GIS Based Biogeography of Cincinnatian (Upper Ordovician) Brachiopods with Special
Reference to Hebertella
A thesis presented to
the faculty of
the College of Arts and Sciences of Ohio University
In partial fulfillment
of the requirements for the degree
Master of Science
Brandon C. Klingensmith
August 2011
© 2011 Brandon C. Klingensmith. All Rights Reserved 2 This thesis titled
GIS Based Biogeography of Cincinnatian (Upper Ordovician) Brachiopods with Special
Reference to Hebertella
by
BRANDON C. KLINGENSMITH
has been approved for
the Department of Geological Sciences
and the College of Arts and Sciences by
Alycia L. Stigall
Associate Professor of Geological Sciences
Howard Dewald
Interim Dean, College of Arts and Sciences 3 Abstract
KLINGENSMITH, BRANDON C., M.S., August 2011, Geological Sciences
GIS Based Biogeography of Cincinnatian (Upper Ordovician) Brachiopods with Special
Reference to Hebertella
Director of Thesis: Alycia L. Stigall
Geographic ranges of type-Cincinnatian brachiopod species were reconstructed using Geographic Information Systems in order to analyze geographic distributions through space and time. Area polygons were digitized around species occurrence points plotted on the Cincinnatian outcrop belt (Ohio, Kentucky, Indiana), resulting in almost
100 individual maps spanning four depositional sequences. Individual species displayed patterns of habitat tracking as well as range expansion and contraction in response to regional sea level fluctuations. Statistical results show that species that established large geographic ranges preferentially survived the influx of extra-basinal species during the
Richmondian Invasion.
A systematic revision of the North American articulated brachiopod genus
Hebertella Hall and Clarke is proposed. Specimens representing 13 species were coded for morphologic character analysis. A single most parsimonious tree produced from analysis of character data shows the evolution of characters. Biogeographic patterns derived from the cladogram as well as those analyzed in the previous study suggest east to mid-continent dispersal of Hebertella species from the Middle to Late Ordovician.
Approved: ______
Alycia L. Stigall
Associate Professor of Geological Sciences 4 Acknowledgments
Research was funded in part by grants from the Ohio University Alumni
Association and the Geological Society of America. Research assistance and access to types was provided generously by archivists and collection managers at numerous institutions including the Cincinnati Museum Center, the Orton Geological Museum at the Ohio State University, the Limper Museum at Miami University, the Carnegie
Museum of Natural History, the American Museum of Natural History, The Academy of
Natural Sciences, the Museum of Comparative Zoology at Harvard University, and the
National Museum of Natural History.
For good company in the lab and field I am grateful to Katilin Maguire and
Kristen Everman. In my academic training I was inspired by the entire faculty in the
Department of Geological Sciences at Ohio University and hope them the very best.
For friendship and moral support during the writing of this thesis I thank John F. Taylor,
Jeremy Bader, and our cronies back in PA. Thanks are also given to Tom Dutro and John
Pojeta for help at the NMNH; Jim Loch, John Repetski, Dave Brezinski, Jim Miller, Joe
Clark, Charlie Burger, and Bob Kervin for their good wishes.
Naturally, I am deeply indebted to my advisor Alycia L. Stigall. She presents quality science, while demonstrating patience and an unparalleled love and mastery of the science in which she is a pioneer. I owe the gratitude of an advisee whose life has been forged by opportunities made possible by her generosity. I wish you and your family joy and happiness.
To my family and close friends, I owe just about everything else.
5 Table of Contents Page
Abstract ...... 3 Acknowledgments...... 4 List of Tables ...... 7 List of Figures ...... 8 Chapter 1: Introduction ...... 9 Chapter 2: GIS Based Analysis of Brachiopod Paleobiogeographic Patterns Across the Maysvillian to Richmondian Transition ...... 11 Abstract ...... 11 Introduction ...... 12 Background ...... 15 Geologic Setting ...... 15 The Biota ...... 20 The Richmondian Invasion and Extinction Interval ...... 20 Methods ...... 21 Geographic Extent ...... 21 Temporal Range ...... 23 Species Occurrence Information ...... 24 Range Reconstruction ...... 25 Stratigraphic Biases ...... 27 Statistical Analysis ...... 27 Results ...... 29 Sea-Level Versus Geographic Range ...... 29 Geographic Range Versus Survivorship ...... 30 Habitat Tracking ...... 32 Discussion ...... 35 Habitat Tracking vs. Speciation ...... 36 Geographic Range and Sea Level ...... 38 Geographic Range and Survival ...... 39 Conclusions ...... 40 6 Chapter 3: Phylogenetic Revision of the Middle and Late Ordovician Brachiopod Hebertella From North America ...... 43 Abstract ...... 43 Introduction ...... 43 Phylogenetic Analysis ...... 44 Description of Genus ...... 44 Investigated Taxa ...... 45 Characters and Character States ...... 47 Characters Analyzed ...... 49 Parsimony Analysis ...... 55 Results ...... 57 Evolutionary and Biogeographic Implications ...... 59 Systematic Paleontology ...... 63 Chapter 4: Conclusions ...... 70 References ...... 74 Appendix 1: Cincinnatian Brachiopod Database ...... 84 Appendix 2: Geographic Area of Species Range Polygons...... 141
7 List of Tables
Tables Page
1. Species based stratigraphic range chart……………………………………………...22
2. ANOVA table for analysis of species range versus standardized sea level…….……30
3. Comparison of mean range of survivors versus invading species…………...…...... 31
4. Data range of morphometric characters of species analyzed………………...…...….52
5. Statistical separaton of morphometric characters………………………...…....….....53
6. Character state distribution for taxa analyzed………………………………...…..…54
8 List of Figures
Figures Page
1. Cincinnatian time scale and sequence stratigraphy ...... 15
2. Cincinnatian outcrop belt and species occurrences ...... 16
3. Stages in geographic range reconstruction ...... 18
4. Range reconstruction of Hebertella occidentalis and others………...……..………..33
5. Range reconstruction of Platystrophia ponderosa and others……………….………34
6. Location of morphological measurements…………………….………………..……48
7. Single most parsimonious cladogram of Hebertella ………...……………..…….….56
8. Phylogenetic relationship of Hebertella with general biogeography…………..……60
9. Plate of representative Hebertella types…………………………………….….……62
9 Chapter 1: Introduction
Paleontologists have developed great interest in detailed studies of species level biogeography and evolution using modern paleontologic methods. Such studies require new approaches to paleontology that combine conventional methods with more contemporary, computer based analytical approaches. Methods utilizing Geographic
Information Systems (GIS) provides a medium to analyze large amounts of data while also providing the user with complete control over mapping that requires the geologic intuition and interpretations of a human user.
