supratidal–sabkha-like environment. Continuing regression and evaporation results in hypersaline conditions and units are barren. Supersaturation of groundwater with NaCl leads to in situ salt hopper formation in the sub-surface. Eurypterids and microbial material appear to act as nucleation points (see Fig. 3).

118

Chapter IV

Paleoecological and Stratigraphic Controls on Eurypterid Lagerstätten: A Model for Preservation

in the Mid-Paleozoic

Matthew B. Vrazo1*, Carlton E. Brett1, and Samuel J. Ciurca, Jr2

1Department of Geology, 500 Geology/Physics Building, University of Cincinnati, Cincinnati,

Ohio 45221-0013 USA

22457 Culver Road, Rochester, NY, 14609, USA

Keywords: Appalachian basin, Silurian–Lower Devonian, sequence stratigraphy, thrombolite/, soft-tissue

119

ABSTRACT

We examine the likelihood that formation of eurypterid Lagerstätten in the mid-Paleozoic of

Laurentia is controlled by changes in water depth, within a sequence stratigraphic framework.

We carried out a taxonomic and environmental survey on all eurypterid-bearing intervals in the

Silurian–Lower Devonian of the Appalachian basin, which has yielded the most prolific assemblages of these arthropod fossils in the world. Canonical correspondence analysis (CCA) indicates a strong lithological gradient between groupings of eurypterid taxa throughout the basin. CCA results, in conjunction with other quantitative analysis and field observation, indicate that a number of eurypterid genera in the basin frequently occur above microbial structures

(thrombolites, stromatolites) and beneath indicators of increased salinity or sub-aerial exposure

(evaporitic minerals, desiccation cracks), and that associated faunal diversity is greatest within eurypterid-bearing units. Based on these parameters, we present a sequence stratigraphic model in which microbial structures represent flooding surfaces and evaporites/sub-aerial exposure features represent the tops of shallowing-upward parasequences. In this scenario, eurypterids primarily occur within freshening conditions concomitant with minor transgressions; subsequent shallowing-up successions promote hypersalinity and anoxia, which facilitate soft-tissue preservation. In the central and southern region of the basin where microbial structures and evidence for hypersalinity are less common, a similar pattern of cyclical shallowing-upward deposition within eurypterid-bearing units holds. Thus, eurypterid preservation appears to reflect a combination of ecological preferences and abiotic conditions that promote inhabitation and eventual preservation within the same setting, and ultimately suggests that eurypterid

Lagerstätten in the mid-Paleozoic are controlled primarily by water depth.

120

INTRODUCTION

The distribution of organismal occurrences in the geologic rock record can be predicted using the cyclical control of sea level fluctuations on water depth (Brett 1998; Patzkowsky and

Holland 2012). Within this revised, holistic view of preservation, increased attention is being given to the control of sea level on the formation of soft-tissue Konservat-Lagerstätten, rare preservational occurrences which were traditionally thought to be byproducts of unique, chance events. Seilacher et al. (1985) first suggested that Lagerstätten were end-members of otherwise normal sedimentary processes, and thus the specific suite of environmental and preservational conditions that lead to their formation should allow them to be “prospected” in the rock record.

Following the sequence stratigraphic model of Van Wagoner et al. (1990) and others, Brett

(1995) and Brett et al. (1997) demonstrated that consideration of Lagerstätten within a sequence stratigraphic framework can inform both the likelihood of exceptional preservation of certain faunas, and their predictability in adjacent facies. Subsequent field studies have begun to highlight the sequence stratigraphic control over soft-tissue preservation, primarily in early

Paleozoic Lagerstätten in the Cambrian (Webster et al. 2008; Brett et al. 2009). These initial studies suggest that a predictive approach through a sequence stratigraphic lens can be applied to understanding the formation and paleoecological implications of younger Lagerstätten, such as those containing well-preserved eurypterid faunas in the Silurian–Early Devonian (Clarke and

Ruedemann 1912; Ciurca 1978; Kluessendorf 1994).

Eurypterids were a diverse and geographically widespread order of aquatic chelicerate arthropods that existed from the Mid-Ordovician until the end-Permian (Tetlie 2007; Dunlop

2010). Although this clade was more species-rich than all other Paleozoic chelicerates combined, eurypterids generally have a poor fossil record. This is largely due to a chitinous, non-

121 biomineralized exoskeleton that was prone to degradation under normal marine conditions

(Poulicek and Jeuniaux 1991; Cody et al. 2011). In considering this physiological bias against preservation in normal marine settings, Brooks (1957), and later, Plotnick (1999), posited that conditions that are ideal for eurypterid preservation, e.g., marginal or hypersaline settings, may not always reflect those of inhabitation. This apparent taphonomic bias has limited our understanding not only of basic aspects of eurypterid ecology, such as habitat preference and salinity tolerance, but also temporal trends in eurypterid evolution, for example, the drivers behind the eurypterid marine-to-freshwater transition that began in the early Silurian and ended by the Late Devonian (Plotnick 1999; Lamsdell and Braddy 2010).

Punctuating the poor quality and patchy eurypterid fossil record, however, are eurypterid

Lagerstätten, in which numerous individuals are preserved in remarkable detail. Such sites are known from the mid-Ordovician (Lamsdell et al. 2015) onward across multiple paleocontinents, but perhaps the most prolific are those found in nearshore carbonate ramp settings in the Silurian of Laurentia and Baltica (Clarke and Ruedemann 1912; Kaljo 1970; Kluessendorf 1994).

Regular preservation in these marginal, often hypersaline marine environments, particularly those in the Laurentian Appalachian basin, has been attributed to various factors including an ecological preference for restricted settings in which certain groups may have molted or mated en masse (Braddy 2001; Vrazo and Braddy 2011), environmental conditions conducive to preservation (e.g., anoxia, hypersalinity; Kluessendorf 1994; Chapter III), and a paucity of biostratinomic activity concomitant with restricted or marginal environments (e.g., bioturbation, ). However, bed-level interpretation of depositional environment, and ultimately, habitat, in these Lagerstätten deposits has traditionally been compromised by a frequent lack of sedimentary evidence for depositional environment, and coarse lumping of contemporaneous

122 fauna and adjacent stratigraphy (Clarke and Ruedemann 1912; Alling and Briggs 1961; Leutze

1961; Selden 1984; Feldman et al. 1993; Plotnick 1999; Chapter II).

A growing body of evidence now suggests that accurate interpretations of eurypterid habitats and faunal associations within these depositionally ambiguous units can only be made through a high-resolution bed-level approach (Ciurca 1973; Maples and Schultze 1988; Plotnick

1999; Tetlie and Poschmann 2008; Chapter II; Chapter III). Ciurca (1973; 1978), Hamell and

Ciurca (1986), Ciurca, (1990), and Ciurca and Hamell (1994) first documented cyclical occurrences of eurypterid-rich dolomitic “waterlimes” in northern Appalachian basin Silurian localities. More recently, Vrazo et al. in Chapter II revealed a strong stratigraphic and environmental control on eurypterid occurrences in the central basin. Eurypterids in the uppermost Silurian of Pennsylvania only occur within the initial deepening and freshening portion of a transgressive sequence, despite the prevalence of presumably ideal preservational conditions in adjacent hypersaline facies. In Chapter III, it was demonstrated that evaporite- eurypterid associations in the Appalachian basin, which were traditionally taken as evidence for deposition in hypersaline environments, were actually the result of early-stage diagenetic overprinting, and should not be used as indicators of conditions at the time of burial. Chapter III also demonstrated that the conditions that are conducive to both inhabitation (i.e., near euhaline conditions) and preservation (i.e., hypersalinity/anoxia) can occur within the same marginal setting.

Taken together, these investigations indicate that inhabitation and eventual preservation of eurypterids may be dictated by a single overarching control, such as water depth. In the present study, we test this hypothesis by performing a survey and quantitative analysis of all eurypterid-bearing localities in the mid-Paleozoic (Silurian–Early Devonian) of the Appalachian

123 basin, within a sequence stratigraphic framework. We overcome previous stratigraphic challenges within studies of eurypterid habitats by focusing on bed-level occurrences. The results of these analyses indicate that eurypterids preferentially occupied freshening conditions recorded during small-scale transgressions, and from this, we propose a model for the formation of eurypterid Lagerstätten in nearshore settings. In this model, regional-scale sea level fluctuations create widespread environmental conditions that are both conducive to eurypterid inhabitation, and to the preservation of soft-tissue cuticle. We conclude that eurypterid Lagerstätten in nearshore settings are the result of both ecological and environmental influences and that their appearance can ultimately be predicted within a sequence stratigraphic framework.

GEOLOGICAL SETTING

This study focuses on the eurypterid-bearing Silurian–Lower Devonian units deposited on the eastern and northern margins of the Appalachian foreland basin of Laurentia. The

Appalachian basin is a northeast-southwest trending trough that extends approximately 300 km from central New York to central West Virginia, and was developed initially owing to tectonic loading during the during the Taconic Orogeny in the Late Ordovician (Brett et al. 1990). Terrigenous siliciclastic and marine-derived carbonate facies occur on the shallow basin margins in the lower Silurian; in upper Silurian–Lower Devonian units, limestones and argillaceous dolostone deposition dominate the northern and eastern nearshore, while thick evaporite deposits occur in the basin depocenter (Alling and Briggs 1961; Rickard 1969). The evaporitic nature of the basin at this time most likely reflects a low paleolatitude, arid climate, and partial restriction from input (Dennison and Head 1975; Van der Voo 1988).

124

Eurypterids first appeared in the basin in the Late Ordovician, where they were found within siliciclastic facies in open marine environments (Caster and Kjellesvig-Waering 1964;

Tollerton 2004). In the latest Ordovician–earliest Silurian Whirlpool Formation of western New

York/southwestern Ontario (Schröer et al. 2016) eurypterids begin to appear in more nearshore settings with variable salinities (Tetreault et al. 1994). From that time, until the Middle

Devonian, eurypterids are found locally in most major intervals in the Appalachian basin, but almost never in open marine, offshore facies (Plotnick 1999).

METHODS

To assess regional-scale stratigraphic controls on eurypterid deposits, we compiled data on all known Silurian–Early Devonian-age eurypterid-bearing localities in the Appalachian basin

(i.e., eastern Ohio/southwestern Ontario to easternmost-central New York; northern New York to southwestern West Virginia and western Maryland) (Fig. 1). Our survey approach builds on that of Plotnick (1983, 1999), who compiled the largest literature-based global eurypterid occurrence dataset to date. In the present study, eurypterid occurrences were exhaustively collated primarily from extensive field observations made by one of us (SJC), accession data from the Yale

Peabody Museum Ciurca Collection, observations made by us during field studies in 2013–2015, and the primary literature, where necessary. We then restricted our survey to localities and strata where eurypterid occurrences could be identified to the submember-level, and preferably, horizon-level, and adjacent units. This yielded a data set comprising 32 formations, 69 members, and 78 sub-members, across 88 localities. From these we obtained 241 bed or horizon-level samples, of which 111 contain eurypterids (Supplemental Table 1). Eurypterid and associated faunal taxonomic occurrence data were compiled primarily at the genus-level, but higher

125 taxonomic levels were used for common, but generically unidentified taxa (e.g., “high-spired gastropods”). This yielded 19 eurypterid genera and 45 distinct associated taxonomic assignments, roughly a third of which are brachiopods. Within the survey dataset, only four formations—the Camillus, Forge Hollow, Oatka, and Akron formations—lack eurypterids, but these were retained because they are lithologically and environmentally similar to adjacent eurypterid-bearing units. For each sample, sedimentological variables recorded included primary and secondary lithologies, and presence of sedimentary features (e.g., ripple marks, desiccation cracks, brecciation), evaporitic structures or minerals, biogenic structures such as stromatolites and thrombolites, and bioturbation. Sedimentary structures such as cross-bedding are typically observed only at the micro-scale in many upper Silurian units (Ciurca and Hamell 1994) and thus were excluded from the survey.

We then placed all samples within a sequence stratigraphic framework with objectively defined flooding surfaces and cycle boundary horizons. Features such as desiccation cracks and collapse breccias, indicative of subaerial exposure surfaces, record intervals of maximum regression. Abrupt contacts between such surfaces and overlying facies, commonly with lags of intraclasts, oncoids, marine fossils, bioturbation, and/or mounded microbial structures, were used to demarcate cycle (parasequence) boundaries or flooding surfaces at the bases of thin, small-scale transgressive deposits (TSTs). Upward appearance of shallower water facies, including wavy laminated microbialites, vugs, evaporite molds, and desiccation cracks, was used as evidence for regression in small scale highstand systems tracts (HSTs) (cf. Handford and

Loucks 1993).

To quantify the likelihood of eurypterids occurring within specific lithologies (e.g., carbonates or siliciclastics) as an indicator of overall environmental preference (or preservational

126 bias), we used the binomial substrate affinity analysis of Kiessling and Aberhan (2007), which follows that of Foote (2006). Both analyses require the number of occurrences associated with one target lithology or type of sedimentary structure, the number of occurrences in alternative lithologies or non-occurrences with sedimentary structures, and the total number of global occurrences of either lithology or structure. The analysis outputs a probability of affinity and a p- value indicating significance level. Additionally, we also tested for an “affinity” toward evaporites and microbial structures following Vrazo et al. (Chapter III), who noted a frequent co- occurrence of eurypterids and these sedimentary structures. Such features may be useful as an indication of water depth and minor sea level fluctuations in settings that otherwise lack sedimentary features.

To assess regional-scale taxonomic and environmental relationships, canonical correspondence analyses (CCA) were carried out in the Vegan package (Oksanen et al. 2015) in the R programming language (R Core Team 2015). For all multivariate analyses, samples lacking faunal occurrence data and singleton taxa were removed a priori. An initial exploratory horizon/site-level analysis revealed that the eurypterid genus Waeringopterus, which primarily occurs as an isolated taxon in the lowermost Syracuse Formation, represents an extreme outlier.

Waeringopterus was thus removed from the subsequent horizon-level analysis. The significance of individual environmental variables within the CCA was determined using a test similar to an

ANOVA, in which community data is permutated to a high number (9999; Oksanen et al. 2015).

Significant environmental variables (at the α = 0.05 level, or lower) were then retained for CCA plots.

Some localities and intervals in the survey have been heavily sampled (e.g., the Phelps

Waterlime Member at Passage Gulf, NY), whereas most are relatively depauperate, with many

127 containing only one or two taxa. To reduce the potential influence of over-sampled localities in analyses, the dataset was also aggregated into groupings of sub-member level samples (or higher, depending on the stratigraphic subdivisions per unit). Faunal sample occurrences were also aggregated, but counts were retained only as presence/absence data in subsequent CCAs. This aggregation has the effect of removing locality-level bias from the dataset, while potentially increasing the faunal diversity at the smallest possible subdivision. Additionally, a subset of the data restricted to New York and Ontario localities was tested for a potential gradient along the east-west outcrop belt strike as it relates to shifts in the basin depocenter over time (Brett et al.

1990).

RESULTS

Eurypterids occur in all Silurian–Early Devonian groups in the survey. A vast majority of eurypterid occurrences (n = 96) are in the northern Appalachian basin (New York and Ontario).

Eurypterids occur primarily in cyclic carbonate-dominated or mixed carbonate-mudstone lithologies in the Silurian–Lower Devonian of the Appalachian basin (81%; 90:111 samples).

The remaining 21 eurypterid-bearing samples occur in shales and siltstones. For eurypterid affinity toward carbonates or siliciclastic substrates, we obtained a high but non-significant probability value of 0.81 (p = 0.92) for the target carbonate lithology, indicating that there is not a strong substrate bias across the basin. If the sample is reduced only to the northern basin, the probability value and p-value remain similar.

Among all sedimentological and biogenic features recorded, the co-occurrence of eurypterids and evaporitic structures was the most frequent. Of 59 samples containing evaporites

(i.e., salt hoppers), 53% (n = 31) of these also contained eurypterids on the same horizon. This

128 association is restricted to localities in the northern basin (Ontario and New York). Within a given bed (or series of beds) eurypterids are typically subjacent to, or co-occur with these structures; they are rarely found above them. Vrazo et al. (Chapter III) observed a largely similar pattern in a survey of eurypterids and evaporites in the basin (see Chapter III for further discussion). Other evaporitic features (i.e., desiccation cracks) occur in 22 samples, all within upper Silurian units. Desiccation cracks typically occur at the tops of intervals on which eurypterids occur and there are no co-occurrences of these features and eurypterids in the same horizon.

This frequent eurypterid-evaporite association is followed closely by a co-occurrence with microbial structures (thrombolites, stromatolites, microbial mats); of 65 samples that contain microbial structures, eurypterids occur directly within sediments emplaced upon stromatolites, thrombolites, or microbial mats in just under half (42%; n = 27). Conversely, of

111 eurypterid occurrences, 36 (32%) of them are associated with microbial structures. These associations are restricted to New York, Ontario, and Pennsylvania. If the samples are reduced to only those in New York and Ontario, where these structures predominantly occur, they are found in 35% (34:96) of all samples. Ciurca and Domagala (1988), Ciurca (2005; 2013), and Vrazo et al. (Chapter III) have previously noted a close association between eurypterids and microbial structures across the upper Silurian of the northern Appalachian basin (Fig. 2).

Having ascertained that microbial structures and evaporitic structures are the most common sedimentary features within eurypterid-bearing samples within the northern

Appalachian basin, we then carried out a post hoc analysis on a subset of the dataset restricted to samples from that region. For evaporite-eurypterid associations, the significant affinity probability value was similar to our raw co-occurrence value (36%; p < 0.05). A similar

129 significant affinity probability was obtained from the analysis of the microbial structure- eurypterid associations (40%; p < 0.05). In terms of taxonomic associations, 12 of the 19 (63%) eurypterid genera recorded in the survey occur with or directly above microbial structures in at least one sample. Of these taxa, Eurypterus occurs with these structures the most frequently (in

26:66; 40% of Eurypterus-containing samples). A smaller subset of these same taxa also occur with, or beneath halite evaporite structures (6:19; 32%), with Eurypterus again the most common genus to occur with these structures (in 38% of Eurypterus-containing samples). The recurrent microbial/evaporite-eurypterid associations occur in both carbonate and siliciclastic facies, and are observed in three of the four end-member cycles described below.

The general co-occurrences of eurypterids and other fauna at the sub-member level are presented in Table 1. Leperditia is the single most common taxon to occur with eurypterids, followed by the inarticulate Lingula (n = 14). Non-lingulate brachiopods

(rhynchonellids, strophomenids) comprise the single largest overall combined faunal group in term of total occurrences, followed by nautiloid cephalopods. Associated faunal diversity results obtained during our survey are generally similar to those of Plotnick (1999, table 10.3) in terms of overall taxonomic composition, although our results are restricted to occurrence data at the horizon level for the Appalachian basin in the Silurian–Lower Devonian. To determine if there was a difference in relative faunal diversity between eurypterid-bearing and non-eurypterid- bearing beds, we compared the total diversity within eurypterid-bearing samples to that of non- eurypterid-bearing samples with a taxon count of at least one (n = 55; n = 47, respectively).

Mean faunal diversity is significantly greater in eurypterid-bearing beds (Mann-Whitney, p <

0.01).

130

A CCA of all taxa, sampled at the horizon level, with only significant (p < 0.05) environmental variables retained (Fig. 3) reveals a strong lithological gradient, with siliciclastics

(shale/siltstone) on one end, and carbonates (dolostone/limestone/mottled limestones) at the other end (Fig. 3). Representative stratigraphic units in the upper left quadrant of the plot (Fig 3, inset), e.g., the Tuscarora or Rose Hill formations, are entirely siliciclastic-dominated, whereas representative units in the center and lower right quadrant of the axis, with positive scores on

CCA 1, e.g., the Cobleskill Formation, are chiefly carbonate-dominated. Most eurypterid taxa occur near the center of the plot, or along the siliciclastic vector of the lithology gradient.

Associated faunal composition does not appear to be as tightly constrained by the significant environmental variables as that of eurypterids. Running orthogonally to the main lithological gradient is another unconstrained axis along which several eurypterid taxa (i.e., Erieopterus

[Lower Devonian Manlius Formation], Eusarcus [upper Silurian Eramosa Formation], and

Carcinosoma [various upper Silurian formations]) and rare stenohaline taxa (e.g., rare and trilobites) occur. However, most associated fauna cluster in the center of the lithological gradient, or slightly toward the right along the dolomite variable. The rare brachiopod

Whitfieldella, which is found in only three samples and occurs primarily in the Victor Formation, represents the furthest outlier among the associated fauna.