Such studies require testing grounds in which to analyze the consistency and general robustness of these methods; field areas with abundant fossils and thick stratigraphic sections representing millions of years of fairly continuous sedimentation.
The type-Cincinnatian of Ohio, Indiana and Kentucky is a well-studied, relatively complete succession of Late Ordovician strata. The type-Cincinnatian consists of thin, interbedded packstones and mudstones that appear to have“layer cake” architecture
(Davis and Cuffey 1998); however, deposition on a storm dominated, gently dipping carbonate-siliciclastic ramp creates environmental dynamicism which can be quantified and related to the dynamics of the native species.
The type-Cincinnatian not only provides an ideal location for this study, it also provides a time transgressive assemblages of biota. The brachiopod, which is easily identifiable in the field, diverse, and abundant, is the most useful taxon for this study.
Over a century and a half’s worth of fossil collections from the museums with the largest of these collections were visited for fossil occurrence data, which will serve in multiple projects beyond the scope of this thesis volume. 10 In this thesis, I have illustrated that GIS methods are amenable to paleontology by examining biogeographic patterns of fossil brachiopods within a spatial and temporal framework. I will discuss the relationship between species geographic ranges and the environment; particularly the correlation between the size and lateral placement of a species range and water depth. Additionally, discussion on how the size of a native species’ range affects whether it has the ability to resist extinction across the
Richmondian Invasion interval.
A phylogenetic analysis of species within the genus Hebertella is also introduced in this volume. I utilize character state analysis to produce a species level phylogeny in order to discover the relatedness of the species’ within this genus. Previous analyses of this genus (Walker 1982) using more conventional methods have revised few species, however, this is the most comprehensive study of this genus. Using character state analysis, I confirmed the Walker’s (1982) synonymy of H. occidentalis , thus removing the species name H. sinuata from the genus and from H. prestonensis . Additionally,
Mimella (Hebertella ) melonica was removed from the ingroup genus Hebertella and placed into the outgroup genus Mimella . By using the most parsimonious cladogram as well as biogeographic information from chapter two, I then discuss the overall genus in a biogeographic context. Having already noticed biogeographic patterns of a few
Hebertella species within the second chapter of the thesis, such as invasion, habitat tracking, and extinction, I attempt to construct a biogeographic account of the genus that incorporates its evolutionary history. Overall, within this thesis volume, I combine conventional paleontologic techniques with more recently developed methods in paleobiogeography and cladistics. 11 Chapter 2: GIS Based Analysis of Brachiopod Paleobiogeographic Patterns Across
the Maysvillian to Richmondian Transition
Abstract
The Late Ordovician was a time of active tectonism in the eastern United States, which greatly contributed to the development of intercontinental basins and arches that hosted invertebrate communities susceptible to frequent changes in the environment. This study focuses on the Late Ordovician (Maysvillian-Richmondian) brachiopod fauna of the Cincinnati region (Ohio, Indiana, Kentucky area) which inhabited a shallow marine carbonate-siliciclastic ramp. This analysis investigates the relationship between changes in relative sea-level, the geographic extent of species ranges, and relationship between these parameters and the relative survival of brachiopod species native to the Cincinnati
Arch region during the Richmondian invasion.
Species ranges were reconstructed both spatially and temporally (following the sequence stratigraphic framework of Holland [1993]) using a Geographic Information
System to quantitatively derive the geographic area of species ranges and describe lateral migration patterns in response to regional sea-level fluctuation. Geographic extent of species' ranges across multiple time slices enabled analysis of habitat tracking patterns, which were examined through “time-slice” animations, as well as their close link to sea- level through statistical analyses.
Results of statistical analyses support the link between species' geographic ranges and regional sea-level fluctuation; geographic range expanded as water depth increased with relative sea-level rise. Species also tracked preferred habitats by lateral migration 12 along the carbonate-siliciclastic ramp in response to sea-level change. Individual species, as well as much of the total population within each chronostratigraphic time-slice, displayed congruent patterns of movement throughout the Cincinnati Arch. The
Richmondian Invasion, an influx of species into the Cincinnati Arch, resulted in regional extinction and the eventual replacement of many native species with immigrant taxa.
Results of statistical analyses indicate that the native species which persisted into the
Richmondian were only those with large geographic ranges. This suggests species with larger ranges, typically generalists, were best able to compete in the new invasive regime.
Introduction
The strata of the Cincinnati Arch comprise some of the best known highly fossiliferous strata in North America. The units have been extensively studied in terms of biodiversity, paleoecology, and sequence stratigraphy (e.g., Holland 1993; Brett 1998;
Novack-Gottshall and Miller 2003). Sea-level fluctuations during the Cincinnatian Series
(Late Ordovician) instigated a series of faunal turnover events in the Cincinnati, Ohio region including interbasinal species invasion, species range size fluctuations, and species migrations due to habitat tracking.
The boundary between the two stages of the Cincinnati Series, the Maysvillian and the Richmondian, is marked by an influx of extra-basinal species known as the
Richmondian Invasion (Patzkowsky and Holland 1996, 1997). The effects of the species invasion on paleoecology and biodiversity have been well characterized (e.g.,
Patzkowsky and Holland, 1996, 1997; Holland and Patzkowsky, 2006). Previous studies have examined biogeographic patterns in terms of species preferred depth gradients along 13 the Cincinnatian ramp system (Holland 1995). No prior analyses, however, have considered biogeographic patterns in terms of areal extent of species ranges at the level of individual species at fine spatial and temporal scales. Utilizing Geographic Information
Systems (GIS) based mapping of the Cincinnatian fossil fauna, this study investigates paleobiogeographic patterns during an episode of interbasinal species invasion during the
Cincinnatian.
Several hypotheses were tested to examine the factors that may have contributed to changes in the geographic ranges of species. In particular, the relationship between species’ ranges and regional sea-level fluctuation, habitat tracking, and relative survival of extra-basinal invaders versus endemic species across the Maysvillian/Richmondian boundary are investigated. Incorporating Geographic Information System (GIS) methods into a paleobiogeographic framework provides a means to visually and quantitatively analyze the relationship between geographic range and changes in the environment.
Reconstructing geographic ranges of taxa is a key feature of biogeography and is evolving through advancements made in GIS methods. GIS methods in paleontology have recently been implemented in order to quantitatively examine biogeographic (e.g.
Rode and Lieberman 2004, 2005; Stigall Rode 2005; Stigall Rode and Lieberman 2005;
Stigall and Lieberman 2006) and stratigraphic (Rayfield 2005) hypotheses at the level of genus or species temporal intervals equivalent to biostratigraphic zones. Previous studies have successfully utilized GIS to investigate the relationship between Late Devonian brachiopod and bivalve paleobiogeography and environmental changes (Rode and
Lieberman 2004; Stigall Rode and Lieberman 2005; Stigall and Lieberman 2006). This study utilizes the methods developed in Rode and Lieberman (2004) to investigate Late 14 Ordovician brachiopod biogeography (in the Cincinnati Arch) across the Richmondian
Invasion interval. The focus of this study is to reconstruct, quantify, and statistically analyze the geographic ranges of articulate brachiopod species for four time intervals
(sequences C1-C4 of Holland [1993], Fig. 1) spanning the Maysvillian to Richmondian transition. By combining GIS with established paleobiogeographic techniques across a major crisis interval, the Richmondian Invasion, insight into the factors (biotic, abiotic, and contingent) that hinder species distribution and survival can be attained. By quantifying the relationship between environmental factors and the distribution of organisms (e.g. Lieberman and Stigall Rode 2005), the results of this study can provide insight into the mechanisms that contribute to other past crises as well as the modern biodiversity crisis.
15
Figure 1: Cincinnatian time scale, sequence based stratigraphic units, and traditional lithostratigraphic framework (Adapted from Holland [1993]). The column on the right represents a simplified water depth curve with standardized sea level values used in the statistical analyses discussed below.
Background
Geologic setting
The Cincinnati Series is exposed along the axis of a doubly plunging arch, the
Cincinnati Arch, which crosses the states of Ohio, Indiana, and Kentucky (Figure 2). The elongated structural arch is the remnant of interbasinal peripheral upwarping during the docking of the Taconic landmass to the Laurentian continent (Beaumont 1981; Quinlan and Beaumont 1984; Tankard 1986). Subsequent weathering and erosion of the arch exposed the underlying Ordovician section. Stratigraphic work by Holland (1993) and
U-Pb zircon dating (Tucker and McKerrow 1995) places the Cincinnatian within a second-order supersequence (Taconic) at approximately 454 to 443.3 Ma (Holland et al.
1997; Wilson et al. 1999). 16
OHIO
INDIANA
50km FormationsTime slices
LibertyC4 (b) WaynesvilleC4 (a) ArnheimC3 KENTUCKY McMillanC2 FairviewC1
Figure 2: Geographic extent of the Cincinnatian outcrop belt (yellow). Circles represent collection localities for species included in this analysis coded by temporal interval. Cincinnatian strata are absent from the center of the arch, where Middle Ordovician strata are exposed, and are poorly exposed on the south side of the arch in central Kentucky. This study, therefore, focuses on the northern half of the Cincinnati arch. 17 The tectonic positions of the major Ordovician continents are shown in Figure 3.
Eastern North America was part of the supercontinent Laurentia. It was located about 20 degrees south of the equator and rotated slightly clockwise of its present orientation
(Scotese and McKerrow 1991; Figure 3). Laurentia was mostly covered by an extensive shallow epicontinental sea that was punctuated by a system of sub-basins and tectonic arches which sustained a complex and rich diversity of taxa (Feldman 1996; Davis 1998).
The Laurentian continent was surrounded by micro-continents (Siberia, Baltica,
Avalonia), and an island arc (Piedmont Arc) on the present day east coast. The accretion of the island arc to Laurentia in the Middle to Late Ordovician resulted in uplift of the
Taconic Mountains (Beaumont 1981; Quinlan and Beaumont 1984; Tankard 1986) on the present day east coast. Contemporaneous shedding of detrital sediment from the highlands onto the platform created a mixed carbonate-siliciclastic ramp system in what is now the eastern United States.
During the Ordovician, the current day Cincinnati Arch was a northward dipping carbonate-siliciclastic ramp (Tobin and Pryor 1985; Jennette and Pryor 1993; Holland
1993; Miller et al. 2001), situated on the peripheral forebulge of the Taconic orogenic system (DeCelles and Giles 1996). Lithofacies and biofacies were elongate belts oriented parallel to the shoreline, and laterally migrated up (shoreward) and down (seaward) the ramp in response to localized fluctuation of sea-level (Holland 1993). Rock types in the study area are cyclic (Tobin and Pryor 1985), and predominantly claystones and fossiliferous packstones deposited typically between normal and storm wavebases
(Wilson et al. 1999). 18
B A
C
Figure 3: Stages in geographic range reconstruction. A) All data mapped onto the modern continental configuration. B) Data rotated onto a paleogeographic reconstruction for the Late Ordovician continental configuration. C) Polygon representing the geographic range of Zygospira modesta (C2 time slice). Species occurrence points are shown in red and the minimum area polygon in blue. 19 Storm events have been singled out as the predominant influence on Cincinnatian depositional patterns (Diekmeyer 1998). The propagation of hurricanes intersecting the northwest sloping ramp perpendicular to shoreline produced tempestites, or storm deposits, which yield high agglomerations of local biogenic debris in distal locations on the ramp (Diekmeyer 1998). Although many of the tempestite beds show the effects of storm reworking over several meters, most represent essentially in-situ association of species on the ramp (Frey 1987). Background sedimentation from the Taconic highlands resulted in siliciclastic mud accumulations, which blanketed the shell lags and tempestites as storms waned.
Faunal transitions throughout successive strata correspond to an increase or decrease in energy related to shallowing or deepening conditions. Shallowing environments were prone to regular reworking events, typically hurricanes, which modified the substrate from a muddy bottom to shelly pavements (Diekmeyer 1998).
These shelly accumulations become increasingly amalgamated upsection. In effect, faunal assemblages range from organisms associated with relatively deep, low energy, soft substrate conditions to those associated with higher energy, firmer substrate environments (Diekmeyer 1998). The shale to limestone ratio of the alternating limestone-shale bedding can be considered to represent a proxy for water depth (more shale = deeper, more limestone = shallower), and this ratio has been incorporated into sequence stratigraphic interprerations as well as for formation identification (Holland
1993).
20 The biota
The shallow Cincinnatian ramp system sustained a diverse association of invertebrates, typical of the Ordovician. Invertebrate communities are dominated by brachiopods, bryozoans, stalked and encrusting echinoderms, trilobites, and mollusks (Frey 1987;
Cuffey 1998; Wilson et al. 1999). This study emphasizes articulate brachiopod species.