A CCA of all taxa, following aggregation of taxa to the sub-member level (or next highest stratigraphic level), with only significant (p < 0.05) environmental variables retained

(Fig. 4), reveals a very similar lithological constraint on faunal associations as at the horizon- level (see Table 2 for all environmental variables). Additionally, in the lower right quadrant of the CCA plot, “Halite” now exerts a significant influence on faunal associations, in a similar direction to the “Dolomite” vector. Two other variables, “Thrombolites” and “Ripple Marks”,

131 also now exert a significant influence, although to lesser extent. The “Thrombolite” variable aligns with the “Dolomite” and “Halite” vectors. The “Ripple Marks” vector aligns with the

“Halite” vector. Ripple marks are generally uncommon in organism-bearing samples at the horizon-level; however, aggregation has increased their influence (and significance) within the

CCA. Following stratigraphic aggregation, most non-eurypterid taxa remain clustered toward the center of the axes, or toward the negative side of CCA axis 1, along the siliciclastic vectors, with the exception of Erieopterus, which now forms a strong outlier along CCA 2.

A CCA of only eurypterid taxa following aggregation to the sub-member level (or next highest stratigraphic level), with only significant (p < 0.05) environmental variables retained

(Fig. 5), yields similar results to those in earlier CCAs, but with increased division based primarily on lithology (siliciclastic versus dolostone). Nearly all representative stratigraphic units in the negative portion of the CCA 2 axis are siliciclastic dominated, whereas those in the upper, positive portion. As in Figure 4, halite exerts the strongest influence after lithology based on vector length. Additionally, microbial structures (the “Thrombolite” and “

Microbial Mat” variables) now exert a similar influence. As in the CCA of all fauna (above),

Erieopterus continues to form a strong outlier. An additional CCA on only New York- and

Ontario-based samples (unfigured) indicates there is no significant east-west influence on the overall composition of the fauna (p = 0.181).

Depositional Cycles

Within eurypterid-bearing lithofacies, several distinct but interrelated types of meter- scale cycles, with specific sedimentological and faunal features, were observed in the field across the basin. These are described briefly below and depicted in Figure 5.

132

Bertie-Manlius-type cycles.—Meter-scale cycles are observed in the late Silurian (Přídolí) Bertie

Group and overlying Early Devonian (Lochkovian) Manlius Formation. These facies are characterized by meter-scale cycles that typically commence with thin basal intraclastic packstone lag deposits that may be capped by low relief (2–10 cm relief) microbial buildups composed of stromatolites and/or thrombolites. These are overlain by lime mudstones,

"waterlimes" or calcareous shales, which occasionally contain bioturbation and may contain low- diversity faunas of ostracods, leperditians, small gastropods, nautiloid cephalopods, and lingulate and rhynchonelliform brachiopods, and in some cases, abundant, well-preserved, eurypterids.

Mineralized fossils show substantial dissolution and are represented by deformed internal/external molds, but organic skeletons, including eurypterid may be well preserved. Dolostones with evaporitic features including salt hoppers, incipient halite casts/molds, gypsum molds, and collapse breccias suggestive of surface evaporation/solution, are typical of upper portions of cycles (cf. Chapter III). In the Bertie Group alone, 43% (26:60) of samples in the present study show such evaporitic evidence in successions overlying eurypterid- bearing strata.

Vernon (“Pittsford Shale”)-Bloomsburg-type Cycles.—An analogous type of cycle is present in more siliciclastic rich successions in the Ludlow-age upper Bloomsburg (PA), McKenzie (PA),

Illion (NY), and Vernon (NY) formations. These show basal thin carbonates with thin lags and typically low microbial mounds (stromatolites) that pass upward into medium to dark gray shale with varied fossils including lingulates, bivalves, gastropods, ostracods and, in some cases, eurypterids. These dark shales pass upward into blue to green to reddish mottled mudstones that

133 contain evidence for sub-aerial exposure including evaporites (salt hoppers), paleosols, and/or desiccation features.

Tonoloway-type cycles.—Cyclicity in the upper Silurian (upper Ludlow–Přídolí) Tonoloway

Formation of Pennsylvania, West Virginia, and Maryland has been well-documented elsewhere

(Cotter and Inners 1986; Elick and Siegel 2009). The successions in this unit are comparable to those of the “Vernon-Bloomsburg” described above, but within a more carbonate-dominated lithofacies. Thick micrite beds containing isolated thrombolitic mounds or microbial laminae occur at the base of meter-scale shallowing-up successions. These are overlain by thin-medium- bedded calcareous shales containing a very low diversity fauna, which typically consists only of mass assemblages of leperditicopids, but, rarely, contains a more diverse near-stenohaline marine fauna that includes molluscs, favositid corals, and abundant eurypterids (e.g., Chapter II). These beds are then overlain by thin-bedded and barren calcareous shales that frequently contain evidence for sub-aerial exposure including desiccation cracks, halite casts/molds, and vugs.

Wills Creek Type Cycles.—Cycles in the Ludlow-age Wills Creek Formation of the central and southern Appalachian basin are comparable to those of siliciclastic-dominated units to the north, but generally lacks the microbial component. Thin carbonate beds grade into olive-grey shales or red siltstones that may contain a limited fauna comprising lingulate brachiopods, ostracods, and rare fish and eurypterid remains (e.g., Kjellesvig-Waering and Leutze 1966; MBV, personal observations). These beds are capped by small-scale desiccation features and ripple marks.

Evaporitic structures such as vugs and halite casts occur within the Wills Creek Formation,

134 though these have not been observed in association with eurypterids. This interval represents the southernmost known occurrence of eurypterids within the Appalachian basin.

Tuscarora/Shawangunk-type Cycles.—The early Silurian (Llandovery) Tuscarora and

Shawangunk Formations contain entirely siliciclastic facies and bed thickness typically varies rapidly across strike. Cycles in these comprise alternating massive, heavily cross-bedded white quartz arenite and thinner coarse-grained black or gray siltstone or mudstone beds. Arthrophycus occurs in both units, but the arenite beds are otherwise depauperate, whereas occasional Lingula and pyritized burrows occur in the silts/muds, as well as fragmentary remains from a diverse eurypterid fauna (e.g., Swartz and Swartz 1931; MBV, personal observations).

DISCUSSION

The substrate affinity analysis indicates that, as a whole, eurypterid occurrences in the

Appalachian basin are not biased toward occurrence (or preservation) in a single lithology (i.e., carbonates). The results of the horizon-level and aggregated CCAs support this, with most eurypterid taxa either falling toward the center of the plots, or along the shale/siltstone vectors.

However, when considering only eurypterid taxa, there does appear to be a strong influence of lithology on the occurrences of individual genera and their associations with other eurypterid taxa (Fig. 5). Although we did not test for the likelihood of co-occurrence in more than one lithology, the results of the eurypterid-only CCA indicate that most eurypterid taxa are more likely to occur in only one lithofacies. One exception is Eurypterus, the most common genus considered in this study. Eurypterus falls toward the center of most plots, suggesting that it was a eurytopic and widespread taxon. Eurypterids do not typically appear in reefal deposits where

135 corals and stromatoporoids are more common (e.g., in the upper right quadrant of Fig. 3), with the exception of Erieopterus, which is thought to replace Eurypterus in Lower Devonian deposits and is found in biohermal deposits (Ciurca 1978). This may explain its isolation in Figures 3–5.

Associated faunal composition does not appear to be as tightly constrained by the significant environmental variables as that of eurypterids, and this most likely influenced the position of eurypterid taxa within Figures 3 and 4. Extremely common associated fauna such as

Leperditia and Lingula are similar to Eurypterus in that they occur closest to the center of the lithological gradient, and this supports the traditional view that these are euryhaline, eurytopic taxa. Notable, however, is the occurrence of Lingula away from the “Halite” vector in Figure 4.

In Chapter III, it was noted that Lingula has not been found in any unequivocally hypersaline depositional settings, and the results of the CCA here seem to support a preference for eu- or hyposaline settings. Conversely, only a few close associations of eurypterids and single non- lingulate brachiopod genera occur away from the main lithological gradient, i.e., Eusarcus and

Orbiculoidea, and Erieopterus and Howella. Both taxonomic pairings fall along the gradient that is orthogonal to the main lithological gradient (Fig. 3). Post hoc review of additional associated fauna, which includes cephalopods and other typically stenohaline taxa, suggests that these pairings (along an unconstrained gradient) may reflect euhaline conditions. In considering

Whitfieldella as a distant outlier in Figure 3, Tollerton (1997) noted that Protathyris is often misidentified as Whitfieldella. Given that Protathyris is very common in the Victor Formation, it may be that the few examples of Whitfieldella actually represent the former genus, in which case they would lie closer to the center of the plot.

136

Sedimentary Associations

After lithological affinities, eurypterids in the Appalachian basin appear to have the strongest association with evaporitic and microbial structures, particularly in the northern basin.

The close association of eurypterids with or above microbial structures in this region is supported by the substrate affinity analysis, CCA results, and qualitative observations. These structures and associated eurypterids typically occur at the bases of shallowing-up successions (Fig. 6), which we interpret here as parasequence boundary markers and the flooding surfaces associated with small-scale transgressions. In this scenario, the regular occurrence of eurypterids on or directly above these flooding surfaces suggests that eurypterids preferentially entered these nearshore environments during minor transgressive events that brought freshening conditions into nearshore subtidal settings. The occasional return to near-euhaline marine conditions above these microbially dominated beds is supported by an increase in faunal diversity within eurypterid- bearing horizons that includes both classically euryhaline (Leperditia, Lingula) and more stenohaline taxa (non-lingulate brachiopods, bryozoans, cephalopods, corals).

Similarly, substrate affinity analysis, CCA, qualitative observations, and earlier studies

(i.e., Chapter III) indicate that there is a close and regular association of eurypterids with halite evaporites in the northern basin. Given the role of evaporation/regression on the formation of evaporites in shallow nearshore settings in the basin (Chapter III), the occurrence of eurypterids with and above these structures suggestions that their burial and preservation is linked to changes in the environment due to changes in water depth. If freshening conditions during small-scale transgressions were conducive to eurypterid inhabitation, the frequency of desiccation features toward the top of these shallowing-up successions suggests that a subsequent drop in water depth and/or rapid burial played a critical role in their preservation. Where eurypterids and salt hoppers

137 co-occur in the same bed, we interpret this association as a post-burial condition (Chapter III).

The presence of salt hoppers in fossiliferous beds most likely reflects in situ formation within the sediment following minor regressions, i.e., they are the result of early-stage diagenesis under an extended evaporative or regressive regime due to a gentle paleoslope across the basin and a predominantly shallow water depth (Alling and Briggs 1961; Smosna et al. 1977; Belak 1980;

Cotter and Inners 1986; Dorobek and Read 1986; Bell and Smosna 1999). The shift from near- euhaline conditions to hypersaline or briny conditions would create an environment that was uninhabitable for most taxa (including eurypterids) while reducing potential disruption of buried exoskeletons via chitinoclastic bacterial decay. It has been demonstrated that chitinoclastic bacterial degradation of chitinous tissues in the water column is not deterred by anoxic conditions (e.g., Poulicek et al. 1998; Perga 2011), but is strongly inhibited by increased salinity or brines (Seki and Taga 1963; Mutel et al. 2008; Parsons-Hubbard et al. 2008). The frequency of desiccation cracks at the tops of many eurypterid-bearing beds and the lack of any regular fauna (aside from leperditians) in these intervals not only confirms the regular shallowing-up nature of these successions, but also indicates regular surface evaporation, which invariably increased salinity in the water column and vadose zone.

As with extreme hypersalinity, chitin degradation is significantly slowed within the sediment (Schimmelmann et al. 1986; Boyer 1994; Kirchman and White 1999; Perga 2011).

Rapid burial is widely accepted as a requirement for soft-tissue preservation in the fossil record, but there is little macro-sedimentological evidence for episodic burial in the shallow peritidal nearshore settings of the Appalachian basin. Instead, microbial structures in the subtidal and lowermost intertidal zone may have facilitated soft-tissue preservation through physical baffling of sediments. LoDuca and Brett (1997) suggested that the Medusaegraptus Lagerstätte in the

138

Niagara Falls Member of the upper Silurian Goat Island Formation was primarily the result of anoxic conditions that may have developed in between relict biostromes during eustatic transgression. A similar pattern, where minor transgressions promoted sedimentation and burial in between small microbial baffles, may have occurred in younger units containing eurypterids.

Moreover, coating of eurypterid skeletons by rapidly growing microbial films could have further aided preservation via bioimmuration (cf. the "death masks" of Gehling 1999). From the above environmental parameters, we propose a generalized preservational model in which eurypterids entered nearshore settings during transgressive freshening conditions, and were subsequently buried prior to development of briny or anoxic conditions conducive to soft-tissue preservation

(Fig. 7).

In siliciclastic-dominated facies that lack obvious evidence for hypersalinity in the central and southern Appalachian basin, sea-level dependent controls on eurypterid preservation are still evident. In the upper Silurian Wills Creek Formation, eurypterids occur within fissile mud shales that are bounded by subjacent limestone units (representing perhaps late TST/early HST) and suprajacent horizons that contain desiccation cracks. Eurypterids in the lower Silurian

Shawangunk Formation of New York (Clarke and Ruedemann 1912) and the coeval Tuscarora

Formation of Pennsylvania (Swartz and Swartz 1930; Swartz and Swartz 1931) only occur in arenaceous silt bands interbedded between massive Arthrophycus-rich quartz-arenite beds. Here, eurypterids appear to occur only within small-scale transgressive beds within a 4th order deepening sequence. Similarly, in the McKenzie Formation of Pennsylvania, eurypterids are only currently known from transitional shales suprajacent to limestone beds, in some cases with microbial structures. In these units, there is no evidence for hypersalinity and few other

139 sedimentological or biological features other than rare brachiopods and occasional horizontal and, in some cases pyritized burrows including Chondrites (MBV, personal observations, 2014).

The common feature that underlies all of these occurrences is not association with hypersaline facies, but changes in water depth. In both carbonate and siliciclastic successions, eurypterids are selectively preserved in transgressive marine-influenced facies interbedded with marginal marine to non-marine facies. The associated faunas of these earlier eurypterid assemblages include a low diversity of mollusks, especially bivalves, lingulate and small rhynchonellid brachiopods, and occasional nautiloids, typically assigned to benthic assemblage

(BA) 1 or 2 (e.g., Plotnick, 1999); i.e., sheltered, low energy nearshore areas above normal wave base. More typical offshore marine faunas such as diverse brachiopods, bryozoans, echinoderms, and trilobites are absent, except in rare cases. Some of these settings may record estuarine environments and may even have been hyposaline, though evidence for the latter is only circumstantial (e.g., Barnes 1989; see Silurian-specific discussion in Chapter III). In either case, a continuous theme among both early and late Silurian occurrences is not the prevalence of hypersaline conditions but rather, a propensity of eurypterids to inhabit nearshore settings, perhaps including bays and estuaries.

Although we did not exhaustively survey sites beyond the Appalachian basin, our model appears to be applicable to similar eurypterid-bearing carbonate facies elsewhere, in both

Silurian and Ordovician units. In the upper Silurian Leopold Formation of Somerset Island in the

Canadian Arctic, for example, Dixon and Jones (1978) and Jones and Kjellesvig-Waering (1985) noted that eurypterids occur in beds overlying stromatolites, in a transgressive interval that is overlain by evaporitic and desiccation-cracked beds. A similar pattern is seen in the shallow carbonate settings in the lower Silurian (Wenlock; ) of Saaremaa Island of Estonia

140

(Kaljo 1970; Viira and Einasto 2003; Meidla et al. 2014). A similar association of eurypterids and salt hoppers and/or microbial structures emerges in Upper Ordovician localities in Canada, such as the Georgia Bay and Stony Mountain formations of Mantoulin Island and Manitoba, respectively (Stott et al. 2005; Young et al. 2007; Young et al. 2012), suggesting similar habitat preferences and/or preservational conditions early in the evolutionary history of eurypterids.

Likewise, preservation of eurypterids in later (Carboniferous) estuarine environments may also be the result of regular tidal deposition. For example, in the eurypterid-bearing Hamilton and

Mazon Creek Lagerstätten, soft-tissue preservation has been inferred to have resulted from rapid sedimentation during short, sub-monthly neap-spring tide cycles (Feldman et al. 1993). Given that eurypterids are never found in completely isolated freshwater environments (e.g., inland lakes), it seems plausible that a similar control on their preservation also existed on other paleocontinents, perhaps until their extinction at the end-Permian.

Cyclicity and Preservational Facies

The regular occurrence of eurypterids above microbial structures and within shallowing- up cycles throughout the Appalachian basin suggests that fluxes in water depth are due to recurrent changes in basinal sea-level, rather than localized storm or tidal influence, and thus can be predicted over broad regional and temporal scales. The meter-scale cycles observed in the upper Silurian units described above are interpreted as largely shallowing upward parasequences.

These cycles are widely correlated (Ciurca 1978; Anderson and Goodwin 1980; Goodman et al.

1986; Elick and Siegel 2009) and show stacking patterns that may reflect periodic cycles of tens of thousands of years, nested within larger possibly eccentricity based cycles of hundred thousand durations, and thus most likely reflect allocyclic oscillations of sea level. For

141 example, based on detailed logging of a 230 m thick succession of the eurypterid-bearing

Tonoloway Formation in central Pennsylvania, Cotter and Inners (1986) documented around 34

5-to-10 meter-scale cycles. Based on the estimated overall duration of the late Silurian Přídolí

Stage, they argued that these cycles reflect Milankovitch-band and, probably processional, climate/sea level oscillations that may be bundled in 100 kya-scale eccentricity cycles marked by thickest meter-scale cycles passing upward into thinner cycles.

In the context of regular cycling of similar lithofacies across the basin, it is particularly notable that development of more offshore facies in transgressive sections of small-scale cycles was not sufficient, in itself, for production of eurypterid Lagerstätten. In the Tonoloway

Formation exposure at Allenport, Pennsylvania, ~25% of the cycles repeatedly show small microbial mounds or laminae near their transgressive bases (Cotter and Inners 1986). However, in most cases, these facies contain only minor bioturbation or, at most, bedding planes of profuse

Leperditia assemblages. Ultimately, only two cycles in the well-studied Tonoloway Formation were found to contain eurypterids, but they occur in the predicted position, immediately above thrombolitic mounds (Chapter II). Thus, while small microbial mounds appear frequently in the

Tonoloway Formation during deepening successions (cf. Eagan and Liddell 1997), ensuing conditions were evidently not adequate for inhabitation by eurypterids. We infer that, in these cases, conditions remained hypersaline throughout the depositional cycle, and evidence for this occurs in the form of evaporite molds and/or vugs and deep desiccation cracks present in these beds (Smosna et al. 1977; Cotter and Inners 1986). Under these conditions, microbialites flourished and leperditiids, interpreted as halotolerant taxa (Vannier et al. 2001), were able to proliferate, but salinity remained too high for eurypterids and other slightly more stenohaline faunas.

142

These latter cycles in the Tonoloway Formation, which lack eurypterids in the expected positions, also provide a strong case against a purely taphonomic mechanism for eurypterid preservation. A traditional view is that the association of eurypterids with evaporative facies represented carcasses of dead organisms and/or exuviae that were washed into hypersaline lagoons possibly from nearby estuaries. If this were true, then the many cycles that show definite evidence of hypersalinity should also yield excellently preserved remains. Instead, eurypterids are absent in a majority of these cycles, especially those with definite evidence of hypersalinity, e.g., the evaporitic facies of the Syracuse, Camillus, Forge Hollow formations, which comprise shales interbedded with anhydrites, gypsum, or halite. Likewise, eurypterids have never been found in further offshore (largely subsurface) evaporite facies within the Salina Group.

Implications for Eurypterid Paleoecology and Evolution

The present study confirms the traditional view that a majority of eurypterid occurrences in the Silurian are associated with generally low diversity marine or potentially brackish faunas in a mixture of siliciclastic and carbonate lithofacies. Furthermore, we agree with past suggestions that that these were largely ephemeral communities (e.g., Clarke and Ruedemann

1912; Leutze 1961), particularly those in nearshore subtidal areas that experienced brief intervals of freshening in frequently hypersaline environments (i.e., in the more basinal sections of the foreland basin during much of the Ludlow and Přídolí time).