Brachiopods were the most abundant benthic components of Late Ordovician marine shelf environments (Sheehan 2001; Harper et al. 2004), ranging from the deep, low energy, soft substrate environments to the shallower, high energy, shelly pavements discussed above. Due to their (epibenthic or shallow endobenthic) life habitat, brachiopod fossils are likely to closely reflect their actual living distribution (Kidwell and
Flessa 1995). In addition, their abundance, ease of identification, and sensitivity to environmental changes (see discussion) make brachiopods the best candidate for reconstructing species geographic ranges for this study. The aim of this project is to produce the most accurate reconstructions of species-level ranges possible using GIS.
Therefore, the geographic ranges of articulate brachiopod species were modeled.
The Richmondian Invasion and extinction interval
Upper Ordovician biofacies are composed of communities that were not tightly integrated in structure, but were fluid with genera and species that moved in and out of communities in response to local changes in environmental conditions (Patzkowsky and
Holland 1999; Brett et al. 2007). The base of the Richmondian includes a well- characterized species invasion event (Holland 1997, 2005; Patzkowky 2004) displaying extensive biofacies replacement, turnover (Patzkowsky 2004), and diversification at the 21 species through class level (Holland 1997). Holland (1997) describes the Richmondian
Invasion as in influx of western brachiopod taxa associated with the transgression at the beginning of the C3 sequence and suggests barriers to dispersal were broken down with rising sea levels. Holland further suggests that the thermal barriers separating the western
(northern Canada, Wyoming, Colorado, South Dakota, Texas, Iowa, and Minnesota) or
“Arctic” fauna were reduced by the transgression (Holland 1997).
The invasive taxa, which include tabulate corals, nautiloids, trilobites, and brachiopods, first appear in the C3 sequence but become more abundant across the C4 sequence (Holland 1997). The timing of the invasion was a single episode of faunal introductions, regardless of its gradual nature in single outcrops (Holland 1997). The onset of invasion was at the C3 sequence (Maysvillian/Richmondian boundary), but the majority of the new brachiopod species come into view at the C4 sequence (see Table 1), suggesting a single event followed by gradual range expansion.
Methods
Geographic extent
The geographic extent of this study is the type-Cincinnatian, which is exposed at the apex of the Cincinnati Arch, crossing into the states of Ohio, Indiana, and Kentucky
(Figure 2). Brachiopods from the type-Cincinnatian are abundant, well preserved, and may be identified with relative ease. Museum collections were essential to the completion of this study. Over a century and a half of labeled specimens are archived in these collections; however, the majority of collections are from the immediate vicinity of
Cincinnati. 22 Table 1: Stratigraphic range chart of brachiopod species included in this study. Species are identified as native to the Cincinnati area ( ), descendant of Cincinnati natives (†), or extrabasinal invaders (*).
a b 23 The northern half of the arch is much better sampled due to more complete exposures.
Targeted field work in central Kentucky was unable to produce sufficient data to create a compatible data set with the northern exposure. This study, therefore, focuses on the section of the outcrop belt in Ohio, northern Kentucky, and Indiana where there is ample spatial and temporal coverage (Fig. 2).
Temporal range
Four time intervals based on depositional sequences, delineated by Holland
(1993; Figure 1), were used to examine the change in the geographic distribution of a species range through time. The intervals examined are, from oldest to youngest, the C1 through C4 sequences, which vary from 1 to 6 Ma in duration (Holland 1993, 1998). In the type-Cincinnatian area, the longest sequence (C1) is approximately 6 Ma in duration, and is composed of the Kope, Fairview, and Bellevue Formations. The C2 and C3 sequences, each approximately 1.5 Ma in duration, contain the Corryville/Mt. Auburn and “Sunset”/Oregonia Formations. The C4 sequence, is approximately 2 Ma in duration, and spans the majority of the Richmondian Stage, including the Waynesville,
Liberty, and Lower Whitewater Formations. Sequence boundaries are used to subdivide time slices in this analysis, because they represent the most laterally extensive, chronostratigraphic horizons available within the type-Cincinnatian section. All four studied sequence boundaries coincide with transgressive surfaces, distinguished as sharp disconformable surfaces that cap shallowing-upward successions (Holland 1993).
24 Species occurrence information
The primary data required for GIS analysis are the temporal and spatial occurrences of species. The occurrence data include: (1) species level identification, (2) stratigraphic position, and (3) geographic location from which the specimen was collected. The primary data set was derived from museum collections. Museums with extensive Cincinnatian collections were targeted for inclusion in this project and include:
The Cincinnati Museum Center; the Orton Geological Museum (the Ohio State
University); and the Carl Limper Geology Museum (Miami University). The database and all included collection information are in Appendix 1. Species identifications were verified using the most recent taxonomic guides for Cincinnatian fossil identification
(Shrake 1992; Feldmann et al. 1996; Davis 1998).
Geographic location data were converted to latitude and longitude values with quadrangles and up-to-date georeferencing programs and queries, including NASA
World Wind 1.3.3.1 (NASA 2005), Google Earth 3.0 (Google 2005), MapSource
MetroGuide North America v8 (Garmin 2006), and US Board on Geographic Names
(USGS/BGN). Collections were only added to the database if they had sufficient stratigraphic and geographic information to be placed within a defined geographic region and within the preset time-slices.
In addition to the museum collections, field data were also collected throughout the Cincinnati Arch in order to adequately cover gaps within the stratigraphic and geographic dataset. Field locations focused on and around sites described in field guidebooks (Shrake 1992; Davis and Cuffey 1998) in order to maintain stratigraphic accuracy. Field geographic data were collected using a Garmin GPS unit, which 25 provided the latitude and longitude coordinates needed. Targeted field locations included sites in Ohio (Caesar Creek, Cowan Lake), Kentucky (Maysville, Riedlin/Mason Road,
Bedford), and Indiana (Madison, South Gate Hill, Brookville, Bon Well Hill, Garr
Hill/Brookville North, Richmond). Species occurrence data are presented in Appendix 1.
Range Reconstruction
Once the species occurrence data were assembled into a database, the information was imported into a Geographic Information Systems (GIS). A GIS is a digital database which enables the user to upload and project geographic datasets onto visual layers that may be queried for statistical information, such as the area of a geographic species range represented by an enclosed polygon. Within the GIS program, the spatial and temporal information associated with our fossil collection data was transferred from the database onto digital layers that were projected onto digital maps. Reconstructing the geographic range of all species by the bounding-polygon method required four steps: (1) georeference the location data into latitudes and longitudes and map onto a modern continental configuration, (2) rotate the point data into a paleocontinental configuration,
(3) create polygons from the point data to represent the species range, and (4) calculate the area of the range polygon to be used for statistical comparisons. More detailed discussions of range reconstruction methods are presented in Rode and Lieberman (2004) and Stigall Rode (2005).
Once the data was georeferenced into latitudes and longitude coordinates, they were plotted onto a base map representing the modern Cincinnatian outcrop belt, using
ArcView GIS 3.2 (ESRI, 1999; Figure 1). The “total-coverage” map was imported into 26 PaleoGIS/ ArcView 3.5 (Ross and Scotese, 2000) and the data rotated into a paleocontinental configuration, equivalent to the Ashgillian System (approximately 448
Ma; Figure 3). An example of a reconstructed time slice is shown in Figure 3. The global reconstruction derived from Ross and Scotese (2000) is based on the underlying data from the PaleoMap project of Scotese (1998) and is reconstructed using several data sources outlined in Scotese (2004), including: (1) linear magnetic anomalies produced by sea floor spreading, (2) paleomagnetism, (3) hotspot tracks and large igneous provinces,
(4) the tectonic fabric of the ocean floor mapped by satellite altimetry, (5) lithologic indicators of climate, and (6) the geologic record of plate tectonic history. For this analysis, maps were constructed for eight formations (Fairview through Lower
Whitewater) and consolidated into four time slices based on the depositional sequences described above (Holland 1993). After all point data were reconstructed to Ashgillian time, the rotated data points were exported into ArcView GIS 9.1 (ESRI, 2005) for analysis.
Point data were organized into layers (time slices) and sublayers (species) within
ArcMap (ESRI, 2005). The organization of these layers provided the capacity to switch on or off a particular species occurrence for a time slice. Using the polygon tools provided in the GIS software, range polygons were constructed by enclosing the species occurrences within a polygon for every species and formation. The polygons were drawn to encompass all points (Figure 2c), using as many points as nodes as possible, in order to reconstruct the smallest polygon possible for the set of occurrence localities. This method was used in an attempt to eliminate variation due to the over- or under-estimation of the range. Once the polygons were complete for each species in every formation, the 27 area of each range was calculated as a numerical area value (in kilometers squared).
Reconstructed species range maps are presented in ArcView and calculated areas for all species ranges are presented in Appendix 2. By assigning each polygon an area value, changes in range size can be described quantitatively and compared to environmental parameters.
Stratigraphic biases
The temporal resolution chosen for this study was the depositional sequences of
Holland (1993). Sequence stratigraphy divides the stratigraphic record into genetically related strata bounded by physical unconformities (Mitchum 1977). Because each unconformity separates older from younger strata, the unconformities and their correlative conformities are chronostratigraphically significant (North American
Commission on Stratigraphic Nomenclature 1983). The Cincinnatian formations are laterally discontinuous throughout the study area, so by using depositional sequences as time slices, lateral discontinuity is significantly reduced. The museum collections were originally labeled by formation and are, thus, recorded in the collection database by formation. For the study, formations were grouped as sequence packages to improve lateral continuity and project a truer representation of total collection coverage.
Statistical analysis
The GIS can be used to quantify reconstructed species ranges so that values are amenable to statistical analysis and hypothesis testing (Stigall and Lieberman 2006). The
GIS is used to calculate the range (area) values for each polygon, representing an 28 individual species range for each time slice. These data, which includes both spatial and temporal data, are tested against environmental variables, to determine whether environmental factors are related to changes in species range. In this case, regional water depth is analyzed as the environmental factor, since it is thought to influence the size of species ranges in the type-Cincinnatian (Holland 2002). Although water depth itself is not the controlling factor of the distribution taxa, other factors such as temperature, salinity, light, shear stress, nutrients, and substrate vary in response to water depth.
Therefore, water depth may serve as a proxy summarizing the changes in these environmental variables (Holland 1995).
The regional water depth curve developed by Holland (1993; Figure1) was utilized in this analysis because its temporal resolution matches that of our study.
Additionally, this regional water depth curve has excellent lithologic and biostratigraphic control and was constructed based on the C1-C4 sequences, which are used in this analysis. The sequence boundaries provide the necessary chronostratigraphic intervals for “time-slice” analysis. For each time slice, the maximum reach (maximum flooding surface) of the curve was assigned a relative numerical value normalized by the overall highest peak on the curve (C1), which is assigned 100. The values 39, 24, and 62 were assigned to the C2, C3, and C4 time slices (sequences) in succession (Fig.1).
All statistical analyses were performed using Minitab 15.1 (Minitab 2006).
Analysis of variance (ANOVA) was used to analyze the relationship between species range and sea-level. To test the relationship between geographic range and survivorship of native species, Student t-tests were conducted to determine whether a statistical difference existed in the mean range of invasive and native species for each time slice 29 following the Richmondian Invasion. In addition, the Bonferroni correction was applied to compare the multiple t-tests used for each interval.
Results
Sea-level versus geographic range
The area values calculated for the geographic range polygons of each species were statistically compared to the standardized values for water depth during each time slice in which each species is represented (Table 2). Analysis of variance was performed to relate mean species ranges for each time slice with the standardized sea level value associated with the time slice (depositional sequence). The relationship between mean geographic range and standardized sea-level is marginally significant (p=0.079) (Table
2). Changes in relative sea-level will result in concomitant increase or decrease in the geographic ranges of species due to changes in the size of the habitable area.
30 Table 2: ANOVA table for analysis of species range versus standardized sea level
Degrees of Sum of Mean freedom squares squares F-value p-Value
Regression 1 1398.3 1398.29 3.15 0.079 Residual 78 34615.5 443.78 Total 79 36013.8
Geographic range versus survivorship
The Richmondian Invasion was followed by faunal turnover resulting in extinction of the majority of the Maysvillian fauna; replacing them with extrabasinal species. There were, however, some native taxa that persisted, relatively unaffected, into the Richmondian from the Maysvillian, such as Platystrophia (=Vinlandostrophia of
Vostoy and Harper [2007]) and Hebertella . The response of a species across this boundary is characterized by whether a species persisted into the Richmondian as a survivor, or a victim if they went extinct at the beginning of the Richmondian. We hypothesized that species that exhibit a large geographic range will preferentially survive the Richmondian Invasion. Comparing the mean geographic range of species per interval, it was found that native species that persisted into the Richmondian exhibit larger geographic ranges than those of invading species (p=0.044; Table 3). Presumably, generalist ecologies of these species provided a preadaptation that allowed these species to successfully compete with the new invasive species. 31 Table 3: Comparison of the mean geographic range (in km 2) of native survivors versus invading species. Student t-tests for each time slice post-invasion initiation are shown.