The important question as to where these associations survived during the long intervening intervals has been considered previously (e.g., Clarke and Ruedemann 1912; Leutze

1961; Chapter III). As noted above, evidence from extensive subsurface mapping of the Salina and Bertie Groups in New York, northern Pennsylvania, and eastern Ohio (Alling and Briggs

143

1961; Rickard 1969) indicates that the deeper areas of the basin were occupied by increasingly hypersaline facies. Rickard (1969) maps concentric belts of dolostone in the nearest areas, and anhydrite and halite toward the basin center. Hence, we argue that offshore areas were an extremely unlikely area of eurypterid inhabitation during times in which they were absent from nearshore facies, and these saline facies are essentially barren, as would be expected. An alternative refugium may have existed in local regions of reduced salinity near the mouths of rivers flowing from orogenic highlands to the east, if not more open marine conditions to the southwest. The association of eurypterids and other low diversity marine faunas with presumed terrestrially derived remains—notably the early vascular plant —at several localities within the Bertie Group (e.g., the Williamsville Formation “A” Member; Edwards et al. 2004;

SJC, personal observations)—provides circumstantial evidence that some of these sections had fluviatile influence.

It has been suggested that eurypterids sought out quiet, protected environments in which to molt and/or mate, as represented by the shallow, nearshore and restricted settings in the northern Appalachian Bertie Group (i.e., the “mass-moult-mate” hypothesis, Braddy 2001; Vrazo and Braddy 2011), and this might explain their exceptional abundance in some facies. The largest mass assemblages of eurypterids are dominated by the common genus Eurypterus and are restricted to carbonate-dominated facies in the central and northern Appalachian basin (Tetlie et al. 2008; Chapter II). The “mass-moult-mate” hypothesis does not sufficiently explain the occurrence of less common eurypterid taxa that frequently occur alongside Eurypterus (e.g., dolichopterids or pterygotids), or the occurrence of older taxa in similar shallow, nearshore settings (e.g., Young et al. 2007). In the context of our preservational model, it seems likely that mass-molting or mating behavior took place during opportunistic occupation of these nearshore

144 settings as conditions allowed, i.e., following freshening during initial transgressive events, rather than when conditions were stagnant and hypersaline or briny. Thus, if the “mass-moult- mate” hypothesis applies to certain monospecific assemblages, we suggest that the initial invasion into nearshore settings for any taxon was ultimately driven by sea-level dependent processes.

More broadly, our model of inhabitation and preservation has strong implications for better understanding the eurypterid marine-to-freshwater transition that takes place over the

Paleozoic. Nearshore, evaporitic carbonate ramp settings very similar to those in the late Silurian

Appalachian basin and elsewhere (e.g., Baltica) continued to exist in Laurentia well into the

Middle Devonian (Witzke and Bunker 2006), and yet eurypterids appear to be entirely absent from these environments by this time. Conversely, once above the lowermost Devonian units in the northern and central Appalachian basin (e.g., the Manlius Formation of New York), eurypterids only occur in siliciclastic facies within increasingly terrestrially dominated environments (Plotnick 1983, 1999). This implies that while a taphonomic window for excellent eurypterid preservation continued to exist well into the mid-Paleozoic, eurypterids no longer inhabited these types of nearshore marine environments. Thus, the decline in eurypterid diversity that begins toward the end of the Silurian and continues up to the end-Devonian mass extinction may reflect a real biological signal, rather than simply a decrease of conditions conducive to preservation (cf. the Bertie-bias; Plotnick 1999). Lamsdell and Braddy (2010) concluded that an increase in competition and/or predation pressure between more marine-dwelling eurypterid taxa

(i.e., the Eurypterina) and increasingly diverse vertebrates may explain the decline of the

Eurypteridae at the beginning of the Early Devonian. The lack of eurypterids in Early Devonian,

145 nearshore carbonate settings after the Manlius Formation supports this competition hypothesis, or another biological cause.

CONCLUSIONS

Eurypterids in the Mid-Paleozoic Appalachian basin frequently co-occur with microbial structures, which we interpreted as flooding surfaces within meter-scale shallowing upward cycles (parasequences). This regular association indicates that eurypterids preferentially moved into restricted nearshore environments only during transgressive, freshening events, when conditions were near-euhaline, rather than hypersaline or briny. These cycles are often capped by sedimentary successions displaying evaporitic features such as desiccation cracks and evaporite deposits, which we interpret as indicative of sub-aerial exposure during regressions (later highstands). In areas that lack evidence for hypersalinity, eurypterids frequently occur within shallowing cycles. This cycling between freshening conditions that supported temporary inhabitation, and conditions conducive to preservation indicate that eurypterid occurrences within the Appalachian basin were largely controlled by water depth and sea-level rise and fall.

In this preservational model, the formation of eurypterid Lagerstätten in the Appalachian basin is the result of biotic (environmental preference) and abiotic (preservational) controls, but the conditions that promoted inhabitation and preservation ultimately occurred within the same location, allowing us to predict the occurrence of eurypterid-bearing horizons in similar nearshore carbonate deposits. The disappearance of eurypterids from carbonate ramp and tidal mudflat settings later in the Paleozoic, despite such settings remaining open at least into the

Middle Devonian, suggests that their absence in these environments reflects a real biological signal, rather than the closure of a taphonomic window at the end-Silurian.

146

ACKNOWLEDGEMENTS

We would like to thank Susan Butts and Jessica Utrup (YPM) for their collections assistance.

The authors would like to acknowledge Stephen Bell, Ray Garton, Trent Spielman, and Jeffrey

Trop for field assistance, specimen collection, and locality discussion. Gene Hunt, Joshua Miller,

João Martins, Carl Simpson, and Laura Soul are thanked for assistance with data manipulation and thoughtful discussion. This study was supported by grants from the University Of Cincinnati

Chapter Of Sigma Xi and the Geological Society of America.

147

REFERENCES

Alling, H.A., and Briggs, L.I., 1961, Stratigraphy of upper Silurian Cayugan evaporites: AAPG

Bulletin, v. 45, p. 515–547, doi: 10.1306/bc743673-16be-11d7-8645000102c1865d.

Anderson, E.J., and Goodwin, P.W., 1980, Helderberg PAC's, Guidebook, Society of Economic

Paleontologists and Mineralogists (Eastern Section) Field Trip, p. 32.

Barnes, R.K., 1989, What, if anything, is a brackish-water fauna?: Transactions of the Royal

Society of Edinburgh: Earth Sciences, v. 80.

Belak, R., 1980, The Cobleskill and Akron members of the Rondout Formation: late Silurian

carbonate shelf sedimentation in the Appalachian basin, New York State: Journal of

Sedimentary Research, v. 50, p. 1187–1204, doi: 10.1306/212f7ba8-2b24-11d7-

8648000102c1865d.

Bell, S.C., and Smosna, R., 1999, Regional facies analysis and carbonate ramp development in

the Tonoloway Limestone (upper Silurian; central Appalachians): Southeastern Geology,

v. 38, p. 259–278.

Boyer, J.N., 1994, Aerobic and anaerobic degradation and mineralization of 14C-chitin by water

column and sediment inocula of the York River , Virginia: Applied and

Environmental Microbiology, v. 60, p. 174–179.

Braddy, S.J., 2001, Eurypterid palaeoecology: palaeobiological, ichnological and comparative

evidence for a 'mass-moult-mate' hypothesis: Palaeogeography, Palaeoclimatology,

Palaeoecology, v. 172, p. 115–132.

148

Brett, C.E., 1995, Sequence Stratigraphy, , and Taphonomy in Shallow Marine

Environments: Palaios, v. 10, p. 597–616, doi: 10.2307/3515097.

Brett, C.E., 1998, Sequence stratigraphy, paleoecology, and evolution: biotic clues and responses

to sea-level fluctuations: Palaios, v. 13, p. 241–262, doi: 10.2307/3515448.

Brett, C.E., Allison, P.A., Desantis, M.K., Liddell, W.D., and Kramer, A., 2009, Sequence

stratigraphy, cyclic facies, and lagerstätten in the Middle Cambrian Wheeler and Marjum

Formations, Great Basin, Utah: Palaeogeography, Palaeoclimatology, Palaeoecology, v.

277, p. 9–33, doi: http://dx.doi.org/10.1016/j.palaeo.2009.02.010.

Brett, C.E., Baird, G.C., and Speyer, S.E., 1997, Fossil Lagerstätten: stratigraphic record of

paleontological and taphonomic events, in Brett, C.E., and Baird, G., (eds.),

Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications:

Columbia University Press, New York, p. 3–40.

Brett, C.E., Goodman, W.M., and Loduca, S.T., 1990, Sequences, cycles, and basin dynamics in

the Silurian of the Appalachian foreland basin: Sedimentary Geology, v. 69, p. 191–244,

doi: http://dx.doi.org/10.1016/0037-0738(90)90051-T.

Brooks, H.K., 1957, Chelicerata, Trilobitomorpha, Crustacea (exclusive of Ostracoda) and

Myriapoda, in Hedgpeth, J.W., (ed.), Treatise on Marine Ecology and Paleoecology,

Geological Society of America, p. 895–930.

Caster, K.E., and Kjellesvig-Waering, E.N., 1964, Upper Ordovician eurypterids of Ohio:

Palaeontographica Americana, v. 4, p. 297–358.

149

Ciurca, S.J., Jr., 1973, Eurypterid horizons and the stratigraphy of upper Silurian and Lower

Devonian rocks of western New York State, New York State Geological Association,

45th Annual Meeting, Brockport, New York, p. D1–D14.

Ciurca, S.J., Jr., 1978, Eurypterid horizons and the stratigraphy of upper Silurian and Lower

Devonian rocks of central-eastern New York State, in Merriam, D.F., (ed.), New York

State Geological Association, 50th Annual Meeting, Syracuse, NY.

Ciurca, S.J., Jr., 2005, Eurypterids and facies changes within the Silurian/Devonian "Eurypterid

Beds" of New York State, in Valentino, D.W., ed., New York State Geological

Association, 77th Annual Meeting, Albany, New York, p. 113–121.

Ciurca, S.J., Jr., 2013, Microbialites within the eurypterid-bearing Bertie Group of western New

York and Ontario, Canada, in Baird, G., and Wilson, M., eds., New York State

Geological Association, 85th Annual Meeting, Fredonia, New York, p. 154–179.

Ciurca, S.J., Jr., and Domagala, M., 1988, Silurian algal mound/eurypterid association, New

York State and Pennsylvania, Rochester Academy of Science 15th Annual Scientific

Paper Session, Nazareth College of Rochester, New York, p. 45.

Ciurca, S.J., Jr., and Hamell, R.D., 1994, Late Silurian sedimentation, sedimentary structures and

paleoenvironmental settings within an eurypterid-bearing sequence (Salina and Bertie

Groups), Western New York State and Southwestern Ontario, Canada, in Brett, C.E., and

Scatterday, J., eds., New York State Geological Association, 66th Annual Meeting,

Rochester, New York, p. 457–488.

150

Clarke, J.M., and Ruedemann, R., 1912, The Eurypterida of New York: New York State

Museum Memoir, v. 14, p. 1–439.

Cody, G.D., Gupta, N.S., Briggs, D.E.G., Kilcoyne, A.L.D., Summons, R.E., Kenig, F., Plotnick,

R.E., and Scott, A.C., 2011, Molecular signature of chitin-protein complex in Paleozoic

arthropods: Geology, v. 39, p. 255–258, doi: 10.1130/g31648.

Cotter, E.C., and Inners, J.D., 1986, Stop 1.5; Allenport in Sevon, W.D., ed., Selected Geology

of Bedford and Huntington Counties: Guidebook for the 51st Annual Field Conference of

Pennsylvania Geologists: Field Conference of Pennsylvania Geologists, Juniata

University, Huntington, PA, p. 27–39.

Dennison, J.M., and Head, J.W., 1975, Sealevel variations interpreted from the Appalachian

basin Silurian and Devonian: American Journal of Science, v. 275, p. 1089–1120, doi:

10.2475/ajs.275.10.1089.

Dixon, O.A., and Jones, B., 1978, Upper Silurian Leopold Formation in the Somerset-Prince

Leopold Islands type area, Arctic Canada: Bulletin of Canadian Petroleum Geology, v.

26, p. 411-423.

Dorobek, S.L., and Read, J.F., 1986, Sedimentology and basin evolution of the Siluro-Devonian

Helderberg Group, Central Appalachians: Journal of Sedimentary Research, v. 56, p.

601–613.

Dunlop, J.A., 2010, Geological history and phylogeny of Chelicerata: Arthropod Structure and

Development, v. 39, p. 124–142, doi: 10.1016/j.asd.2010.01.003.

151

Eagan, K.E., and Liddell, W.D., 1997, Stromatolite biostromes as bioevent horizons: An

example from the Middle Cambrian Ute Formation of the northeastern Great Basin, in

Brett, C.E., and Baird, G.C., (eds.), Paleontologic Events: Stratigraphic, Ecologic and

Evolutionary Implications: Columbia University Press, New York, p. 493–535.

Edwards, D., Banks, H.P., Ciurca, S.J., Jr., and Laub, R.S., 2004, New Silurian cooksonias from

dolostones of north-eastern North America: Botanical Journal of the Linnean Society, v.

146, p. 399–413, doi: 10.1111/j.1095-8339.2004.00332.x.

Elick, J.M., and Siegel, M., 2009, Paleoecology and cyclicity of the Tonoloway Formation and

Keyser Formations: A guide to understanding limestone composition in Mandata, PA:

Geological Society of America Abstracts with Programs, v. 41, p. 118.

Feldman, H.R., Archer, A.W., Kvale, E.P., Cunningham, C.R., Maples, C.G., and West, R.R.,

1993, A tidal model of Carboniferous Konservat-Lagerstaetten formation: Palaios, v. 8, p.

485–498, doi: 10.2307/3515022.

Foote, M., 2006, Substrate affinity and diversity dynamics of Paleozoic marine animals:

Paleobiology, v. 32, p. 345–366, doi: 10.1666/05062.1.

Gehling, J.G., 1999, Microbial mats in terminal siliciclastics: death masks:

Palaios, v. 14, p. 40–57, doi: 10.2307/3515360.

Goodman, P.T., Anderson, E.J., Goodwin, P.W., and Sullivan, K.S., 1986, Small-scale episodic

stratigraphic accumulation of the upper Silurian–Lower Devonian carbonate sequence in

central Pennsylvania: Geological Society of America Abstracts with Programs, v. 18, p.

19.

152

Hamell, R.D., and Ciurca, S.J., Jr., 1986, Paleoenvironmental analysis of the Fiddlers Green

Formation (late Silurian) in New York state, New York State Geological Association,

58th Annual Meeting, Ithaca, New York, p. 199–218.

Handford, C.R., and Loucks, R.G., 1993, Carbonate depositional sequences and systems tracts—

responses of carbonate platforms to relative sea-level change, in Loucks, R.G., and Sarg,

R., (eds.), Carbonate Sequence Stratigraphy; Recent Advances and Applications:

American Association of Petroleum Geologists Memoir 57, p. 3–41.

Jones, B., and Kjellesvig-Waering, E.N., 1985, Upper Silurian Eurypterids from the Leopold

Formation, Somerset Island, Arctic Canada: Journal of Paleontology, v. 59, p. 411-417,

doi: 10.2307/1305035.

Kaljo, D., 1970, The Silurian of Estonia: Institute of the Geological Academy of Science of

Estonia, Tallinn.

Kiessling, W., and Aberhan, M., 2007, Environmental determinants of marine benthic

biodiversity dynamics through Triassic– time: Paleobiology, v. 33, p. 414–434,

doi: 10.1666/06069.1.

Kirchman, D.L., and White, J., 1999, Hydrolysis and mineralization of chitin in the Delaware

Estuary: Aquatic Microbial Ecology, v. 18, p. 187–196.

Kjellesvig-Waering, E.N., and Leutze, W.P., 1966, Eurypterids from the Silurian of West

Virginia: Journal of Paleontology, v. 40, p. 1109–1122.

153

Kluessendorf, J., 1994, Predictability of Silurian Fossil-Konservat-Lagerstätten in North

America: Lethaia, v. 27, p. 337–344.

Lamsdell, J., Briggs, D., Liu, H., Witzke, B., and Mckay, R., 2015, The oldest described

eurypterid: a giant Middle Ordovician (Darriwilian) megalograptid from the Winneshiek

Lagerstatte of Iowa: BMC Evolutionary Biology, v. 15, p. 169.

Lamsdell, J.C., and Braddy, S.J., 2010, Cope's Rule and Romer's theory: patterns of diversity and

gigantism in eurypterids and Palaeozoic vertebrates: Biology Letters, v. 6, p. 265–269,

doi: 10.1098/rsbl.2009.0700.

Lau, K., 2009, Paleoecology and paleobiogeography of the New York Appalachian basin

eurypterids (undergraduate thesis): Unpublished Undergraduate thesis, Yale, New Haven,

CT, 49 p.

Leutze, W.P., 1961, Arthropods from the Syracuse Formation, Silurian of New York: Journal of

Paleontology, p. 49–64.

Loduca, S.T., and Brett, C.E., 1997, The Medusaegraptus epibole and Lower Ludlovian

Konservat-Lagerstätten of eastern North America, in Brett, C.E., and Baird, G., (eds.),

Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications:

Columbia University Press, New York, p. 369–406.

Maples, C.G., and Schultze, H.-P., 1988, Preliminary comparison of the

assemblage of Hamilton, Kansas, with marine and nonmarine contemporaneous

assemblages, in Mapes, G.K., and Mapes, R.H., (eds.), Regional Geology and

154

{aleontology of Upper Paleozoic Hamilton Quarry Area in Southeastern Kansas: Kansas

Geological Survey, Lawrence, KA, p. 253–273.

Meidla, T., Tinn, O., and Männik, P., 2014, Stop B8: Soeginina cliff, in Bauert, H., Hints, O.,

Meidla, T., and Männik, P., (eds.), 4th Annual Meeting of IGCP 591, Estonia, 10–19

June 2014. Abstracts and Field Guide: University of Tartu, Tartu, Tartu, Estonia, p. 194–

196.

Mutel, M.H.E., Waugh, D.A., Feldmann, R.M., and Parsons-Hubbard, K.M., 2008, Experimental

taphonomy of Callinectes sapidus and cuticular controls on preservation: Palaios, v. 23,

p. 615–623.

Oksanen, J., Blanchet, F.G., Kindt, R., Legendre, P., Minchin, P.R., O'hara, R.B., Simpson, G.L.,

Solymos, P., Stevens, M.H.H., and Wagner, H., 2015, Vegan: Community Ecology

Package, Ver. R package version 2.2-1, http://CRAN.R-project.org/package=vegan.

Parsons-Hubbard, K.M., Powell, E.N., Raymond, A., Walker, S.E., Brett, C.E., Ashton-Alcox,

K., Shepard, R.N., Krause, R., and Deline, B., 2008, The taphonomic signature of a brine

seep and the potential for Burgess Shale style preservation: Journal of shellfish research,

v. 27, p. 227–239.

Stratigraphic Paleobiology: Understanding the Distribution of Fossil Taxa in Time and Space,

2012,http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nla

bk&AN=439851.

155

Perga, M.-E., 2011, Taphonomic and early diagenetic effects on the C and N stable isotope

composition of cladoceran remains: implications for paleoecological studies: Journal of

Paleolimnology, v. 46, p. 203–213, doi: 10.1007/s10933-011-9532-y.

Plotnick, R.E., 1983, Patterns in the evolution of the eurypterids: Unpublished Ph.D. thesis,

Unpublished Ph.D. dissertation, University of Chicago, University of Chicago, 411 p.

Plotnick, R.E., 1999, Habitat of Llandoverian–Lochkovian eurypterids, in Boucot, A.J., and

Lawson, J.D., (eds.), Paleocommunities, A Case Study from the Silurian and Lower

Devonian: Cambridge University Press, Cambridge, p. 106–131.

Poulicek, M., Gaill, F., and Goffinet, G., 1998, Chitin biodegradation in marine environments, in

Stankiewicz, B.A., and Bergen, P.F.v., (eds.), -containing macromolecules in the

bio- and geosphere, ACS Symposium Series 707, p. 163–210.

Poulicek, M., and Jeuniaux, C., 1991, Chitin biodegradation in marine environments: An

experimental approach: Biochemical Systematics and Ecology, v. 19, p. 385–394, doi:

http://dx.doi.org/10.1016/0305-1978(91)90055-5.

R Core Team, 2015, R: A language and environment for statistical computing, Ver. R

Foundation for Statistical Computing, Vienna, Austria, http://www.R-project.org.

Rickard, L.V., 1969, Stratigraphy of the upper Silurian Salina Group: New York, Pennsylvania,

Ohio, Ontario: New York State Museum and Science Service. Geological Survery Map

and Chart series no. 12, Albany, NY, 57 p.

156

Schimmelmann, A., Deniro, M.J., Poulicek, M., Voss-Foucart, M.F., Goffinet, G., and Jeuniaux,

C., 1986, Stable isotopic composition of chitin from arthropods recovered in

archaeological contexts as palaeoenvironmental indicators: Journal of Archaeological

Science, v. 13, p. 553–566, doi: 10.1016/0305-4403(86)90040-3.

Schröer, L., Vandenbroucke, T.R.A., Hints, O., Steeman, T., Verniers, J., Brett, C., Cramer,

B.D., and Mclaughlin, P.I., 2016, A Late Ordovician age for the Whirlpool and Power

Glen Formation, New York: Canadian Journal of Earth Sciences, doi: 10.1139/cjes-2015-

0226.

Seilacher, A., Reif, W.E., Westphal, F., Riding, R., Clarkson, E.N.K., and Whittington, H.B.,

1985, Sedimentological, ecological and temporal patterns of fossil Lagerstätten [and

discussion]: Philosophical Transactions of the Royal Society of London. Series B,

Biological Sciences, v. 311, p. 5–24, doi: 10.2307/2396966.

Seki, H., and Taga, N., 1963, Microbiological studies on the decomposition of chitin in marine

environment. II. Influence of some environmental factors on the growth and activity of

marine chitinoclastic bacteria Journal of the Oceanographical Society of Japan, v. 19, p.

109–111.

Selden, P.A., 1984, Autecology of Silurian eurypterids, in Bassett, M.G., and Lawson, J.D.,

(eds.), Autecology of Silurian organisms: Special Papers in Palaeontology, The

Palaeontological Association, p. 39–54.

Smosna, R., Patchen, D., Warshauer, S., and Perry, J., W., 1977, Relationships between

depositional environments, Tonoloway Limestone, and distribution of evaporites in the

157

Salina Formation, West Virginia, SG 5: Reefs and Evaporites—Concepts and

Depositional Models: American Association of Petroleum Geologists, p. 125–143.

Stott, C.A., Tetlie, O.E., Simon, J.B., Nowlan, G.S., Glasser, P.M., and Devereux, M.G., 2005, A

New Eurypterid (Chelicerata) from the Upper Ordovician of Manitoulin Island, Ontario,

Canada: Journal of Paleontology, v. 79, p. 1166–1174, doi: 10.2307/4095002.

Swartz, C.K., and Swartz, F.M., 1930, Age of the Schwangunk conglomerate of eastern New

York: American Journal of Science, v. Series 5 Vol. 20, p. 467–474, doi: 10.2475/ajs.s5-

20.120.467.

Swartz, C.K., and Swartz, F.M., 1931, Early Silurian formations of southeastern Pennsylvania:

Geological Society of America Bulletin, v. 42, p. 621–662, doi: 10.1130/gsab-42-621.

Tetlie, O.E., 2007, Distribution and dispersal history of Eurypterida (Chelicerata):

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 252, p. 557–574, doi:

10.1016/j.palaeo.2007.05.011.

Tetlie, O.E., Brandt, D.S., and Briggs, D.E.G., 2008, Ecdysis in sea scorpions (Chelicerata:

Eurypterida): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 265, p. 182–194,

doi: 10.1016/j.palaeo.2008.05.008.

Tetlie, O.E., and Poschmann, M., 2008, Phylogeny and palaeoecology of the Adelophthalmoidea

(arthropoda; chelicerata; eurypterida): Journal of Systematic Palaeontology, v. 6, p. 237–

249, doi: Doi 10.1017/S1477201907002416.

158

Tetreault, D.K., Waddington, J., and Rudkin, D.M., 1994, Eurypterids from the lower Silurian

(Lower Llandoverian) Whirlpool Formation, southern Ontario, Fourth Canadian

Palentology Conference, Programs and Abstracts, p. 14–15.

Tollerton, V.P., Jr., 1997, Eurypterids and associated fauna at Litchfield, a classic locality, in

Rayne, T.W., Bailey, D.G., and Tewksbury, B.J., eds., New York State Geological

Association, 69th Annual Meeting, Clinton, New York, p. 253–264.

Tollerton, V.P., Jr., 2004, Summary of a revision of New York State Ordovician eurypterids:

implications for eurypterid palaeoecology, diversity and evolution: Transactions: Earth

Sciences, v. 94, p. 235-242.

Van Der Voo, R., 1988, Paleozoic paleogeography of North America, Gondwana, and

intervening displaced terranes: comparisons of paleomagnetism with paleoclimatology

and biogeographical patterns: Geological Society of America Bulletin, v. 100, p. 11–324.

Van Wagoner, J.C., Mitchum, K., Campion, K.M., and Rahmanian, V.D., 1990, Siliciclastic

sequence stratigraphy in well logs, cores, and outcrops, Tulsa, 55 p.

Vannier, J., Wang, S.Q., and Coen, M., 2001, Leperditicopid arthropods (Ordovician–Late

Devonian): functional morphology and ecological range: Journal of Paleontology, v. 75,

p. 75–95.

Viira, V., and Einasto, R., 2003, Wenlock-Ludlow boundary beds and conodonts of Saaremaa

Island, Estonia: Proceedings of the Estonian Academy of Sciences. Geology, v. 52, p.

213–238.

159

Vrazo, M.B., and Braddy, S.J., 2011, Testing the ‘mass-moult-mate’ hypothesis of eurypterid

palaeoecology: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 311, p. 63–73,

doi: 10.1016/j.palaeo.2011.07.031.

Webster, M., Gaines, R.R., and Hughes, N.C., 2008, Microstratigraphy, trilobite biostratinomy,

and depositional environment of the “Lower Cambrian” Ruin Wash Lagerstätte, Pioche

Formation, Nevada: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 264, p. 100–

122.

Witzke, B.J., and Bunker, B.J., 2006, Stratigraphy of the Wapsipinicon Group (Middle

Devonian) in southeastern Iowa: Guidebook for the 36th Annual Field Conference of the

Great Lakes Section, Society for Sedimentary Geology (SEPM), and the 67th Annual Tri-

State Field Conference, v. Iowa Geological Survey Guidebook Series No. 26, p. 47–58.

Young, G.A., Rudkin, D.M., Dobrzanski, E.P., and Robson, S.P., 2012, Great Canadian

Lagerstätten 3. Late Ordovician Konservat-Lagerstätten in Manitoba: Geoscience

Canada, v. 39, p. 201–213.

Young, G.A., Rudkin, D.M., Dobrzanski, E.P., Robson, S.P., and Nowlan, G.S., 2007,

Exceptionally preserved Late Ordovician biotas from Manitoba, Canada: Geology, v. 35,

p. 883–886, doi: 10.1130/g23947a.1.

160

FIGURES

161

FIGURE 1. Regional map of North American Appalachian basin and stratigraphic correlation chart for Silurian–Lower Devonian surface units in the Laurentian Appalachian basin. A)

Northern, central, and uppermost southern Appalachian basin. Silurian (black) and

Lower/Middle Devonian (gray) bedrock exposures are represented by the shaded area. Dashed line represents approximate position of the basin axis in the Silurian. Numbered localities correspond to stratigraphic columns in B. B) Representative stratigraphic columns for three regions within the study area in the Appalachian basin. Units are not to scale, but boundary positions are broadly comparable. Informal unit names are lowercase; for clarity, sub-members

(“S-mbr”) or beds were only included if they have yielded eurypterids or occur within eurypterid-bearing units. Angled boundary lines separate non-adjacent and laterally differentiated (E–W), but isochronous units; dashed lines indicate uncertain boundaries.

Stratigraphic data compiled from Ciurca (1978, 1990; unpublished field notes, personal observations), Brett et al. (1990), Brett et al. (1995), Inners (1997), Laughrey (1999, and references therein), and Cramer et al., 2009. Adapted from Lau (2009).

162

FIGURE 2. Microbial structures and associated eurypterids from the Silurian of the Appalachian basin. A) Stromatolite with subjacent evaporitic vugs, Tonoloway Formation, PA. Ruler in cm.

B) Thrombolitic mounds; eurypterids occur within intermound sediments, Ellicott Creek Breccia,

Fiddler’s Green Formation, Neid Rd. Quarry, NW. Compass for scale. After Ciurca, 2005. C)

Thrombolite with eurypterid (indicated by arrow) in intermound sediments, Ellicott Creek

163

Breccia, Fiddler’s Green Formation, Neid Rd. Quarry, NY. Compass for scale. D) Isolated eurypterid (Eurypterus) carapace and partial tergite adjacent to thrombolite, Williamsville

Formation, Ridgemount Quarry, ON. Ruler in cm. After Ciurca, 2013. E) Isolated pterygotid claw from within thrombolite intermound, Fiddler’s Green Formation, Neid Rd. Quarry, NY.

Scale bar = 5 cm. Modified from Ciurca, 2005.

164

FIGURE 3. Plot of first two axes of CCA of all fauna and significant environmental variables in the Silurian–Devonian Appalachian basin (n = 109). For image clarity, only samples with greatest taxonomic diversity are named (in black); remaining units are represented as gray crosses. Named units include formation, member, sub-member, and bed-level (as number). “U” suffix indicates undifferentiated member; “u” indicates undifferentiated sub-member; 0 = undifferentiated within bed; 1 = lowermost; 2 = lower; 3 = middle; 4 = upper; 5 = uppermost

(See Supplemental Table 1 for locality data). For image clarity, only the most common taxa, based on total abundance across samples, are named (in blue); remaining taxa are represented as

165 red dots. Vectors for environmental variables (p < 0.05; in green) indicate direction of increasing gradient.

166

FIGURE 4. Plot of first two axes of CCA of all fauna and significant environmental variables in the Silurian–Devonian Appalachian basin. Sample data aggregated to sub-member level, or the next available stratigraphic level (n = 65). For image clarity, only samples (as individual stratigraphic units) with greatest eurypterid diversity are named (in black); remaining units are represented as gray crosses. Named units include formation, and member and sub-member name

(if necessary for distinction). “U” suffix indicates undifferentiated position. For image clarity, only the most common taxa, based on total abundance across samples, are named (in blue); remaining taxa are represented as red dots. Vectors for environmental variables (p < 0.05; in green) indicate direction of increasing gradient.

167

FIGURE 5. Plot of first two axes of CCA of eurypterids and significant environmental variables in the Silurian–Devonian Appalachian basin. (n = 109). For image clarity, only samples (as individual stratigraphic units) with greatest eurypterid diversity are named (in black); remaining units are represented as gray crosses. Named units typically include formation, member, and sub- member name (when present); “FG” = Fiddlers Green Formation; “ECB” = Ellicott Creek

Breccia Member. For image clarity, only the most common eurypterid genera, based on total abundance across samples, are named (in blue); remaining taxa are represented as red dots.

Vectors for environmental variables (p < 0.05; in green) indicate direction of increasing gradient.

168

FIGURE 6. Cartoons of generalized eurypterid-bearing sequences observed in the Silurian–

Lower Devonian of the Laurentian Appalachian basin. Not to scale. Central column depicts relative rise and fall in water depth; PSB = parasequence boundary. A) Bertie Group-Manlius- type cycle. B) Vernon (“Pittsford”)-Bloomsburg-type cycle. C) Tonoloway Formation-type cycle. D) Wills Creek-type cycle. See text for cycle descriptions.

169

170

FIGURE 7. Cartoon of generalized depositional settings and typical facies succession within eurypterid-bearing strata in the northern Appalachian basin. Not to scale. Straight arrows indicate relative rise and fall in water depth within each setting. A) Subtidal environment, following transgression. Eurypterids and limited marine fauna are present, as are stromatolites/thrombolites. B) Generalized intertidal–supratidal environment, following regression and/or evaporation (late-HST). Evaporation (wavy arrows) begins to produce desiccation cracks. Eurypterids are absent and remains are buried. Only halotolerant organisms

(e.g., leperditicopids) are present as conditions become increasingly hypersaline and/or dysoxic.

C) Supratidal–sabkha-like environment. Continuing regression and evaporation results in hypersaline conditions and facies are barren. Supersaturation of groundwater with NaCl leads to in situ salt hopper formation in the sub-surface. Eurypterids and microbial material appear to act as nucleation points (see Chapter III, fig. 3, for examples).

171

TABLE 1. Total eurypterid and associated fauna occurrences from eurypterid-bearing beds in the

Silurian–Devonian of the Appalachian basin. Single occurrences are excluded and some generically unidentified taxa have been grouped at a higher taxonomic level, e.g., rhynchonellid brachiopods.

N = Total Occurrences Eurypterida Associated Fauna Trace fossils Acutiramus 14 7 Arthrophycus 2 Bassipterus 1 indet. 6 Chondrites 3 Buffalopterus 2 indet. 3 Gordia 2 Carcinosoma 3 Conulariid indet. 3 Drepanopterus 1 Crinoidea indet. 2 Dolichopterus 14 indet. 9 Erettopterus 6 Graptolite indet. 2 Erieopterus 11 Leperditia 17 Eurypterus 65 Lingulate brachiopods 18 Eusarcus 3 Ostracods 10 Hughmilleria 7 Phyllocarids 9 Mixopterus 2 Pseudoniscus 5 Paracarcinosoma 5 Rhynchonellid brachiopods 29 Parahughmilleria 7 5 29 Rhinocarcinosoma 4 Stylonurus 3 Tylopterella 1 Waeringopterus 9

172

TABLE 2. Results of CCA of all taxa and environmental variables for sample dataset aggregated into sub-member groupings (or next highest stratigraphic interval). Non-relevant variables are not included. Significance codes: ‘***’ = p < 0.001; ‘**’ = p < 0.01; ‘*’ = p < 0.05.

Variable CA1 Score CA2 Score r2 Pr (>r) Dolomite 0.92672 -0.37576 0.3389 *** Limestone 0.84435 0.53579 0.0228 0.4948 Calcareous shale/mudstone -0.9775 0.21093 0.0248 0.4741 Limestone (ribbony) 0.61308 0.79002 0.0117 0.6679 Micrite 0.56572 -0.8246 0.0228 0.4821 Shale -0.97869 -0.20534 0.2453 *** Mudstone 0.84945 -0.52767 0.0026 0.772 Siltstone -0.99015 0.14003 0.3562 *** Conglomerate 0.17946 0.98377 0.0384 0.2951 Sandstone -0.98825 0.15281 0.0301 0.3093 Thrombolite 0.85117 -0.52488 0.096 * Stromatolite 0.97579 0.21872 0.0472 0.2298 Algal mats 0.69732 -0.71676 0.0781 0.0824 Halite 0.69352 -0.72044 0.143 ** Gypsum 0.58961 -0.80769 0.03 0.3261 Chert 0.92121 -0.38907 0.0314 0.3716 Mudcracks 0.83201 0.55476 0.0184 0.5716 Bioturbation/Traces 0.58398 -0.81176 0.091 0.054 Ripple marks 0.65811 -0.75292 0.1058 * Starved surface 0.71245 -0.70172 0.0338 0.3184 Pyrite 0.43301 -0.90139 0.003 0.9033 Mottled 0.94664 -0.32228 0.0544 0.1523 Carbonaceous 0.5006 -0.86568 0.0059 0.8085 Breccia 0.97995 -0.19925 0.0092 0.7245 Reefal 0.72293 0.69092 0.0289 0.3904

173

Chapter V

Taphonomic Bias in Taxonomic Assignment: A Semi-Landmark Approach to Distinguishing

Species of Silurian Eurypterids

Matthew B. Vrazo1, Brenda R. Hunda2, and Carlton E. Brett1

1Department of Geology, 500 Geology/Physics Building, University of Cincinnati, Cincinnati,

Ohio 45221-0013 USA

2Collections and Research, Cincinnati Museum Center, 1301 Western Avenue, Cincinnati, OH

45203

Keywords: Eurypterus, geometric morphometrics, eurypterid systematics, Bertie Group,

174

ABSTRACT

A geometric morphometric landmark and semi-landmark analysis was performed on isolated eurypterid carapaces from the upper Silurian Appalachian basin of New York and Ontario. The utility of isolated carapaces for species-level identification is equivocal, but these remain the basis for a number of morphospecies. Using a high-resolution approach that takes into account overall carapace shape, we test the ability to distinguish purported species within two populations of eurypterids from the contemporaneous Phelps Waterlime and Ellicott Creek members of the Fiddlers Green Formation (Bertie Group). We also test the utility of a carapace embayment structure as a distinct taxonomic character for the common Eurypterus remipes

(sensu Tetlie et al., 2007) within a quantitative morphometric framework. Landmark and semi- landmark analysis reveal a strong influence of ontogeny on overall shape, consistent with previous findings. Following size-standardization, clustering of specimens that bear the embayment structure is observed, but no other clustering among morphotypes is noted. A

Canonical Variates Analysis (CVA) indicates that specimens with the embayment structure can be discriminated from those without, and supports the use of embayment structures as a taxonomic character for E. remipes. Examination of only those specimens that bear an embayment (i.e., E. cf. remipes) reveals significant morphological differences in morphology, specifically related to the position of the eye, at a regional-scale. We conclude that isolated carapaces cannot be used for species-level assignments within contemporaneous morphotypes from the same genus, unless well-defined features (such as embayments) are visible a priori.

However, within well-defined species, landmark and semi-landmark analysis provides a viable approach for characterizing morphological variety among isolated carapaces at a regional-scale.

175

INTRODUCTION

The multi-element eurypterid exoskeleton was highly prone to pre-burial disarticulation

(Tetlie et al. 2008). Although eurypterids are sometimes found fully articulated and lacking deformation (e.g. in some Lagerstätten, Kluessendorf 1994), they are typically found as disarticulated or isolated remains. The fragmentary nature of the eurypterid fossil record has therefore necessitated erection of taxa based on limited exoskeletal material; for example, isolated carapaces or prosomas, which are among the most commonly preserved body tagma

(Tetlie et al. 2008). However, the use of isolated tagma such as carapaces (also termed prosomas) for eurypterid taxonomics can be problematic. Carapaces are considered to be more prone to deformation (i.e., compaction, desiccation, and distortion) than other tagma (Tollerton 1987,

1989). Additionally, it has been shown that the shape of the eurypterid carapace varies markedly from juvenile to adult instar stages during ontogeny (Andrews et al. 1974; Brower and Veinus

1978; Lamsdell and Selden 2013). For example, in the common genus Eurypterus, the head transitions from a square or rounded shape to a more trapezoidal shape with age (Andrews et al.

1974; Brower and Veinus 1978; Plotnick 1983; Tollerton 1992b, a, 1993; Cuggy 1994). The strong influence of ontogeny on carapace shape led Tollerton (1987) to caution that failure to account for these influences may have resulted in oversplitting of eurypterid genera and species

(see Lamsdell and Selden 2013, for example). Thereafter, Tollerton (1989) suggested that the carapace may not be useful for identifying taxa below the genus level due to its proclivity toward deformation, ontogenetic shape variation, and its relatively featureless nature. More recently,

Lamsdell and Selden (2013) highlighted again the need for constraint on eurypterid ontogeny within phylogenetic analyses, particularly when faced with limited material.

176

Single, isolated carapaces nevertheless remain an accepted body section for species-level taxonomic designations. To this end, a number of studies have attempted to distinguish taxonomic variation within the carapaces of related taxa using a variety of quantitative univariate and multivariate methods, with mixed results (Scott 1971; Kues and Kietzke 1981; Plotnick

1983; Tollerton 1993; Cuggy 1994; Lamsdell and Selden 2013). The two most common

Eurypterus species, E. remipes and E. lacustris from the upper Silurian Appalachian basin of

Laurentia (Fig. 1), have received the greatest attention, most likely due to their abundance in museum collections (Kjellesvig-Waering and Heubusch 1962). The species status of E. lacustris has often been questioned (see Vrazo and Braddy 2011, for review) and this has led to a number of comparable studies of the prosomas of these taxa. Plotnick (1983), Tollerton (1992b), and

Cuggy (1994) all attempted to distinguish these species using multivariate analyses of univariate carapace metrics. Plotnick (1983) and Cuggy (1994) could not discern species-level differences in a Principal Components Analysis (PCA), whereas Tollerton (1993) could, when controlling for size. More recently, Tetlie et al. (2007) presented a suite of defining characters for E. remipes, one of which was a rounded embayment structure on the carapace margin (Fig. 2).

However, this feature has not been documented in any previous morphometric analysis of E. remipes, including those using fixed landmarks (Brower and Veinus 1978). This suggests the need for a higher resolution method that takes into account shape variation along the carapace and allows for the influence of size to be constrained.