32 Habitat tracking
The same mechanisms that drive the water depth cycles in the Cincinnatian Series might also control long-term ecological processes such as migration, or habitat tracking.
As sea-level rises and falls on a ramp system, the parallel lithofacies migrate shoreward and basinward. Species may react to this environmental change by either (1) migrating to track a preferred habitat (laterally along the ramp) in an unchanged relationship with their environment of adaptation (Gould 2007), (2) evolve adaptations to new environmental conditions, or (3) by becoming extinct (Brett et al. 2007).
Species migration, known as habitat tracking, can be discerned through the use of time-sliced animations in the GIS. As a species preferred habitat becomes unavailable or moves laterally to another location, habitat tracking would be indicated if species’ geographic range shifts laterally, conversely, species may maintain the position of their original geographic range while increasing or decreasing the size of its range. Figure 4 demonstrates lateral migration of Hebertella occidentalis through time, while on the other hand, species such as Platystrophia ponderosa (Figure 5) remain stationary while increasing or decreasing its range through time. An equal amount of species share patterns that are more similar to either H. occidentalis or P. ponderosa. Species that display similar patterns to H. occidentalis include: Onniella meeki, Rhynchotrema dentatum, Platystrophia cypha, Strophomena planumbona, Rafinesquina ponderosa, and
Platystrophia clarksvillensis. Species that display patterns similar to P. ponderosa include: Rafinesquina alternata, Platystrophia laticosta, Zygospira modesta, and
Glyptorthis insculpta.
33
50 50 50 50 50 C1 km C2 km C3 km C4a km C4b km
50 50 50 50 C2 km C3 km C4a km C4b km
50 50 50 50 C2 km C3 km C4a km C4b km
50 C4a 50 C3 km km
Figure 4: Range reconstruction of Hebertella occidentalis (row 1), Onniella meeki (row 2), Platystrophia cypha (row 3), Rhynchotrema dentatum (row 4) from the C1 through C4b time slice (sequence). These taxa display range expansion and contraction in response to sea level fluctuation as well as a clearly defined tracking patterns. As carryover species, range expansion pre-dates the invasion, followed by contraction during the invasion, and subsequent tracking northwest with a rise in water depth. R. dentatum , as an invader, displays similar patterns compared to the native species.
34
50 50 50 50 C1 km C2 km C3 km C4a km
50 50 50 C2 km C3 km C4a km
50 50 50 C3 km C4a km C4b km
Figure 5: Range reconstruction of Platystrophia ponderosa (row 1), Zygospira modesta (row 2), Glyptorthis insculpta (row 3), from the C1 through C4b time slice (sequence). The geographic ranges of these taxa expand and contract in response to sea level very well. The center of the range is geographically stable, but the margins expand and contract through time.
35 Discussion
Based on the results of the statistical analyses presented above, relative sea-level and the geographic area inhabited by indigenous species had significant effects on the geographic range of a species and survivorship in the Cincinnatian. The ability of a species to occupy a large geographic area and inhabit a favorable environment made it a candidate for species survival during a biotic crisis, such as the Richmondian Invasion.
The trend of mean species geographic range from the C1 through the C4 sequence intervals follows the water depth curve of Holland (1993; Figure 3) with reasonable statistical significance. This congruence indicates that the geographic range of a species is affected by the regional fluctuation of sea level. With a rise in sea level, the range of a species increases, and decreases during a sea level fall. Range expansion can be explained due to the increasing amount of the species habitual range made available as there is an increased water depth on the ramp. Additionally, geographic range contraction was associated with the decrease of species habitat as there was a decreased water depth on the ramp.
In addition to range expansion and contraction, lateral translations of ranges indicate habitat tracking and propagation in response to the lateral migration of the preferred biotic habitat up and down the ramp. This phenomenon can be predicted within any highstand and lowstand systems tracts and can be seen throughout a majority of the time-sliced species reconstructions created in this project. For example, Hebertella occidentalis (Figure 2.4) displays both patterns of range expansion and contraction as well as lateral migration patterns. 36 Biogeographic change indicated by habitat tracking in a complex basin implies opportunity for peripheral isolate formation and speciation (Morris et al. 1995). In addition, a large increase in sea level may allow the barriers between basins to be penetrated, and thus increase the opportunity for invasive speciation and subsequent extinction within adjacent basins (e.g., Rode and Lieberman 2004).
Geographic range also played an important role in determining species survival through the Richmondian biodiversity crisis interval. During a species invasion interval, species with smaller geographic ranges are, on average, more prone to extinction than those with larger ranges (Jablonski 1986; 1989; Rode and Lieberman 2004). Although invasive species may create an added competitive environment to any modern or fossil ecosystem, certain particular species and genera may persist if they have established a large geographic range as an ecological generalist (Rode and Lieberman 2004).
Habitat tracking vs. speciation
Tracking implies that species generally respond to long-term physical changes in the environment. The response is not fundamentally accompanied by adaptation. Instead, species will primarily migrate or track a preferred habitat, if the rate and magnitude of environmental change does not exceed the ability of a species to respond (Brett et al.
2007). Lateral migration of parallel biofacies belts in response to sea level oscillations yield a predictable pattern of habitat tracking, which is typical of many marine benthic communities (Brett 1998).
Prior to the use of GIS techniques, analyses that have demonstrated lateral migrations of species through time have been limited to time-geography plots made from 37 the occurrence and recurrence of species through stratigraphic sections, or the reconstruction of ranges occupied by higher taxa (e.g. Webby 1992), such as families and orders over millions to tens of millions of years. By using GIS methods, species distributions are illustrated and analyzed in a four-dimensional representation. Although we do expect taphonomic or stratigraphic biases while interpreting geographic changes in species range, it should be noted that geographic species range migration patterns do not occur because of simple shifts of facies. Habitat tracking patterns represent an absence of occurrence within the successive strata and facies at the location in which the taxa was found previously.
From the C1 through the C4 time slice reconstructions (depositional sequences), the lateral displacement for species ranges was either narrow (tens of kilometers of migration perpendicular to shoreline) or on the order of hundreds of kilometers (basin- wide) over millions of years. The range reconstructions demonstrate two primary patterns: (1) a northward migration tract among individual species (e.g. Hebertella occidentalis ; Figure 4) and (2) temporal changes in which the center or bulk of the species’ range remains virtually fixed geographically but exhibits branching along the range margins (e.g. Platystrophia ponderosa ; Figure 5).