In this study, we explore the use of landmarks and semi-landmarks to identify and constrain the influence of ontogeny on shape, and subsequent taxonomic interpretations at a regional-scale, when using only isolated carapaces. Semi-landmark analysis incorporates both traditional fixed landmark and outline/shape data into a single analysis (MacLeod 1999), and can

177 provide comparable results to landmark-only methods (Sheets et al. 2004). Eurypterid carapaces are particularly suited to semi-landmark analysis because they contain few Type 1 landmarks

(homologous structures, points of intersection) and only a handful of Type 2 landmarks (distal endpoints of a structure). Using this approach, we ask the following questions: 1) can isolated carapaces be used to distinguish eurypterids to the species-level?; 2) can we measure morphological variation in contemporaneous populations at the regional-scale? To answer these questions, we focus on morphotypes from two contemporaneous but distant populations of

Eurypterus from two members within the Fiddlers Green Formation (Bertie Group; ~420 my) of

New York and Ontario. The Eurypterus assemblages are both units are dominated by hundreds of isolated carapaces, which purportedly represent at least two morphospecies (E. O. Tetlie, personal communications, 2012). Recent revisions of the depositional environment in the

Silurian of the Appalachian basin have helped constrain eurypterid habitats in this region

(Chapter II, III) and allow for the first quantitative comparison of contemporaneous eurypterid populations at a regional-scale. The use of a quantitative geometric morphometric approach within a refined stratigraphic framework allows for a detailed examination of the taxonomic affinities of these morphotypes within each population and across the Appalachian basin.

GEOLOGIC SETTING

Eurypterids in this study come from the upper Silurian Ellicott Creek Breccia Member

(ECB) and Phelps Waterlime Member (PWM) of the Fiddlers Green Formation (Bertie Group;

~420 my), respectively (Fig. 3). These members appear to be diachronous, with the ECB interpreted as the slightly younger, western equivalent of the PWM. The ECB tongue overlies the latter in the few locations where they co-occur, such as at Phelps, NY (Ciurca 1990). Both units

178 overlie the massive, thrombolitic Victor member and underlie the barren shale and waterlime of the Scajaquada Formation (Ciurca 1990, 2013).

The PWM and ECB are lithologically similar, comprising finely laminated argillaceous dolostones (also known as waterlimes) interbedded with stromatolitic or thrombolitic beds, that were deposited in a nearshore, subtidal–intertidal setting along the eastern margin of the

Appalachian basin (Ciurca 1990, 2013). The ECB takes its name from a brecciated bed in the uppermost ECB that can be found throughout its occurrence and appears to be the result of evaporite dissolution (MBV, personal observations), a seismite (cf. Ciurca 2011), or both. The

PWM lacks the breccia but contains mudcracks in the uppermost beds that are absent in the

ECB. Both units contain evaporitic structures (salt hopper pseudomorphs and halite molds) that often occur on the same horizon as eurypterid remains. These structures have informed previous interpretations of the ECB depositional environment (and eurypterid habitat) as highly hypersaline (e.g., Vrazo et al. 2013), but have since been shown to be most likely the result of early stage diagenesis, rather than representative of conditions at the time of burial (Chapter II).

Eurypterids are abundant throughout both units, but tend to be the most common in the middle beds (Samuel J. Ciurca, personal communications, 2014) and generally in beds overlying microbial structures (see Chapter IV). In Chapter II and III, this co-occurrence was attributed to a preference of eurypterids for fresher conditions that follow flooding events. Three eurypterid genera are known from the ECB (Eurypterus, Dolichopterus, and Pterygotus). The same genera are found in the PWM, along with three additional genera: Acutiramus, Buffalopterus, and

Paracarcinosoma. In both members, Eurypterus is by far the most common. Tetlie et al. (2007) considered there to be two species of Eurypterus in the PWM: E. remipes, and another unidentified species (possibly a pre-cursor to E. dekayi). In the ECB assemblage, E. remipes

179 occurs along with the rare E. laculatus, (Samuel J. Ciurca, Jr., personal communication, 2013).

In addition to eurypterids, both members also contain a variable diversity of associated fauna.

Diversity within the ECB is extremely low and associated fauna of common leperditian arthropods (Leperditia), unidentified ostracod-like arthropods (most likely leperditicopids), and rare phyllocarids, brachiopods, and cephalopods. The PWM contains a similar but more diverse fauna that includes gastropods, corals, notable early scorpions, rare large alga (Medusaegraptus), and early plants (Cooksonia) (MBV, personal observations).

A vast majority of the specimens collected from either unit comprises isolated carapaces, or carapaces with only the first few pre-abdominal tergites attached. Tetlie et al. (2008) and others have noted the propensity for molts to become disarticulated at the base of the carapace, or first tergite, from a variety of depositional settings. Only a very small percentage of specimens have articulated post-abdominal tergites or bear appendages, a pattern that further supports their status as post-ecdysal molts (Tetlie et al. 2008; Vrazo and Braddy 2011). Nevertheless, the highly disarticulated nature of the assemblage suggests that molts were subjected to biostratinomic processes to some degree prior to burial (e.g., wind-driven tides, minor storms)

(cf. Tetlie et al. 2008). “Windrows” (depressions containing accumulated eurypterid remains;

Ciurca 1978) and small-scale cross-bedding (Hamell and Ciurca 1986) have been cited as evidence for current-driven deposition in the PWM. Tetlie et al. (2008) carried out a taphonomic census on Eurypterus from the ECB and PWM at various localities including Litchfield, NY, and a site proximal to Ridgemount Quarry ON. They concluded that most eurypterid specimens in the PWM and ECB are molts, rather than carcasses, that may have undergone some pre-burial transport. However, it has been argued that specimens probably underwent minimal transport

180 overall and were deposited relatively near the site of ecdysis (Vrazo and Braddy 2011), in which case they should ultimately be considered a parautochthonous assemblage.

METHODS AND MATERIALS

All specimens used in this study (N = 820) are members of the common eurypterid genus

Eurypterus collected by Samuel J. Ciurca, Jr. from the 1970s to present. They are currently housed in the Yale Peabody Museum (YPM) Ciurca Collection, which comprises 10,000+ specimens of eurypterids and associated fauna. No a priori species designations were assigned to specimens prior to analysis. ECB specimens were collected from two geographically proximal localities: Ridgemount Quarry, Ft. Erie, ON (42°55'21.98"N/79° 0'44.02"W), and Glen Falls

Park, Williamsville, NY (42°57'53.74"N/78°44'41.45"W), which is ~22 km east of Ft. Erie.

PWM specimens were collected from Litchfield, NY (42°58'0.37"N / 75° 7'47.27"W), which is approximately 300 km due east of Williamsville, NY.

All eurypterids were photographed at the YPM using a Nikon D5100. Prior to photographing, specimens were positioned to be as medially and laterally flat as possible, regardless of whether the specimen was completely compressed, or retained three-dimensional topology. Specimen photographs were then cropped and vertically aligned along a 90° axis in

ImageJ (Rasband 2011) using the base of the carapace and posterior end of the eyes as reference points. Carapace length and width measurements were taken from the central midline axis and widest point at the base of the carapace, respectively, to the nearest 0.01 millimeters. For specimens consisting of part and counterpart, measurements were taken from both, and then averaged. A t-test was then performed to determine if difference in mean length were statistically significant (see Appendix, Chapter V Table 1 for raw measurements). To calculate the degree of

181 univariate measurement error and landmark and semi-landmark digitization error due to specimen placement prior to photographing, two specimens with small and medium carapace lengths (~5 mm and ~26 mm) were mounted, photographed, removed, and replaced a total of 10 times (see Webster and Sheets 2010). Carapace length and width measurements were then taken in ImageJ followed by landmark and semi-landmark digitization in TPSDig2 (Rohlf 2013).

Variance and 95% confidence intervals following bootstrapping to a large number (1600) were calculated on the univariate measurements and landmark and semi-landmark positions following superimposition and removal of excess semi-landmarks (see below). For both univariate and multivariate metrics, intra-specimen measurement error was at least two degrees of magnitude smaller than that within the entire sample (Table 1), and thus considered negligible. Landmark

#7 (a Type II landmark; see below) had the greatest influence on intra-specimen variance among the test specimens above, most likely due to the extremely shallow angle of the outer curvature of the eye. However, within the whole sample, the variance contributed by landmark # 6 was similar to three other eye-based landmarks and it contributed less variance than landmark #4 (the point of maximum curvature of the anterior of the eye) and so was retained for subsequent analyses.

Most specimens in the PWM and ECB are extremely well preserved and often retain their original convex topology. Nevertheless, thin, flexible, and non-biomineralized cuticle is readily prone to pre- and post-burial distortion and/or compression. It is therefore assumed that biostratinomic or taphonomic processes have caused some degree of distortion/compression in almost all specimens. Tollerton (1987), suggested a number of readily visible features that might be considered evidence for taphonomic deformation and specimens containing any of these criteria were excluded from subsequent analyses. Because more subtle distortion may not be

182 visible at the macro scale, potential carapace deformation was quantified using the difference between the angle of the true anterior-posterior axial midline of the specimen (i.e., from the point of maximum curvature at the anterior of the carapace to the point of maximum curvature at the base of the carapace) and an idealized 90° axis running through the middle of the specimen. For most specimens, the difference between the axial midline angle and the 90° axis is <1° (see Fig.

4, for example), whereas the angle between the axial midline and 90° axis is typically > ±2° on visibly distorted/skewed specimens. Thus, a midline axial angle > ±1.5° from the 90° axis was chosen as the threshold at which specimens were considered to be too distorted or skewed for inclusion in the subsequent landmark/semi-landmark analysis (see Appendix Chapter V Table 1).

Landmark and semi-landmark digitization for all specimens was performed in TPSDig2

(Rohlf 2013). Landmark positions were chosen following those used by Brower and Veinus

(1978) with some modifications. Landmarks #1 and #2 were placed at the point of maximum curvature of the anterior and posterior of the carapace, and at the intersection of the carapace margin with the posterior of the carapace (#3) (Fig. 4). For systematic placement, landmark #1 and #2 were digitized at the corresponding start and end of the axial midline used to measure carapace length. Four landmarks were placed around the eyes. These represent the point of maximum curvature at the posterior and anterior of the eye of the eye (#4 and #5, respectively), and the point of maximum curvature of the inner and outer eye (#6 and #7, respectively). The carapace landmarks digitized by Brower and Veinus (1978, #2 and #3 in fig. 2) were not used here because these are not homologous points and essentially mirror the position of the eyes.

Following landmark digitization, a partial curve beginning and ending at fixed landmarks

(#7 and #3, respectively) and comprising 50 semi-landmarks was digitized along the carapace margin (Fig. 4). Iterative testing revealed that an outline consisting of 50 semi-landmarks was

183 necessary to represent the actual carapace perimeter length to an accuracy of ≥ 99%. This value is highly conservative; the length of the eurypterid carapace perimeter can be represented by far fewer semi-landmarks and still retain >95% accuracy (see MacLeod 2013). Semi-landmark placement on a curve can be carried out using several methods (see Sheets et al. 2004); we chose to use the equal distance function provided in TPSDig2. This function equally spaces each semi- landmark along the curve, which gives equal variance weighting to all semi-landmarks within a curve, regardless of the degree of curvature (see MacLeod 2013 for discussion). Specimens were then transformed into Procrustes superimposition using CoordGen8 (Fig. 5), part of the

Integrated Morphometrics Package (IMP8; Sheets 2014a).

Semi-landmarks only have two degrees of freedom, whereas traditional fixed landmarks have four. This means that, within a multivariate analysis, single semi-landmarks cannot explain as much variance as single fixed landmarks (Zelditch et al. 2012a). However, semi-landmarks and fixed landmarks are not recognized as separate landmark types in many software packages, and are thus weighted equally within subsequent analyses. This can significantly influence results, particularly in analyses where the number of semi-landmarks is greater than that of the fixed landmarks, as in the present study. To reduce the potential semi-landmark variance bias, the total number of semi-landmarks was reduced a priori through the use of “helper” points, which are used to replace semi-landmarks (Sheets et al. 2004) (Fig. 5). The number of helper points (and thus, the remaining number of semi-landmarks used for statistical analysis) was determined iteratively, through visual inspection of a principal components analysis (PCA). PCs of each iterative configuration of helper points and semi-landmarks were visually compared and the number of helper points—a multiple of the semi-landmark count—was increased until PC 2

(which appears to reflect shifts in the shape of the curve) yielded a range that was within the

184 range of known specimens (i.e., not distorted beyond biological reality). This process resulted in the retention of 25 semi-landmarks. Because the position of the first and last semi-landmarks matched fixed landmarks #2 and #3, respectively, the former point was removed from the dataset before subsequent analyses. This resulted in a final semi-landmark count of 24.

Many specimens lack the right or left corner of the prosoma, most likely due to pre-burial agitation. Similarly, eyes are often torn away from the exoskeleton, and, even when present, eye positions are often not symmetrical due to subtle variations in carapace topology. For this reason, specimens were not symmetrized prior to multivariate analyses because symmetrization creates artificial placement of eyes, even where distortion is not present. To maximize sample size in cases where prosomal corners or eyes were missing, the undistorted side of a specimen (i.e., the left) was digitized and then reversed and combined with the larger sample (cf. Zelditch et al.

2012b). Landmark placement error can result from handedness during digitization, but the sub- sample of “flipped” samples was small enough that potential influence on subsequent analyses was considered negligible.

The results of previous studies of eurypterid ontogeny indicate that carapace shape may be strongly influenced by ontogeny. Because changes due to ontogeny could be misconstrued as taxonomic shape variation or disparity, they must be characterized (and removed) prior to subsequent taxonomic analyses. The influence of size on overall morphology in univariate shape space is quantified by regressing Procrustes distance (i.e., distance of an individual from the group mean following Procrustes superimposition; a measure of variation in each sample) onto natural log (Ln) centroid size (quantified from distance of landmarks/semi-landmarks from the specimen center). To reduce or remove ontogenetic influence on shape, a size-standardization is necessary. We used the standardize function in Regress8 (Sheets 2014b). Following Procrustes

185 superimposition, this method regresses Ln-standardized specimens within a sample against a target size (e.g., the largest specimen within either sample).

All bivariate and multivariate analyses were carried out in IMP8 (Sheets 2014a).

Statistical analyses within multivariate shape space were performed using warp scores, which are derived from thin-plate spline decomposition (Zelditch et al. 2012a). PCA and canonical variates analysis (CVA) of these warp scores were used to visualize variation between samples.

Following resampling (bootstrapping or jackknife), tests of significance in multivariate shape space were performed using Goodall’s F-test, a test of non-parametric multivariate means

(Zelditch et al. 2012a).

RESULTS

Size-frequency distributions of all PWM and ECB specimen carapace lengths are shown in Figure 5. Size-frequency ranges for the PWM (N = 147; range: 6.47–43.46 mm; mean = 21.01 mm; SD = 8.01) and ECB (N = 422; range: 2.97–56.65 mm; = 12.28 mm; SD = 6.02) are similar, but the mean ECB specimen length is almost half that of the PWM and is significantly lower (t-test, p < 0.001). The data are continuous, which is consistent with previous studies of carapace length in the Fiddlers Green Formation (e.g., Vrazo and Braddy 2011). Vrazo,

Kaneshiro, and Matter (in prep; unpublished data) analyzed clustering of eurypterid instars using a mixture model from several intervals, including in the ECB and PWM, and were able to identify a maximum of four and five instar clusters, respectively (but see Andrews et al. 1974).

Figure 6A shows separate composites of all specimens from the PWM and ECB following Procrustes superimposition and removal of helper points (see above). A jackknife of variance of individual landmarks and semi-landmarks following Procrustes superimposition and

186 removal of helper points (Fig. 7) indicates that the fixed landmarks at the base and corner of the carapace (# 1, #3), and around the eyes (#4–6), contribute the greatest amount of variance to both the PWM and ECB samples. Table 1 contains summary statistics for both samples following

Procrustes superimposition and reduction of semi-landmarks using helper points. Variation in general size between the two populations is indicated by the difference in mean centroid size of the PWM sample, which is almost twice that of the ECB. Variance in multivariate shape space also differs significantly between the two populations, with less overall variance in the PWM sample. Figure 6B shows overlapping Procrustes composites for the PWM and ECB samples

(left) and their respective Procrustes means shapes (right), which are significantly different

(distance between means: 0.0470; F-score = 125.96, 1600 bootstraps, p < 0.001). Visual inspection of the overlapping Procrustes composites and mean shapes (Fig. 6B, left and right) reveals differences primarily in terms of the position of the eye. The Procrustes mean shape of the eye for the ECB sample is larger, and is positioned anteriorly and laterally closer to the carapace margin, than that of the PWM. Differences in the shape of the carapace margin between the PWM and ECB Procrustes composites and mean shapes are more subtle. The PWM sample composite (Fig. 6B, left) appears to exhibit less overall dispersal of individual semi-landmarks along the carapace margin. The PWM Procrustes sample composite and mean shape are also noticeably wider at the base, and more narrow in the region lateral to the eye. These result in a more trapezoidal carapace shape, compared to the slightly more subquadrate shape observed in the ECB Procrustes sample composite. Similar differences in carapace shape have been previously noted between older and younger instar stages in Eurypterus, respectively (e.g.,

Andrews et al. 1974). Notably, both samples show similar increased distribution of semi- landmark points in the region of the curve lateral to the eye (Fig. 6B, left). Variation in the shape

187 of the lateral carapace margin has previously been used to delineate different species (Tetlie et al.

2007) and this will be explored further below.

A plot of the first two PCs from a PCA of all specimens from both populations is presented in Figure 8A. Both samples overlap and no clustering is seen in either population.

Individual vector plots for the first three PC scores (following Procrustes superimposition) are presented in Figure 8B–D. PC 1 explains ~44% of all variance and primarily reflects the position of the eye relative to the anterior-posterior of the carapace, which has been tied to overall length

(i.e., ontogeny) in previous studies (Plotnick 1983; Cuggy 1994). PC 2 explains ~19% of all variance and primarily reflects the lateral position of the eye relative to the carapace margin, which again is tied to overall size. PC 3 explains ~14% of all variance and appears to primarily reflect changes in the carapace morphology. A regression of Procrustes distance on Log Centroid size confirms that the influence of ontogeny on shape is significant within both the PWM and

ECB populations (PWM, F-score: 34.35, 1600 bootstraps, p < 0.001; ECB, F-score: 32.03, 1600 bootstraps, p < 0.001; smallest three specimens used as reference) and explains 26% and ~16% of total shape variance, respectively (Fig. 9). The relationship between size and shape is stronger for the PWM population, however, and there is a significant difference in the slopes for either population (p < 0.0001).

Vector and deformation plots reflecting ontogeny-related shape variation are presented in

Figure 10. The most visible ontogeny-related variation appears to occur within the position of the eye relative to the carapace margin. Within both populations, the eye shifts from the lateral carapace margin and toward the posterior of the prosoma with increased size. Two differences between the ontogenetic trends of either population are also observed. Firstly, the eurypterid eye position within the ECB sample (Fig. 10B) appears to shift more toward the posterior of the

188 prosoma than that of the PWM sample. Secondly, the ECB population (Fig. 10A) exhibits greater variation along the carapace margin; this is particularly visible in the deformation grid

(Fig. 10A, right). This variation appears to correspond to the position of the embayment feature noted by Tetlie et al. (2007).

Having identified that ontogeny exerts a significant influence on shape in both samples, we carried out a size-standardization on each sample. A PCA of all specimens following size- standardization reveals only loose clustering of the PWM sample in the center of a plot of the first two PCs (Fig. 11A). Vector plots for the first three PCs are presented in Figure 11B–D.

Scores along PC 1, which explains 41% of all variance, appear to reflect a slight shift in the eye along the central axis, whereas PC 2, which explains 23% of all variance, appears to reflect a more lateral shift in the eye position, and slight variation along the carapace margin. PC 3 explains 13% of variance and shows an increase in carapace base width combined with increasing pronouncement of the area of the carapace associated with the embayment, as well as a lateral shift in the eye. An F-test of the means of each sample following size-standardization indicates that they remain significantly different (F-score: 42.88, 1600 bootstraps, p < 0.001), although new distance between means (0.0281) is almost half the distance between the non- standardized specimens. To identify whether or not shape variation along the carapace margin

(i.e., as an embayment structure) relates to a possible taxonomic character, or is simply the result of relative ontogenetic shape variation between the two populations, specimens with a visible embayment feature (cf. Tetlie et al. 2007) were tagged prior to subsequent analysis of individual samples.

A plot of the first two PC scores from a PCA of the PWM sample following size- standardization reveals very loose clustering of specimens that do not bear the embayment

189 feature in the upper right quadrant (Fig.12A). PC 1 and PC 2, which are presented as vector plots in Figure 12B–C, explain very similar amounts of variance (31.6% and 27.9%, respectively). In both PCs, a shift in the position of the eye is visible, as is an increase in the prominence of the embayment structure. PC 3 (Fig. 12D) explains 13% of the total variance and shows a strong lateral shift of the eye toward the center of the carapace. A plot of the first two PCs from a PCA of the ECB population following size-standardization reveals similar clustering of specimens that bear the embayment feature (Fig. 13A). The amount of variance explained by PC 1 (49.8%) and

PC 2 (18.2%) are less similar, however, to the PWM PCA scores. PC 1 scores, represented by the vector plot in Fig. 13B, primarily reflect a shift in the eye along the central axis, although some variation in the shape of the carapace margin is present. Conversely, variation in the lateral carapace morphology is more pronounced in PC 2 (Fig. 13C) and suggests a widening of the carapace at the base. PC 3 (Fig. 13D) explains 10% of total variance and shows a strong lateral shift of the eye toward the center of the carapace, similar to the PWM sample. In addition, a strong widening of the carapace base is also observed, which is not present in the PWM sample.

A plot of overlapping Procrustes mean shapes of samples in the ECB with and without the embayment structure offers further visualization of the morphological differences between the shape of the lateral carapace margin as it relates to the presence of an embayment, and the position of the eye between these sub-groups (Fig. 14).

To further explore the potential utility of the embayment structure for taxonomic identification between the two groups, the PWM and ECB samples were reduced to only those specimens that bear a visible embayment structure following Procrustes superimposition. The two sub-samples were then combined and size-standardized together to the largest specimen on the a priori assumption that growth patterns should be similar across either population. Summary

190 statistics for variance are presented in Table 2. A plot of the overlapping Procrustes means for each sub-sample is presented in Figure 15. Visual examination of the sub-sample means reveals that the carapace margins are very similar in shape, and that only the lateral position of the eye differs between them. An F-test on sub-sample means indicates that they are significantly different (F-score: 14.12, 1600 bootstraps, p < 0.001), although the difference between the sub- sample means (0.017) is less than that the difference between the total samples. A plot of the scores for the first two PCs of a PCA and their respective vector plots of the embayment-bearing

PWM and ECB sub-samples following size-standardization is presented in Figure 16. PC 1, which explains 32.4%, of all variance, reflects the shift of the eye along the carapace axis, while

PC 2, which explains 21% of all variance, reflects a lateral shift of the eye toward to the carapace center and margin. PC 3 (Fig. 16D) explains 12% of the total variance and appears to reflect eye movement toward the center of the carapace, as noted from the Procrustes means, as well as slight variation in the pronouncement of the embayment structure.

A CVA was then carried out on the two sub-samples to examine morphological differences at the regional scale (Fig. 17A); this yielded one distinct CV (Bartlett’s test: Wilk’s Λ

= 0.2603, χ2 = 150.7451, p < 0.001). A jackknife assignment test assigned specimens to their correct group 79% of the time, with a 51% rate of random correct assignment (Table 3). When the trials were increased to a high number (1000), and 10% of specimens were classified as

“unknowns”, 75% of specimens were assigned correctly, further supporting discrimination of these groups. Visual inspection of CV 1 and CV 2 deformation plots (Fig. 16B–C) reveals that both CVs primarily reflect variation related to the position of the eye relative to lateral carapace margin, and only minor variation related to the carapace shape. To identify the potential for taxonomic discrimination of specimens based on the embayment structure, a final confirmatory

191

CVA was carried out on all specimens, where two groups were identified a priori, based on the presence or absence of an embayment. In 1000 trials in which 10% of specimens were classified as “unknowns”, 89% of the assignments were correct.

DISCUSSION

The use of a combination of landmarks and semi-landmark analysis appears to be an effective methodology for characterizing eurypterid carapace ontogeny and morphology at a high-resolution. With a semi-landmark curve, we have been able to constrain variation in carapace shape due to ontogeny that was documented in previous univariate metric or fixed landmark-based analyses. Results from the linear regression of Procrustes distance on Ln centroid size confirm the strong influence of ontogeny on Eurypterus carapace, which has been well-documented previously (Andrews et al. 1974; Brower and Veinus 1974; Brower and Veinus

1978; Plotnick 1983; Tollerton 1993; Cuggy 1994). This reaffirms the critical need for constraint of this ontogenetic influence prior to considering any aspect of eurypterid taxonomy (cf.

Tollerton 1993; Lamsdell and Selden 2013). The ECB specimens are predominantly smaller than those from the PWM, and potentially comprise a larger number of slightly younger instars.

Nonetheless, the reduction in distance between the PWM and ECB sample means following size- standardization indicates that shape variation due to ontogeny can be significantly factored out.

Following characterization of the ontogenetic influence on shape, any subsequent variance observed within the populations can be assessed in terms of taxonomic significance.

After size-standardization, the embayment structure appears to exert a strong influence over the position of individual specimens in the PCA plots for both samples. Although there is some overlap in the PCA plots of specimens with and without the embayment structure, the high

192 probability of correct assignment within the subsequent CVA would seem to offer quantitative support for the use of embayment in the prosomal margin as a discriminating feature, and one taxonomic character for E. remipes (sensu Tetlie et al. 2007).

If we conclude that E. remipes carapaces can be identified by the presence of an embayment structure, this then leaves open the question of the taxonomic status of the remaining specimens. Specimens that lack an embayment in the PWM and ECB samples may represent E. laculatus, or some other morphospecies (e.g., a precursor to E. dekayi, cf. Tetlie et al. 2007).

Kjellesvig-Waering’s (1958, p. 1126–1127) diagnosis for E. laculatus refers to a “highly arched” and “quadrilateral” prosoma and “conspicuous depression surrounding the visual area of the eyes”. Only the depressions around the eye cannot be ascribed to potential ontogenetic variation within Eurypterus (cf. Andrews et al. 1974). However, during the present study, these structures were only clearly observed in a few specimens from the entire ECB sample (N = 533). Among those, some specimens only contained the depression on one side, suggesting that it is simply a taphonomic artefact following compression of the carapace, rather than a homologous structure.

This suggests that the species status of E. laculatus should be reevaluated. This view is in agreement with Plotnick (1983), who concluded that support for the species status of E. laculatus was weak based on a CVA of its carapaces measurements.

If we discount the characters described by Kjellesvig-Waering (1958), there is nevertheless noticeable variation in the position, and, to a lesser degree, shape of the eye on PC 2

(in Fig. 12 and 13), and in the Procrustes mean shapes (Fig. 14), largely in the anterior-posterior direction in both the PWM and ECB samples. Given that the variance explained by this PC is nearly the same as PC 1, this morphological heterogeneity in the position of the eye may be the basis for characterizing additional morphotypes. While the use of eye shape to identify taxa

193 below the genus level remains uncertain (Tollerton 1989), the position of the eye has been used to distinguish closely related species (E. remipes from E. lacustris; Tollerton 1993) (although this was later challenged by Cuggy [1994]). That being said, the poor clustering of non- embayment bearing specimens in either the PCA of the total PWM (Fig. 14A) or ECB (Fig. 15A) samples ultimately do not provide strong grounds of support for species-level discrimination or classification of these specimens based solely on the position or shape of the eye. Additional post-prosomal material is necessary to fully assess the taxonomic significance of this feature. It is also possible that the high variance within the non-embayment-bearing specimens from the

ECB (and the PWM) simply reflects high intra-specific variability in eye position, and a continuous character state due to increased sampling of one particular morphotype. Highly variable character states within a single fossil arthropod taxon from well-defined horizons have been noted previously in populations of the trilobite Dikelocephalus (Hughes 1994; Labandeira and Hughes 1994). The continuous nature of various characters and large intra-specific variance within a large sample of specimens of this genus had led to earlier (overzealous) oversplitting and led Hughes (1994) to synonymize 25 species into one.

The variability seen within the ECB specimens may also reflect a greater degree of time averaging within that unit. Specimens from both the PWM and ECB were collected from throughout their respective intervals and it is certainly possible (likely, even) that the samples used in this study represent more than one population. Hunt (2004a, b) found that morphological variance increased with increased time-averaging; given that both the total ECB sample, and the embayment-bearing sub-sample, exhibit greater variance than the equivalent PWM samples, this might indicate that deposition of the ECB took place over a longer timeframe. In further considering differences in depositional environment and taphonomy, it is also conceivable that

194 this anterior-posterior variation in the position of the eye within non-embayment-bearing specimens reflects minor contortion within otherwise non-visibly distorted carapaces, rather than taxonomic variation. It is interesting to note that specimens from the ECB (inclusive of all specimens, including those not used for the morphometric analysis) exhibit a wider range of axial offset angles (±5°) compared to those from the PWM (±~3.5°), which might reflect a greater degree of overall deformation (if only a cursory one). The axial offset threshold method that we employed to distinguish distorted specimens would not have excluded specimens that may have been slightly elongated along the carapace midline axis, although fossil specimen compression is more likely rather than lateral expansion (Briggs and Williams 1981) and thus probably not a significant influence here.

Returning to the question of the taxonomic utility of isolated carapaces, out results suggest that they can be used to identify specimens to the species-level, but only when discernable, discriminatory characters (i.e., embayments) are present. This is generally in agreement with Tollerton (1987, 1989), although we note the potential for exceptions, as we have described above. We are also in agreement with Plotnick (1983), who questioned the species status of several equivocal Eurypterus species that were all erected from isolated carapaces. Although Plotnick’s study was based on univariate measurements and did not have the stratigraphic constraint of the present study, their results, like ours, suggest that caution is needed when assigning taxonomic classifications to limited or relatively featureless eurypterid remains.

If the use of isolated carapaces for distinguishing poorly defined morphotypes within genetically related taxa remains equivocal, there appears to be better support for their use when quantifying intra-specific phenotypic variation within well-defined taxa. Restricting our analysis

195 to the sub-samples of E. cf. remipes (sensu Tetlie et al. 2007) allowed for regional-scale comparisons among delineated taxonomic groups. Within the Procrustes mean shapes (Fig. 15) and CVA plot (Fig. 17) of these two sub-sample groups, little variation is seen in the lateral carapace morphology, whereas prominent variation is seen within the position of the eye. This suggests some degree of vicariance within two eurypterid sub-populations of E. remipes that has not been observed previously. If the use of the position of the eye remains equivocal in terms of distinguishing lower-level taxa (cf. Tollerton, 1989), the present findings suggest that it may be useful for identifying intra-specific variation over a regional scale, all else being equal.

Geographic phenotypic variation within other Paleozoic arthropods (trilobites) has been documented using landmarks (Hopkins and Webster 2009; Witte and Yacobucci 2015). Our results suggest that integration of semi-landmarks with landmarks provides a high-resolution method for characterizing eurypterid carapace shape within well-defined taxa across broad geographic scales. Future studies should employ this approach when considering genetic or intra- specific variation over regional or temporal scales.

CONCLUSION

Isolated carapaces cannot be used reliably to distinguish closely related species, even when their morphology is characterized at a high resolution. This is in agreement with Tollerton

(1987, 1989) and earlier authors who considered carapace morphology taxonomically informative no higher than the genus-level. Caution should be used when assigning isolated carapaces to higher taxonomic levels. However, if carapace specimens are from well-defined taxa, a combined semi-landmark and landmark approach can be a viable method for characterizing regional-scale morphotypes and intra-specific variation.

196

ACKNOWLEDGEMENTS

We would like to thank Susan Butts and Jessica Utrup (YPM) for their collections assistance.

Samuel J. Ciurca, Jr. is thanked for field assistance and specimen discussion. We are grateful to

David H. Sheets for IMP software guidance and assistance with data manipulation. Gene Hunt provided helpful discussion and suggestions. Victor Tollerton, Jr. is thanked for valuable input and suggestions regarding eurypterid taphonomy. Gary Motz and Eric Tetlie are acknowledged for initial discussions that led to the fruition of this study. This study was funded by grants to

MBV from the Geological Society of America, the Schuchert and Dunbar Grant-in-Aid Program

(Yale Peabody Museum), and the Department of Geology Caster Fund (University of

Cincinnati).

197

REFERENCES

Andrews, H.E., Brower, J.C., Gould, S.J., and Reyment, R.A., 1974, Growth and variation in

Eurypterus remipes DeKay: Bulletin of the Geological Institution of the University of

Uppsala. New Series, v. 4, p. 81–114.

Briggs, D.E.G., and Williams, S.H., 1981, The restoration of flattened fossils: Lethaia, v. 14, p.

157–164, doi: 10.1111/j.1502-3931.1981.tb01918.x.

Brower, J.C., and Veinus, J., 1974, The statistical zap versus the shotgun approach:

Mathematical Geology, v. 6, p. 311–332.

Brower, J.C., and Veinus, J., 1978, Multivariate analysis of allometry using point coordinates:

Journal of Paleontology, v. 52, p. 1037–1053, doi: 10.2307/1303849.

Ciurca, S.J., Jr., 1978, Eurypterid horizons and the stratigraphy of upper Silurian and Lower

Devonian rocks of central-eastern New York State, in Merriam, D.F., (ed.), New York

State Geological Association, 50th Annual Meeting, Syracuse, NY.

Ciurca, S.J., Jr., 1990, Eurypterid biofacies of the Silurian–Devonian evaporite sequence:

Niagara Penninsula, Ontario, Canada and New York State, in Lash, G.G., ed., New York

State Geological Association, 62nd Annual Meeting, Fredonia, New York, p. D1–D23.

Ciurca, S.J., Jr., 2011, Silurian and Devonian eurypterid horizons in upstate New York, in

Nelson, N., ed., New York State Geological Association, 83rd Annual Meeting,

Syracuse, New York, p. 139–151.

198

Ciurca, S.J., Jr., 2013, Microbialites within the eurypterid-bearing Bertie Group of western New

York and Ontario, Canada, in Baird, G., and Wilson, M., eds., New York State

Geological Association, 85th Annual Meeting, Fredonia, New York, p. 154–179.

Cuggy, M.B., 1994, Ontogenetic variation in Silurian eurypterids from Ontario and New York

State: Canadian Journal of Earth Sciences, v. 31, p. 728–732, doi: 10.1139/e94-065.

Edwards, D., Banks, H.P., Ciurca, S.J., Jr., and Laub, R.S., 2004, New Silurian cooksonias from

dolostones of north-eastern North America: Botanical Journal of the Linnean Society, v.

146, p. 399–413, doi: 10.1111/j.1095-8339.2004.00332.x.

Hamell, R.D., and Ciurca, S.J., Jr., 1986, Paleoenvironmental analysis of the Fiddlers Green

Formation (late Silurian) in New York state, New York State Geological Association,

58th Annual Meeting, Ithaca, New York, p. 199–218.

Hopkins, M.J., and Webster, M., 2009, Ontogeny and geographic variation of a new species of

the corynexochine trilobite Zacanthopsis (Dyeran, Cambrian): Journal of Paleontology, v.

83, p. 524–547.

Hunt, G., 2004a, Phenotypic variance inflation in fossil samples: an empirical assessment:

Paleobiology, v. 30, p. 487–506, doi: 10.1666/0094-

8373(2004)030<0487:pviifs>2.0.co;2.

Hunt, G., 2004b, Phenotypic variation in fossil samples: modeling the consequences of time-

averaging: Paleobiology, v. 30, p. 426–443, doi: 10.1666/0094-

8373(2004)030<0426:pvifsm>2.0.co;2.

199

Kjellesvig-Waering, E.N., 1958, The genera, species and subspecies of the family Eurypteridae,

Burmeister, 1845: Journal of Paleontology, v. 32, p. 1107–1148.

Kjellesvig-Waering, E.N., and Heubusch, C.A., 1962, Some Eurypterida from the Ordovician

and Silurian of New York: Journal of Paleontology, v. 36, p. 211–221.

Kluessendorf, J., 1994, Predictability of Silurian Fossil-Konservat-Lagerstätten in North

America: Lethaia, v. 27, p. 337–344.

Kues, B.S., and Kietzke, K.K., 1981, A large assemblage of a new eurypterid from the Red

Tanks Member, Madera Formation (Late Pennsylvanian–Early Permian) of New Mexico:

Journal of Paleontology, v. 55, p. 709–729.

Lamsdell, J., and Selden, P., 2013, Babes in the wood - a unique window into sea

ontogeny: BMC Evolutionary Biology, v. 13, p. 98.

Macleod, N., 1999, Generalizing and extending the eigenshape method of shape space

visualization and analysis: Paleobiology, v. 25, p. 107–138, doi: 10.2307/2665995.

Macleod, N., 2013, Going round the bend II: Extended eigenshape analyses: The Palaeontology

Newsletter, v. 81, p. 23–39.

Plotnick, R.E., 1983, Patterns in the evolution of the eurypterids: Unpublished Ph.D. thesis,

Unpublished Ph.D. dissertation, University of Chicago, University of Chicago, 411 p.

Rasband, W., 2011, ImageJ, Ver. 1.44, National Institutes of Health, Bethesda, Maryland,

http://imagej.nih.gov/ij/.

Rohlf, F.J., 2013, tpsDIG2, Ver. 2.17, SUNY, Stony Brook.

200

Scott, R.W., 1971, Eurypterid from the (Pennsylvanian and Permian),

Southwestern Pennsylvania: Journal of Paleontology, v. 45, p. 833-837.

Sheets, D.H., 2014a, IMP8, Canisius College, Buffalo.

Sheets, D.H., 2014b, Regress8, Canisius College, Buffalo.

Sheets, H.D., Kim, K., and Mitchell, C.E., 2004, A combined landmark and outline-based

approach to ontogenetic shape change in the Ordovician trilobite Triarthrus becki, in

Elewa, A.M.T., (ed.), Morphometrics: Applications in Biology and Paleontology:

Springer, New York, Berlin, p. 67-82.

Tetlie, O.E., Brandt, D.S., and Briggs, D.E.G., 2008, Ecdysis in sea scorpions (Chelicerata:

Eurypterida): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 265, p. 182–194,

doi: 10.1016/j.palaeo.2008.05.008.

Tetlie, O.E., Tollerton, V.P., Jr., and Ciurca, S.J., Jr., 2007, Eurypterus remipes and E. lacustris

(Chelicerata: Eurypterida) from the Silurian of North America: Bulletin of the Peabody

Museum of Natural History, v. 48, p. 139–152, doi: 10.3374/0079-

032x(2007)48[139:eraelc]2.0.co;2.

Tollerton, V.P., Jr., 1987, Distortion in eurypterids; criteria for recognition and its taxonomic

significance, Geological Society of America Abstracts with Programs, p. 63.

Tollerton, V.P., Jr., 1989, Morphology, Taxonomy, and Classification of the Order Eurypterida

Burmeister, 1843: Journal of Paleontology, v. 63, p. 642-657, doi: 10.2307/1305624.

201

Tollerton, V.P., Jr., 1992a, Heterochrony in eurypterids and the ontogenetic resolution of

morphological differences in Eurypterus remipes and E. lacustris, Geological Society of

America Abstracts with Programs, p. 98.

Tollerton, V.P., Jr., 1992b, Preliminary study of the shape of eurypterid prosomas using Fourier

analysis, North American Paleontological Convention: The Paleontological Society

Special Publications 6, p. 294.

Tollerton, V.P., Jr., 1993, Comparative ontogeny of Eurypterus remipes DeKay, 1825 and

Eurypterus lacustris Harlan, 1834: Unpublished M.S. thesis, Unpublished M.S., State

University of New York at Buffalo, New York, Buffalo, NY.

Vrazo, M.B., and Braddy, S.J., 2011, Testing the ‘mass-moult-mate’ hypothesis of eurypterid

palaeoecology: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 311, p. 63–73,

doi: 10.1016/j.palaeo.2011.07.031.

Vrazo, M.B., Hunda, B.R., and Brett, C.E., 2013, Semi-landmark analysis of eurypterids: a new

tool for assessing ecophenotypy: Geological Society of America Abstracts with

Programs, v. 45, p. 458

Webster, M., and Sheets, D.H., 2010, A practical introduction to landmark-based geometric

morphometrics, in Alroy, J., and Hunt, G., (eds.), Quantitative methods in paleobiology:

The Paleontological Society Papers, Volume 16, The Paleontological Society, p. 163-

188.

Witte, M., and Yacobucci, M.M., 2015, Morphometric analysis of the trilobite Eldredgeops rana

to assess geographic patterns of variation in the Michigan and Appalachian basins during

202

the Middle Devonian Period: Geological Society of America Abstracts with Programs, v.

47, p. 450

Zelditch, M.L., Swiderski, D.L., and Sheets, H.D., 2012a, Geometric Morphometrics for

Biologists : A Primer (2nd Edition): Academic Press, Saint Louis, MO, USA.

Zelditch, M.L., Swiderski, D.L., and Sheets, H.D., 2012b, A Practical Companion to Geometric

Morphometrics for Biologists: Running analyses in freely-available software: Elsevier

Academic Press. http://booksite.elsevier.com/9780123869036/content/Workbook.pdf.