Inherent in the concept of habitat tracking is the concept of species migration without adaptation. Many Cincinnatian brachiopod species do behave in this way; however, species, such as Platystrophia ponderosa , that exhibit branching along their range margins have significant potential for population isolation in these regions that could potentially be followed by allopatric speciation. Several clades native to the
Cincinnati arch region experience speciation during the Richmondian, which may be 38 related to this type of range fragmentation. Species that are involved in either aspect of invasion, extinction, or subsequent speciation are noted in Table 1. In particular, the
Platystrophia species complex undergoes speciation, which may be related to the range fragmentation observed with GIS analysis.
Geographic range and sea level
The area that a species will inhabit is related to the area a species could inhabit and maintain a population (Brown and Lomolino, 1998). An increase in water depth on the Cincinnatian ramp system will cause the habitat of species that prefer relatively deep, low energy conditions to migrate to within the study site. Additionally, a decrease in water depth on the ramp will cause the habitat of species that prefer relatively shallow, high energy conditions to migrate to within the study site. Outside the study site, adjacent facies belts simultaneously display environmental conditions analogous to those present while the same facies appear within the study section. It was hypothesized that a sea level rise will cause an expansion of the habitable range of a species, thus increasing the geographic range of the species. On the other hand, a sea level fall will result in the contraction of the habitual range of the species, thus decreasing the geographic range of the species. Results of the statistical analyses presented above, confirm that geographic extents of species’ ranges were directly influenced by fluctuations in regional sea level.
There are, however, caveats associated with the confirmation of this hypothesis.
Changes in the size of the geographic ranges of each species are by no means regular.
The positive outcome of this experiment demonstrated that the general trend of the 39 population, as well as the individual species within display congruent trends as well as the utility of reconstructing range using a quantitative area-based polygon system. The pattern retrieved from the species range reconstructions may be partly dependent on distribution biases (Holland 1995; Holland and Patzkowsky 2002), over- and under- estimation of range (Stigall and Lieberman 2005), and the lateral cutoff of the outcrop belt in the center and edges of the Cincinnati Arch (Fig. 1). These potential problems have been addressed, and distribution biases have been reduced due to the high sampling resolution obtained in the study area from over a century of Cincinnatian research. The estimation of geographic range using the polygon enclosing method has been shown to be a strong predictor of actual species range when compared to a niche modeling program
(GARP; Stigall Rode and Lieberman 2005). Additionally, range polygons were digitally hand-drawn, in order to produce reconstructions that were best supported by the underlying biological and geological data, rather than simply relying on computer algorithms.
Geographic range and survival
Invasive species phenomena directly affect species survival and biodiversity mechanics through the Cincinnatian. Geographic range played an important role in determining species survival through the biodiversity crisis interval. A larger niche means larger geographic ranges of populations, and larger ranges mean an expectation of longer life for a species (Wilson 1999). When the species are categorized into two geographic range classes, the species with a broader geographic range are, on average, more likely to survive than species with narrower geographic ranges (which become 40 provincially extinct) across the Richmondian Invasion interval (see Table 2). This relationship suggests generalist species, whose ranges are facies independent; spanning several environmental zones, are more likely to survive in the invasive regime as opposed to specialist species with small ranges that persist within a single predictable environment. The correlation appears very general, yet, in previous studies, the link between geographic range extent and extinction is clear for a variety of assemblages
(Jackson 1974; Hansen 1978, 1980; Koch 1980; Jablonski 1986; Vrba 1987; Jablonski and Raup 1995; Rode and Lieberman 2004; Stigall Rode and Lieberman 2005).
This relation may have an element of bias, which incorporates sampling effects, facies control, and sequences. Species with a greater geographic range, and generalist ecologies, will have a greater probability of preservation in the fossil record, and may just appear to persist longer than species with a smaller geographic range (Gaston 1998).
This component of bias is unavoidable; however, the species associated with this study have been mapped for at least two sequences beyond the onset of the invasion interval
(three formations) in order to increase the chance of occurrence.
Conclusions
Lateral shifts in biofacies were found to represent the migration of species ranges in response to a congruent shift of a species preferred habitat. The majority of species displayed a northward migration of range through time or remained relatively stationary but developed branching margins to their geographic ranges. Standardized sea-level values from Holland (1993) were compared to the mean ranges of species during each time-slice in which a sea-level value was assigned. The geographic extent of species 41 ranges were found to be directly influenced by oscillations in sea-level, with reasonable statistical significance. The size of a species’ geographic range also played a key role in determining species survivorship across the Richmondian Invasion interval. With an influx of extra-basinal species, it was found that native species that had a relatively large range before the invasion proved to have an advantage over species with restricted geographic ranges. Native species with relatively small ranges before the invasion suffered extinction somewhere between the C3 and C5 sequence boundaries.
Paleontologic methods utilizing GIS have been relatively limited to date; however, recent studies have utilized GIS methods to quantitatively examine the association of geographic species ranges with respect to environmental parameters (Rode and Lieberman 2004; Stigall Rode and Lieberman 2005; Stigall Rode 2005). GIS analysis was utilized to examine how fossil brachiopod species ranges from the
Cincinnati Arch respond to an increased or decreased availability of habitat, laterally shifting habitats, and invasion of non-native species. The use of GIS provides a mechanism to illustrate geographic ranges from large data sets both spatially and temporally within a single dynamic program (Stigall and Lieberman 2006). In addition to being a dynamic database and cartographic tool, the quantitative data derived from the geographic range reconstructions can be tested statistically for use in hypothesis testing.
In this case, the area values associated with species polygons were used in conjunction with standardized sea level values in order to determine whether water depth had an influence on the geographic extent of the range. The same area values for the polygons were also separated into two categories, including native and invasive species. Results of 42 statistical analyses (Student t-test) indicate that species survival was influenced by the extent of the range.
Having successfully utilized GIS to estimate the spatial and temporal distribution of articulate brachiopod species in the type-Cincinnatian, as well as analyze the mechanism which influences change in the geographic range of species, future analysis using these methods may be applied. Niche modeling could be used to refine species ranges and tailor them more specifically to environmental parameters than by the enclosed polygon method (see Comparison of GARP and GIS enclosure ranges in Stigall
Rode and Lieberman 2005). Furthermore, analysis of additional taxa (e.g. bivalves, gastropods, trilobites) could be conducted or the the analysis expanded to include multiple basins (e.g. Appalachian Basin, Michigan Basin, Illinois Basin) and or larger geographic distances (e.g. worldwide). Results of multiple studies can be analyzed for general trends across several crisis intervals, so as to understand the underlying causes of biodiversity crises, and eventually, the modern biodiversity crisis.