203

FIGURES

FIGURE 1. Paleogeographic reconstruction of Laurentia and adjacent paleocontinents in the

Silurian. The Appalachian basin of Laurentia is identified by the oval. Modified from Blakey

(2013).

204

FIGURE 2. Eurypterus carapaces with differing carapace margin morphology. All scales in mm.

A) YPM #210626, with straight carapace margin. B) YPM #210341, embayment structure present, cf. Tetlie et al. (2007).

205

FIGURE 3. Regional map northern Appalachian basin and stratigraphic column of the upper

Silurian Bertie Group. Collection localities for specimens used in this study are starred. Silurian bedrock exposures are shaded in gray. The stratigraphic column on the left shows the upper

Silurian units exposed in the western part of the outcrop belt at Ridgemount Quarry, Ft. Erie,

Ontario, and environs; the column on the right shows upper Silurian units exposed to the east

206 near the distal end of the outcrop belt at Passage Gulf, NY. Stratigraphy following Vrazo et al.

(unpublished data; Chapter IV). Adapted from Edwards et al. (2004) and Tetlie et al. (2007).

207

FIGURE 4. Eurypterus carapace with first tergite attached (YPM #210341) depicted with linear measurements, landmarks, and semi-landmarks used in this study. Scale in mm. Horizontal and vertical lines represent carapace width and length measurements recorded, respectively. The orange dashed line represents the idealized 90° axis of the specimen. In this example, the true midline of the specimen (in black) is only offset from the idealized 90° axis by ~0.3°, and thus is considered suitable for subsequent landmark and semi-landmark analyses (see text for further details). Numbered large red circles represent fixed landmark positions recorded. Small red circles on yellow line represent semi-landmarks within the curve prior to replacement with helper points (see text for details). The start- and end-points of the semi-landmark curve are identical to landmarks #2 and #3, respectively, and will be removed prior to multivariate analyses.

208

Ellicott Creek Breccia Member (N = 424)

Density

Phelps Waterlime Member (N = 147)

Density

Length (mm)

FIGURE 5. Size-frequency distribution of all carapace lengths measured in this study.

Figure 7. Eurypterus from the Phelps Waterlime Member (blue squares, n = 101) overlain by

Eurypterus from the Ellicott Creek Breccia (red squares, n = 175) following Procrustes superimposition of landmark and semi-landmark data (left). The Procrustes mean of both populations is presented on the right.

209

A

B

FIGURE 6. Composites and mean shapes of the Phelps Waterlime (PWM) and Ellicott Creek

Breccia (ECB) samples following Procrustes superimposition. No scale. A) Separate composite

210 images of the PWM (left) and ECB (right) samples. Black circles represent fixed landmarks.

Blue squares represent semi-landmarks following reduction using helper points. Red squares represent helper points (presented only for visualization; helper points are not used in analyses), see text for details. B) Left: Overlapping composite images of the PWM (red) and ECB (blue) samples. Right: Overlapping Procrustes mean shapes of each sample.

211

Sample Variance

Landmark/Semi-landmark Number

FIGURE 7. Plot of jackknife of sample variance following removal of individual landmarks and

semi-landmarks. Samples are ordered from lowest to highest according to sample variance (y-

axis) when a landmark or semi-landmark is omitted (x-axis). Lower variance when a landmark or

semi-landmark is excluded indicates that to what extent that point contributes to total variance.

212

A

PC 2 PC

PC 1

Scree Plot as Percentage of Variance Scree Plot as Percentage of Variance Scree Plot as Percentage of Variance 0.2 0.2 0.2 B C D

0.15 0.15 0.15

0.1 0.1 0.1

0.05 0.05 0.05

0 0 0

-0.05 -0.05 -0.05

-0.1 -0.1 -0.1

-0.15 -0.15 -0.15

-0.2 -0.2 -0.2

-0.25

-0.25 -0.25

-0.4 -0.3 -0.2 -0.1 -0.40 0.1-0.3 0.2-0.2 0.3 -0.1 -0.4 0 -0.3 0.1 -0.2 0.2 -0.1 0.3 0 0.1 0.2 0.3 PC 1 PC 2 PC 3

FIGURE 8. Plot of scores for the first two PCs (A) and vector plots of variation along the first

three PCS (B–D) from a PCA of all specimens from the Phelps Waterlime Member (PWM, n =

213

101) and Ellicott Creek Breccia (ECB, n = 175) following Procrustes superimposition. B = PC 1;

C = PC 2; D = PC 3.

214

ProcrustesDistance

Log Centroid Size

FIGURE 9. Plot of Procrustes distance against Log Centroid size for Eurypterus cf. remipes from the Phelps Waterlime Member (PWM, n = 101) and Ellicott Creek Breccia (ECB, n = 175) following Procrustes superimposition. Correlation coefficients: PWM, r = 0.83, p < 0.001; ECB, r = 0.6, p < 0.001. Procrustes distance and Log Centroid size calculated from following

Procrustes superimposition of landmarks and semi-landmark data.

215

0.2 A

0.15

0.2

0.1

0.05 0.1

0

0

-0.05

-0.1

-0.1

-0.15

-0.2 -0.2

-0.25

-0.3 -0.5 -0.4 -0.3 -0.2 -0.1 0 -0.5 0.1-0.4 -0.3 0.2 -0.2 0.3 -0.1 0 0.1 0.2 0.3 0.4

0.2 B 0.3

0.15

0.2

0.1

0.05 0.1

0

0

-0.05

-0.1

-0.1

-0.15

-0.2 -0.2

-0.25

-0.3

-0.5 -0.4 -0.3 -0.2 -0.1 -0.6 0 0.1 -0.4 0.2 -0.20.3 0 0.2 0.4 FIGURE 10. Plots of ontogeny-related shape variation when Phelps Waterlime Member (A) and

Ellicott Creek Breccia (B) samples are regressed on the three smallest specimens. Vector plot

(left); thin-plate spline deformation plot (right).

216

A

PC2

PC 1

0.2 B 0.2 C 0.2 D

0.15 0.15 0.15

0.1 0.1 0.1

0.05 0.05 0.05

0 0 0

-0.05 -0.05 -0.05

-0.1 -0.1 -0.1

-0.15 -0.15 -0.15

-0.2 -0.2 -0.2

-0.25 -0.25 -0.25

-0.4 -0.3 -0.2 -0.1 -0.4 0 -0.3 0.1 -0.2 0.2 -0.1 -0.40.3 0 -0.3 0.1 -0.2 0.2 -0.1 0.3 0 0.1 0.2 0.3

PC 1 PC 2 PC 3

FIGURE 11. Plot of scores of the first two PCs (A), and vector plot of variation along the first

three PCs (B–D), from a PCA of size-standardized (largest) specimens from the Phelps

217

Waterlime Member (n = 101) and Ellicott Creek Breccia (n = 175) following size- standardization. B = PC 1; C = PC 2, D = PC 3.

218

A

PC2

PC 1

0.2 0.2 B 0.2 C D

0.15 0.15 0.15

0.1 0.1 0.1

0.05 0.05 0.05

0 0 0

-0.05 -0.05 -0.05

-0.1 -0.1 -0.1

-0.15 -0.15 -0.15

-0.2 -0.2 -0.2

-0.25 -0.25 -0.25

-0.3 -0.4 -0.3 -0.2 -0.1 -0.4 0 -0.3 0.1 -0.2 0.2 -0.1 -0.4 0.3 0 -0.3 0.1 -0.2 0.2 -0.1 0.3 0 0.1 0.2 0.3

PC 1 PC 2 PC 3

219

FIGURE 12. Plot of scores (A) of the first two PCs, and vector plot of variation along the first three PCs (B–D), from a PCA of size-standardized (largest) specimens from the Phelps

Waterlime Member (n = 101). B = PC 1; C = PC 2, D = PC 3.

220

A

PC2

PC 1

0.2 B 0.2 C 0.2 D

0.15 0.15 0.15

0.1 0.1 0.1

0.05 0.05 0.05

0 0 0

-0.05 -0.05 -0.05

-0.1 -0.1 -0.1

-0.15 -0.15 -0.15

-0.2 -0.2 -0.2

-0.25 -0.25 -0.25

-0.4 -0.3 -0.2 -0.1 -0.4 0 -0.3 0.1 -0.2 0.2 -0.1 -0.40.3 0 -0.3 0.1 -0.2 0.2 -0.1 0.3 0 0.1 0.2 0.3

PC 1 PC 2 PC 3

FIGURE 13. Plot of scores (A) of the first two PCs, and vector plot of variation along the first

three PCs (B–D), from a PCA of size-standardized (largest) specimens from the Ellicott Creek

Breccia (n = 175). B = PC 1; C = PC 2, D = PC 3.

221

FIGURE 14. Procrustes mean shapes (size-standardized) of Ellicott Creek Breccia specimens with (red circles) and without (black crosses) an embayment structure (sensu Tetlie et al., 2007)

(n = 175). No scale.

222

FIGURE 15. Plot of overlapping Procrustes means from sub-samples of specimens from the

Phelps Waterlime Member (red triangles; n = 83) and Ellicott Creek Breccia (black stars; n = 60) that bear an embayment structure (sensu Tetlie et al., 2007). No scale.

223

A

PC2

PC 1

0.2 B C 0.2 D

0.15 0.15 0.15

0.1 0.1 0.1

0.05 0.05 0.05

0 0 0

-0.05 -0.05 -0.05

-0.1 -0.1 -0.1

-0.15 -0.15 -0.15

-0.2 -0.2 -0.2

-0.25 -0.25

-0.25

-0.3 -0.5 -0.4 -0.3 -0.2 -0.5 -0.1 -0.4 0 -0.3 0.1 -0.2 0.2 -0.5 -0.1 0.3 -0.4 0 0.4 -0.3 0.1 -0.2 0.2 -0.1 0.3 0 0.4 0.1 0.2 0.3 0.4 0.5

PC PC PC

1 2 3

224

FIGURE 16. Plot of scores (A) and vector plots of variation along the first two PCs (B, C) from a PCA of size-standardized (largest) Eurypterus carapaces bearing embayment structures (sensu

Tetlie et al., 2007) from the Phelps Waterlime (n = 83) and Ellicott Creek Breccia (n = 60) members. B = PC 1; C = PC 2.

225

A

CV 2

CV 1

0.2 B C

0.15 0.15

0.1 0.1

0.05 0.05

0 0

-0.05 -0.05

-0.1 -0.1

-0.15 -0.15

-0.2 -0.2

-0.25

-0.25

-0.3 -0.4 -0.3 -0.2 -0.1 -0.40 0.1-0.3 0.2-0.2 0.3 -0.1 0 0.1 0.2 0.3

CV 1 CV 2

226

FIGURE 17. Plot of scores from a CVA (A) and vector plots of variation along the first two CVs

(B, C) from a CVA of Eurypterus carapaces bearing embayment structures (cf. Tetlie et al.,

2007) from the Phelps Waterlime (n = 83) and Ellicott Creek Breccia (n = 60) members. B = CV

1; C = CV 2.

227

TABLE 1. Summary statistics for specimens from the Phelps Waterlime Member (PWM),

Ellicott Creek Breccia (ECB), and two error test specimens following Procrustes

Superimposition of landmarks and semi-landmarks (following reduction). Test A carapace length

= 5 mm; Test B carapace length = 26 mm.

PWM ECB Test A Test B (n = 101) (n = 175) (n = 10) (n = 10) Mean Centroid Size 6.39933 3.61614 7.82867 1.43734 Std. deviation CS 2.25806 1.64967 NA NA Max CS 12.6078 13.6978 NA NA Min CS 2.674300 0.882265 NA NA Variance (SS distances/(n-1)) : 0.001011 0.001703 0.000027 0.000039 Variance, 0.025% (1600 bootstraps) 0.000885 0.001547 0.000018 0.000022 Variance, 0.975% (1600) 0.001120 0.001856 0.000030 0.000050 RMS scatter about mean : 0.031800 0.041267 0.005165 0.006254 Standard Error for the disparity 0.000061 0.000077 NA NA

228

TABLE 2. Summary variance statistics for the sub-samples of specimens bearing an embayment structure from the Phelps Waterlime Member and Ellicott Creek Breccia.

PWM ECB (n = 83) (n = 60) Variance (SS distances/(n-1)) : 0.000648125 0.00079764 Variance, 0.025% (1600 0.00054709 0.00063461 bootstraps) Variance, 0.975% (1600 0.00072543 0.00097343 bootstraps) RMS scatter about mean : 0.0254583 0.0282425 Standard Error for the disparity 0.00004496 0.00008742

229

TABLE 3. Results of jackknife grouping test based on distance-based CVA (see Fig. 16). See text for discussion.

ECB PWM ECB 46 14 PWM 16 67

230

Chapter VI

CONCLUSIONS

Eurypterid paleoecological research has long been impeded by a lack of stratigraphic detail at both the bed-level and at the regional scale. The research undertaken for this dissertation represents the first attempt to consolidate regional eurypterid occurrence data within a high- resolution stratigraphic framework. The results indicate that re-evaluation of the sites in which eurypterids are already known to occur can proffer new insights into these enigmatic organisms.

Inasmuch as analysis of eurypterid occurrences at the bed-level can further our understanding of their paleoecology, consideration of their evolution within a stratigraphic framework is also important, particularly given the growing body of evidence that supports a relationship between environment, preservation, and origination/extinction (e.g., stratigraphic paleobiology).

The following conclusions are made from this dissertation research:

1) Eurypterids are more common in the central Appalachian basin than was previously

thought. However, their appearance only within certain stratigraphic positions and

facies suggests that they were largely ephemeral communities that were influenced by

shifting salinity levels across the basin.

2) Eurypterids most likely did not inhabit briny (i.e., 350 ppt) conditions that led to salt

hopper formation. It is concievable that eurypterids could tolerate mild hypersalinity

(similar to modern xiphosurans), but it seems unlikely that they inhabited

environments with salinities significantly greater than normal marine (euhaline; ~35

ppt). If we conclude that eurypterids were not halotolerant organisms, and that they

were normally restricted to normal marine eu- or hyposaline settings, this places a

constraint on their salinity tolerance. This constraint can then be used to better

231

understand the role of environment in their transition to freshwater, and/or their

extinction in marine settings.

3) Eurypterid occurrences in the Appalachian basin appear to be the result of both biotic

(ecological preferences) and abiotic controls (i.e., anoxia/hypersalinity) on

preservation. These conditions occur in situ, within the facies successions in

nearshore settings in the Appalachian basin during the Mid-Paleozoic, allowing

occurrences of eurypterid remains to be predicted within a sequence stratigraphic

framework, both in North America, and elsewhere.

4) The general paucity of eurypterid remains in the fossil record necessitates the use of

isolated parts such as carapaces for systematic identification. However, the results of

the landmark/semi-landmark analysis indicate that caution must be exercised in order

to avoid oversplitting when using relatively featureless parts that lack homologous

(Type 1) features. Conservatively, eurypterid carapaces should only be used to

identify specimens to the genus level. If taxa are well-defined, however, an integrated

landmark/semi-landmark approach can offer insight into phenotypic variation over

regional, and potentially temporal scales.

232

APPENDIX

Chapter II Supplementary Materials

APPENDIX FIGURE 1. Field photographs showing key stratigraphic and sedimentological features of the Winfield Quarry eurypterid fossil locality. Note 10-cm long photo scale in all photos except A, X (no scale), B, C, E (camera lens cap), H (person), and W (hammer). A) Well- exposed dip slopes of uppermost Tonoloway Formation exposed in Winfield Quarry. Rectangle marks location of measured section in Figure 5A. (E) marks area where nearly all eurypterid

233 fossils were recovered. View toward the east. B) Calcite-replaced evaporitic? vugs in micrite ~30 cm below the base of measured section. C) Laminated micrite, including possible microbial laminae. D) Micrite and wackestone with desiccation cracks (=D) and thrombolites (=T) ~20–55 cm above base of measured section. Scale bar in rectangle. E) Desiccation cracks ~20 cm above base of measured section. F) Leperditicopids ~25 cm above base of measured section. G) Mud- draped thrombolites ~40 cm above base of measured section. H) Thinly laminated calcareous shale (=L) overlain by coarser-grained carbonate strata, chiefly packstone with subordinate grainstone and rudstone (=P). I) Laminae in eurypterid-bearing calcareous shale ~70 cm above base of section. J) Low-amplitude, straight-crested ripples ~75 cm above base of measured section. K) Abundant leperditicopid fossils in thinly laminated calcareous shale (left) overlain by eurypterid-bearing shale with fewer leperditicopid fossils (right). L) Close-up of leperditicopid fossils in left side of K. M) Abundant leperditicopid fossils in thinly laminated calcareous shale.

N–O) Thinly laminated calcareous shale with disarticulated eurypterid remains ~80 cm above base of measured section: isolated prosoma in rectangle in upper left of N; isolated tergite in rectangle in right center of O. P) Interbedded wackestone and packstone ~130 cm above base of measured section. Q) Grainstone and wackestone ~140 cm above base of measured section. R)

Grainstone ~755 cm above base of measured section. S) Rudstone/grainstone with outsized micritic intraclasts ~760 cm above base of measured section. T) Fragmented cladopora? fossils

~770 cm above base of measured section. U) Low-amplitude, straight-crested ripples in wackestone/packstone ~575 cm above base of measured section. V) Wackestone with leperditicopid fossils ~860 cm above base of measured section. W–X) Open-marine fossils typical of the overlying Keyser Formation at the study site, including stromatopora (W) and disarticulated crinoids (X).

234

APPENDIX TABLE 1. Additional localities with exposures of the Tonoloway Formation scouted during this study.

235

Entirely reclaimed. reclaimed. Entirely

Highly overgrown Highly

township building township

driveway for the the for driveway

Filled in as a of part in Filled

28).

by Inners (1997, p. p. (1997, Inners by

to as to “J.R.M.” Road

Incorrectly referred Incorrectly

Highly overgrown Highly

Notes

, p. 28 p. ,

Inners, 1997, p. 28 p. 1997, Inners,

Inners, 1997 Inners,

Inners, 1997 Inners,

1986, p. 166 - 169 166 p. 1986,

Cotter and Inners, Inners, and Cotter

Schuchert, 1903 Schuchert,

Reference

2.9 km west of village of Paxtonville of west village of km 2.9

1.14 km east of Grovania, Pa. east Grovania, of km 1.14

Intersection of Rt. 22 and Rt. 522, nr. Mt. Union, Pa. Union, Mt. nr. Rt. 522, and Rt. 22 of Intersection

1.2 km south of Mandata, Pa. Mandata, of south km 1.2

2.7 km west of village of Mifflinburg, Pa. Mifflinburg, of west village of km 2.7

0.3 km south of village of Washingtonville, Pa. Washingtonville, of village of south km 0.3

5 km west of Allenwood, Pa. west Allenwood, of km 5

1.2 km southwest of Turbotville, Pa. Turbotville, of southwest km 1.2

0.5 km west of Atkinson Mills, Pa. Mills, west Atkinson of km 0.5

2.1 km southwest of Lewisburg, Pa. Lewisburg, of southwest km 2.1

4.96 km southwest of Washingtonville, Pa. Washingtonville, of southwest km 4.96

Milton, Pa. Milton,

0.1 km west of intersection of Rt. 642 and Rt. 147, Rt. 147, and Rt. 642 of west intersection of km 0.1

On Rt. 103, 4.4 km east of Kistler, Pa. east Kistler, of km 4.4 Rt. On 103,

Selinsgrove Junction, Pa. Junction, Selinsgrove

Southeast side of rail tracks along Susquehanna River, River, Susquehanna tracks along rail of side Southeast

Nearest town

40°45'59.41"N/77° 6'47.18"W 40°45'59.41"N/77°

40°58'41.56"N/76°30'45.42"W

40°23'38.82"N/77°52'19.72"W

40°40'29.54"N/76°49'59.63"W

40°54'8.37"N/77°4'58.45"W

41°2'56.92"N/76°40'29.23"W

41°7'20.41"N/ 76°57'17.56"W 41°7'20.41"N/

41°5'39.89"N/76°46'53.08"W

40°27'13.58"N/77°49'33.72"W

41° 0'20.51"N/76°53'13.65"W 41°

41°1'55.76"N/76°43'40.27"W

41°0'27.31"N/76°49'41.38"W

40°21'37.43"N/77°49'27.30"W

40°49'8.96"N/76°49'42.36"W

GPS data GPS

Paxtonville Quarry Paxtonville

Grovania Quarry Grovania

Mt. Union outcrop Union Mt.

Meckley's Quarry Meckley's

Iddings Quarry Iddings

Washingtonville

Allenwood Prison Quarry Prison Allenwood

Moser Quarry Moser

Atkinson Mills Atkinson

J.P.M. Quarry Road

Milton Quarry Milton

East Milton

Allenport roadcut Allenport Selinsgrove Junction Selinsgrove Locality name Locality

236

Chapter III Supplementary Materials

237

APPENDIX FIGURE 1. Google Earth .kmz file containing locality and stratigraphic data for all eurypterid-salt hopper-bearing intervals.

238

Chapter V Supplementary Materials

APPENDIX TABLE 1 Univariate measurements for all Eurypterus from the Phelps Waterlime Member (Fiddlers Green Formation, Bertie Group), Passage Gulf., NY, and Ellicott Creek Breccia (Fiddlers Green Formation, Bertie Group), Ridgemount Quarry, ON. “CP” = counterpart.

Phelps Waterlime Member

Used for Carapace Carapace Embayment LM/SLM Midline Width Length Specimen ID (YPM #) visible analysis offset (°) (mm) (mm) 210163 y * 90.23 16.00 12.64 210168 n * 89.77 43.53 33.44 210170 y * 90.43 17.03 12.43 210175 90.60 38.60 29.68 210178 13.03 210181 90.46 32.32 23.51 210188 y * 90.79 34.95 25.47 210196 y * 89.21 26.23 19.12 210214 89.01 13.12 210232 y * 19.84 19.75 13.65 210233 y * 89.34 21.00 15.18 210235_large y * 90.91 29.28 23.01 210235_small 89.92 12.15 8.83 210239 n * 90.43 20.33 15.72 21023X 90.31 11.73 8.66 210243 n * 88.38 20.24 210252 85.73 43.73 27.85 210257 y * 89.06 27.38 20.10 210262 88.70 39.18 28.92 210265_CP y * 89.97 34.68 24.84 210268 92.23 23.04 16.58 210277 y * 38.93 210281 90.11 26.15 20.95 210283 n * 90.00 26.97 19.54 210297 n * 90.10 32.65 21.76 210300 91.47 14.42 10.37 210304 y * 90.43 48.77 36.55 210305 y * 90.85 28.12 19.64 210306 y * 90.47 19.98 15.01 210307 y * 89.60 21.56

239

210308 y * 89.58 34.57 26.05 210310 90.72 28.45 20.36 210319 y * 90.11 21.94 17.22 210320 y * 89.79 30.82 22.13 210325 y * 90.69 34.08 25.85 210328 n * 88.55 26.25 17.95 210329 53.75 37.56 210336 y * 89.94 28.82 20.28 210341 y * 89.36 35.15 25.68 210342 y * 91.37 24.44 18.02 210346 88.07 28.43 21.73 210349 y * 89.61 21.12 15.69 210351 y * 89.59 15.92 11.60 210354 y * 88.96 18.44 13.34 210355 y * 90.86 22.70 17.13 210359 y * 89.63 25.46 19.17 210368 y * 90.51 23.71 18.31 210371 y * 91.32 37.21 26.50 210372 y * 90.49 29.13 21.13 210375 y * 89.15 31.01 22.62 210376 y * 88.93 24.20 18.00 210378 n * 91.29 21.68 15.20 210379 88.87 13.63 10.07 210380 n * 91.29 24.12 16.06 210389 y * 90.34 62.11 43.46 210394 y * 90.29 16.56 12.43 210397 y * 90.28 54.43 38.89 210398? n * 91.38 19.60 13.98 210399 90.12 14.10 10.56 210409 y * 88.90 45.32 32.15 210411_specimen 1 y * 90.06 24.66 18.89 210411_specimen 2 y * 91.15 29.71 21.34 210430 y * 90.19 19.98 14.92 210436 89.70 35.51 27.56 210449 y * 90.38 52.01 40.10 210457 89.93 34.50 24.46 210458 y * 88.51 21.68 15.28 210474 92.55 55.85 40.63 210478 y * 88.75 18.15 13.25 210483 y * 88.87 22.50 16.28 210486 y * 91.46 27.65 19.94 210489 y * 90.59 31.73 24.70 210491 y * 89.01 37.27 26.31

240

210496 n * 89.61 30.53 21.00 210501 89.24 33.18 23.35 210513_specimen 1 y * 89.28 26.84 20.07 210513_specimen 2 90.76 14.28 10.72 210514 88.20 10.03 7.59 210519 n * 90.16 25.65 17.01 210522 y * 90.40 18.52 13.48 210531_CP y * 90.36 25.25 18.68 210532 y * 89.78 28.45 20.34 210532 (wrong ID) y * 89.14 26.29 17.59 210545 y * 90.50 30.20 22.33 210561 y * 90.03 15.51 11.63 210562 y * 88.47 51.86 35.52 210567 y * 90.05 48.66 35.17 210568 y * 88.40 24.33 16.94 210569 y * 91.01 14.42 210579 89.80 20.19 210584 y * 88.81 25.54 18.98 210588 y * 91.41 40.75 27.96 210589 y * 90.85 19.41 14.22 210592_specimen 1 13.17 9.59 210592_specimen 2 10.25 7.27 210595 91.22 30.45 21.30 210597 92.03 24.80 17.08 210598 y * 90.55 37.71 25.93 210602 88.63 10.06 7.92 210603 y * 89.64 38.72 26.99 210613 26.40 20.17 210626_CP n * 89.30 28.27 20.19 210811 y * 89.74 29.47 21.24 210813 92.03 17.67 13.49 210819 87.20 60.19 39.79 210821 y * 90.21 21.22 15.53 210839 15.01 210851 n * 90.38 37.16 24.43 210856 y * 90.23 25.45 18.08 210857? y * 89.84 24.50 17.99 210862 89.26 26.61 19.29 211552 89.44 32.64 24.41 211206 y * 91.07 34.52 25.25 211207 87.01 52.37 34.15 211210 92.80 44.35 34.57 211211 88.34 31.75

241

211213 y * 89.45 26.65 19.80 211214 y * 89.06 30.68 211215 y * 89.95 22.49 211216 y * 91.74 44.35 31.13 211219 y * 90.07 35.46 24.90 211220 y * 88.85 19.27 13.92 211223_CP y * 88.55 17.76 13.58 211232 y * 89.60 59.85 42.20 211242 y * 89.11 42.06 211256 89.52 18.94 14.46 211265 90.23 30.36 21.91 211268 y * 90.00 32.87 24.29 211278 88.43 32.00 22.97 211283 y * 90.22 47.02 34.44 211286 y * 90.78 31.38 23.01 211316 y * 89.97 22.54 16.95 211408 y * 90.76 21.08 16.13 211541 y * 90.72 33.11 25.27 211551 n * 91.02 16.16 11.61 211552 y * 90.02 32.64 23.19 211675 y * 88.83 22.43 16.16 211875 89.96 42.67 29.61 211876 y * 90.60 29.93 22.44 219378 91.26 21.54 15.11 222343 y * 90.48 36.99 27.94 222370 n * 91.64 41.21 27.29 222378 n * 89.45 13.65 9.47 222385 21.02 222386 89.98 32.46 23.57

242

Ellicott Creek Breccia Used for Carapace Carapace Embayment LM/SLM Midline Width Length Specimen ID (YPM #) visible analysis offset (°) (mm) (mm) 210870_CP y * 90 50.33 38.29 210871 30 23.34 210874 y * 91.23 13.7 10.34 210875 n * 13.18 10.12 210877_CP n * 89.78 19.55 15.36 210878 9.77 7.10 210882 y * 90.63 22.34 17.98 210883_specimen 1 10.77 6.89 210883_specimen 2 17.15 12.32 210892 9.52 6.87 210898 n * 89.23 16.92 12.40 210900 n * 90.45 6.67 4.93 210903 18.50 13 210904 9.02 6.38 210905 n * 91.07 13.78 8.66 210906 12.91 9.63 210908 13 9.7 210911 12.72 9.48 210912 7.09 4.91 210913 7.7 5.13 210915 16.94 12.90 210916 n * 90.09 17.78 11.64 210917 23.23 15.67 210920 19.36 12.90 210921 n * 89.88 16.52 12 210932 18.01 13.66 210935 19.66 15.82 210942 22.06 17.31 210949 18.02 13.64 210951 88.34 18.06 14.34 210952 10.8 8.14 210978 8.76 6.40 210979_CP y * 88.76 16.47 12.79 210982_CP y * 90.69 15.36 12.17 210983_CP 21.59 16.39 210988_CP y * 89.3 17.70 14.00 210991 11.2 7.88 210996 16.57

243

210998 6.22 5.00 211001 4.19 3.00 211002 18.03 211010 12.54 8.41 211011 9.28 7.15 211012 21.06 15.99 211014 25.5 19.93 211019 n * 20.94 15.80 211020 16.11 12.24 211021 24.52 18.82 211038 n * 90.14 13.58 11.03 211039 6.59 211041 11.66 8.94 211043 y * 90.49 22.32 18.89 211044 8.45 6.05 211045 n * 89.18 18.08 12.71 211050 n * 90.27 14.57 11.21 211051 n * 89.7 10.21 6.76 211054 n * 14.65 10.38 211055 y * 23.25 17.28 211056 n * 90.74 14.08 9.81 211057 10.07 211060 9.5 6.57 211061 17.87 11.11 211062 87.08 22.40 14.59 211063 n * 90.47 15.97 12.84 211068 n * 91.21 17.31 12.19 211071 13.11 9.18 211072 n * 90.66 11.35 7.99 211073 n * 89.39 15.18 10.17 211074 n * 90.47 23.84 16.88 211075 13.61 11.06 211076 y * 89.04 19.1 14.05 211077 n * 90.34 14.85 11.05 211078 y * 89.92 18.5 14.05 211079 n * 90.92 17.45 11.82 211080 y * 90 11.66 8.06 211081 23.53 16.94 211082 92.33 23.2 15.93 211083 5.36 4.12 211085 y * 90.37 16.82 11.85 211086 10.19 6.27 211087 n * 88.85 21.53 15.98

244

211089 n * 89.52 11.18 7.47 211090 n * 22.2 14.90 211094 y * 90.44 19.47 15.30 211099 y * 89.89 16.5 12.27 211104 12.81 211105 11.10 7.68 211106 n * 89.48 18.75 12.81 211107 18.64 12.02 211108 22.28 16.58 211109 14.78 10.82 211111 n * 9.37 6.45 211115 y * 89.72 16.17 12.55 211116 5.59 211117 15.32 10.18 211118 y * 90.34 18.4 13.95 211119 13.77 211120 n * 89.44 17.15 12.05 211121 24.08 16.21 211122 22.65 16.82 211124 y * 89.9 16.66 14.21 211125 n * 90 16 13.12 211126 n * 89.38 14.17 10.53 211128 88.32 13.79 9.78 211129 8.87 211130 n * 91.29 12.69 8.86 211131 12.62 211132 18.12 13.64 211133 14.79 211134 n * 90.43 24.1 17.31 211135 12.40 211137 9.18 6.05 211138 8.82 6.89 211139 9.81 6.35 211140 n * 19.90 13.05 211141 12.53 211142 90 10.72 7.16 211144 (incorrect ID) 8.52 6.01 211145_CP n * 23.69 17.14 211148 20.08 15.04 211149 19.5 15.57 211150 21.51 14.99 211153 n * 89.5 10.79 7.62 211163_CP n * 90 10.80 7.56

245

211164 n * 90.56 18.56 13.00 211166 n * 90 9.9 6.95 211167_CP y * 89.62 21.42 16.66 211168 n * 18.99 211176 20.61 211185 n * 89.74 16.06 12.01 211188 n * 91.45 17.82 14.46 211192 9.81 7.01 211193 88.78 26.44 18.83 211194 n * 89.38 19.56 13.36 211197 7.93 6.17 211194 n * 89.93 19.56 13.36 211198 n * 89.75 11.62 8.19 211199 13.75 211202 9.23 6.31 212051_CP n * 89.6 46.88 33.95 212056 n * 88.9 22.55 16.67 212063 14.19 11.51 212065 y * 16.43 12.84 212067 n * 89.39 12.09 8.09 212068 6.78 5.13 212070 87.88 29.46 19.48 212073 y * 90.66 10.22 7.65 212076 n * 89.77 7.33 5.00 212079 n * 89.12 17.86 12.56 212080 21.22 15.72 212081 y * 17.18 12.46 212086 n * 89.8 16.55 11.35 212089 n * 21.64 16.65 212090 3.92 3.29 212093 n * 19.73 212094 n * 90.1 19.23 13.94 212096 y * 90.23 17.2 13.51 212097 n * 89.2 10.99 8.29 212099 23.417 16.00 212100 21.84 14.30 212102 y * 21.78 16.32 212103 y * 91.36 19.47 15.24 212104 y * 90.25 19.95 15.68 212111 n * 90.42 7.86 5.61 212113 y * 90.85 20.05 15.73 212115 12.47 212116 n * 90.14 20 14.49

246

212121 88.11 17.05 12.68 212123 n * 90.8 8.88 5.66 212124 n * 90.07 25.12 17.59 212125 n * 90 14.85 10.58 212129 n * 89.9 15.38 11.12 212130 n * 90 15.64 11.22 212131 18.97 212132_specimen 1 13.88 10.2 212132_specimen 2 23.78 16.32 212134 23.2 15.63 212135 y * 89.25 9 7.05 212136 n * 90.94 6.79 4.40 212137 90.86 21.76 15.36 212139 n * 89.86 15.5 11.36 212140 90.4 20.51 15.33 212141 n * 88.69 24.12 15.68 212143 18.49 212144 n * 90 20.85 15.13 212145 88.64 23.58 17.00 212148 18.89 212148_CP 18.89 212150 5.82 212151 19.79 15.43 212154 n * 13.83 212236 15.91 11.65 212237 13.91 212239 9.93 6.22 212246 n * 90 10.705 7.45 212248 91.74 11.96 8.64 212249 9.13 212250 7.91 212252 11.96 8.83 212253 22.5 14.80 212258 13.84 11.16 212260 y * 90.1 15.19 11.91 212261 89.07 16.09 12.69 212262 91.55 22.19 17.45 212266 96.64 17.96 14.44 212270 y * 90 23.65 19.08 212331 18.47 212333 y * 32.88 212411 88.32 13.97 10.67 212412 92.29 17.73 11.67

247

213259 13.21 213260 13.48 10.20 213954 17.93 13.18 213955 23.03 17.64 213958 24.22 19.17 213961_CP_large 21.21 15.38 213962 20.06 15.32 213965 10.52 213968 13.84 213971 13.54 11.06 214432 n * 90.21 11.98 8.74 214435 n * 89.04 11.15 8.44 214437 53.39 38.92 214438 20.18 15.97 214439 9.26 7.27 214440 y * 21.97 214443 89.22 8.30 5.96 214445 13.35 214448 y * 89.84 26.14 20.20 214451 n * 88.87 14.00 9.57 214452 y * 88.51 20.10 15.39 214453 26.01 18.29 214455 n * 89.58 11.34 8.29 214457 y * 90.48 6.97 5.47 214458 n * 89.45 14.56 9.79 214459 21.44 16.77 214461 14.51 214462 6.24 4.60 214464 89.79 16.05 11.87 214944 56.65 214945 24.17 19.77 214946 16.91 12.60 214948 19.78 14.35 214950 92.45 20.50 15.89 214955 12.43 214958x 7.91 214964 15.56 11.84 214969 7.4 5.96 214971 88.61 16.72 10.86 214973 15.6 10.67 214974 17.63 12.78 214976 14.44 10.35 214981 18.46 14.19

248

214982 20.08 14.49 214984 6.14 214985 n * 90 20.59 15.20 214987 18.64 12.65 214988 y * 22.09 16.34 214990 18.67 13.44 214991 18.29 13.91 214993 y * 17.74 14.14 214999 89.19 53.7 33.89 215028 31.82 215082 n * 89.87 13.81 9.76 217508_specimen 1 y * 90.25 11.80 8.88 217508_specimen 2 91.98 26.01 19.21 217509 13.49 217512 26 18.99 217513 y * 90.57 24.36 19.05 217516 18.29 12.81 217518 n * 88.62 21.73 16.87 217519 n * 90 6.44 4.54 217520 y * 90 8.84 6.87 217521 11.30 217522 n * 90.25 17.45 13.22 217523 89.09 21.50 12.90 217524 y * 91.38 25.43 18.63 217525 91.24 22.04 16.92 217527 y * 90 8.91 6.78 217528 90 9.52 6.63 217529 n * 91.16 10.86 7.15 217530 13.79 10.00 217531_CP n * 90.76 15.07 10.34 217532 15.68 10.82 217533 y * 88.93 14.08 11.36 217534 16.78 11.35 217535 17.18 14.46 217536 6.77 5.24 217537 y * 89.59 21.07 16.43 217540 58.49 45.21 217541 n * 90.19 23.51 16.65 217542 18.91 12.41 217544 n * 89.57 15.66 10.6 217545 y * 89.28 7.40 5.88 217546 n * 88.59 16.52 12.19 217547 n * 90 9.29 6.17

249

217548 n * 89.9 17.66 11.37 217549 y * 19.56 14.79 217550 n * 89.72 18.75 12.37 217552 y * 89.96 63.59 45.20 217553 23.04 18.33 217554 14.97 217556 17.8 11.8 217557 17.07 12.86 217559 y * 90.86 16.32 12.93 217561 n * 89.83 11.00 7.44 217564 5.62 4.00 217565 n * 90.24 16.84 12.11 217566 10.77 217569 y * 89.58 23.04 17.80 217571 10.3 7.79 217572 y * 90.84 16.36 13.02 217574 80.03 6.48 4.56 217576 12.78 9.52 217577 11.04 8.25 217579 20.33 13.99 217580 13.37 9.36 217582 3.84 2.97 217583 n * 90 8.94 6.12 217585 n * 89.75 15.68 10.44 217586 n * 90 15.38 10.47 217587 86.86 22.7 15.31 217589 87.34 18.97 14.65 217590 18.06 14.72 217591 91.34 23.27 17.58 217592 y * 89.58 17.42 12.45 217593 88.22 18.52 14.11 217594 90.51 16.92 11.56 217596_CP n * 90 3.685 3.11 217598 y * 90.09 20.06 14.90 2176__ 7.11 217601 n * 89.88 18.44 12.36 217602 n * 89.63 11.33 7.49 217603 87.92 21.14 15.18 217604 y * 89.44 15.04 11.92 217605 15.23 12.59 217606 92.48 7.79 5.08 217607 91.81 7.98 5.43 217608 n * 88.8 5.97 4.60

250

217609 y * 89.52 13.71 10.48 217610 88.74 12.66 8.70 217611 89.27 5.13 217612 n * 89.29 17.67 11.96 217613 n * 91.37 5.96 4.63 217614 n * 89.56 9.46 6.90 217615 91.93 9.15 6.51 217619 87.22 21.30 13.67 217623 n * 89.79 19.17 12.08 217625 19.82 14.42 217626 31.64 21.10 217627 y * 90.69 19.9 14.73 217628 88.72 18.79 13.02 217629 13.57 9.84 217630 22.47 14.43 217631 11.7 7.92 217633 15.34 12.03 217634 10.13 8.04 217635 12.74 9.26 217637 6.25 4.82 217638 9.42 7.66 217640 11.59 8.61 217641 n * 22.48 16.67 217644 25.87 217645 25.44 18.87 217646 88.84 21.01 15.36 217647 n * 90.33 5.97 4.40 217648 n * 90.15 11.7 7.84 217649 n * 91.43 12.34 8.90 217650 n * 89.54 12.24 8.40 217651 n * 90 6.14 4.33 217652 n * 90.18 8.7 6.90 217654 n * 90.11 15.21 11.25 217655 n * 10.86 7.00 217658_CP n * 90.85 16.96 11.38 21766X 90.47 5.87 4.58 217661 17.62 11.59 217662 16.56 11.91 217663 (217662_CP?) 16.15 11.70 217665 y * 16.29 12.70 217666 10.4 8.09 217667 n * 90.63 13.04 9.71

251

217668 n * 91.14 9.04 6.50 217669 6.91 217670 90.42 6.82 5.10 217671 20.52 13.38 217672 n * 90 8.39 6.03 217676 n * 89.38 12.6 9.09 217678 n * 18.28 12.34 217679 n * 90 9.8 6.26 217680 y * 90.24 6.59 5.03 217681 91.06 15.4 11.99 217683 n * 90.74 23.75 17.40 217684 8.38 5.75 217685 17.35 12.42 217686 90.65 12.03 217687 y * 89.63 13.17 10.24 288012 y * 89.64 22.53 18.01 75110202 90.83 22.2 16.68 unknownA y * 88.88 18.05 13.83 unknownB y * 89.3 23.09 18.64 unknownA 11.48 unknownB n * 88.87 23.74 16.91

252