43 Chapter 3: Phylogenetic revision of the Middle and Late Ordovician brachiopod
Hebertella from North America
Abstract
A systematic revision of the North American genus Hebertella Hall and Clarke
1892 is proposed. One Late Ordovician species, Hebertella pervetus Cooper, is moved to the genus Mimella . Hebertella occidentalis Hall and Hebertella sinuata Hall are synonymized, giving taxonomic preference to the name Hebertella occidentalis. Forms are discussed from western states (Iowa and Wisconsin) as well as the Cincinnati Arch
(Ohio, Indiana, Kentucky) and Central Basin (Tennessee) in an evolutionary and biogeographic context. Speciation events are related to geographic range expansion and invasion within the genus. Specific examples of species from the Cincinnati Arch have been studied across the Richmondian Invasion of the Cincinnatian Series to determine biogeographic patterns across a crisis interval.
Introduction
Hebertella Hall and Clarke (1892) is a common orthid brachiopod genus that persisted from the Middle through Late Ordovician in North America. Walker (1982) conducted a taxonomic study of three Hebertella species from the Lexington Limestone
(Middle Ordovician) and Late Ordovician rocks of Kentucky, however a comprehensive taxonomic revision of Middle and Upper Ordovician Hebertella had not been undertaken previously. This paper presents a phylogenetic analysis of Middle and Late Ordovician 44 Hebertella from North America to assess species validity and taxonomy within this genus.
In the past, the name Hebertella Hall and Clarke (1892) has been applied species within the genera Plectorthis, Mimella, Glyptorthis, Eridorthis, and Austinella due to general external similarities, although each of these genera are internally distinguishable
(Walker 1982). The last three genera were originally included by Hall and Clarke (1893) in their concept of Hebertella , but were later separated by Foerste (1909; 1914). Walker
(1982) described three new species of Hebertella and placed Hebertella sinuata (Hall),
Hebertella subjugata (Hall), and H. latisulcata (Foerste) in synonymy with Hebertella occidentalis (Hall).
Phylogenetic Analysis
Description of genus
Hebertella is a common Paleozoic orthid brachiopod recognized by its ventral- valve muscle field, which is medially divided by a prominent ridge upon the summit of which lies the scar of the adductors. It is also characterized by the profile of the ventral valve, which ranges from slightly convex to flat or slightly concave (Walker 1982). The ventral valve is always less convex than the dorsal valve which is frequently gibbous or inflated. All species of Hebertella are generally large in size, display a sinuous commissural trace due to the development of a sulcus and have numerous coarse costae.
Additional diagnostic features allow Hebertella species to be distinguished from one another. These include, among others, features of the internal muscle field and valve outline. The combination of occurrence of the various morphologic characters is most 45 important as there is no single key feature that is reliable (Walker 1982). In this analysis, type specimens of Hebertella species are distinguished not only by discrete characters, but also through quantitative analysis of morphologic features.
Investigated taxa
Specimens representing thirteen species of Hebertella were analyzed. Most species known from Middle and Upper Ordovician North America (those for which sufficient morphological information exists) were included in the phylogenetic analysis.
Hebertella occidentalis montoyensis Howe and Hebertella imperator Billings were not included in the analysis due to lack of sufficient morphologic data for character analysis.
Doleroides tennesseenisis , Doleroides winchelli , and Mimella extensa were chosen as the outgroup taxa for character polarization. Both Mimella and Dolerioides are assigned to the family Plectorthidae along with Hebertella. In addition, Mimella was chosen because the genus name Hebertella had once been applied to the genus Mimella (Walker 1982).
In fact, they were previously considered to be synonyms based on the size and shape of the shell, exterior ornamentation, and ventral muscle field. Furthermore, both outgroup taxa occur in Early to Middle Ordovician strata, which is older than the occurrence of
Hebertella . These taxa are likely to be either ancestral or sister taxa to Hebertella and are, therefore, appropriate outgroup taxa.
Type specimens of Hebertella species were examined from the following collections: American Museum of Natural History (AMNH); Carnegie Museum of
Natural History (CM); Harvard Museum of Comparative Zoology (MCZ); The Academy of Natural Sciences (ANSP); and the National Museum of Natural History (USNM). 46 This analysis focuses character assessment on specimens in the type series of each
Hebertella species, because they are the name bearers of the species, and contain all of the character traits of the species at the time of original description. The type series of most Hebertella species comprises multiple specimens, which provides additional information on intraspecific morphologic variation that occurs among several specimens of the same species from the same location. Supplementary specimens can supply additional information, though they do not bear equivalent taxonomic rank (International
Commission on Zoological Nomenclature 1999). Where present, additional specimens were examined to assess intraspecific variability, which is common in the genus (Walker
1982) .
Character analyses are made on the basis of multiple collections; however species represented by single, incomplete specimens or only external or internal molds are difficult to identify and lack more than half of the characters analyzed in this study.
Hebertella imperator and H. montoyensis were both excluded from analysis for this reason. Small Hebertella specimens are indistinguishable from Plectorthis (Walker
1982), and the two genera are considered to be closely related (Schuchert and Cooper
1932). To remove effects of ontogenetic variation on character coding, only specimens that represent full-grown individuals were considered. As the genus Hebertella is generally large, doubt concerning the maturity of Hebertella pervetus and Hebertella clermontensis type specimens arises due to their characteristically small shell size. They are, however, included in the analysis because several type specimens, including the original holotype are available for character coding. Furthermore, Hebertella sinuata ,
Hebertella occidentalis , and Hebertella subjugata were previously placed into synonymy 47 by Walker (1982), they were coded individually and analyzed separately in this analysis to assess the validity of Walker’s (1982) proposed synonomy and determine whether they group together within a phylogenetic framework.
Characters and character states
Previous studies have emphasized external characters in differentiating among
Hebertella species (e.g. Walker 1982). This study builds on that framework while also incorporating internal characters. Internal characters have been shown to be of particular phylogenetic significance in other genera of orthid brachipods (e.g., Vostoy and Harper,
2007). Parsimony analysis was conducted using 22 morphologic characters (listed below). Locations of measured features are illustrated in Figure 6. The data range of morphometric characters is displayed in Table 4, and the statistical separation between character states used in the analysis is presented in Table 5. The data matrix based on these characters is presented in Table 6. In some cases species exhibit multiple states for a single character; these taxa are treated as polymorphic with respect to given characters, and entered as such in the matrix (i.e. with an X or Y representing two character states).
48
a b
c
d e
Figure 6: Location of morphological measurements illustrated on (1a-1d) Hebertella alveata , USNM 87146 and (1e) Hebertella frankfortensis , USNM 258467. a, dorsal view, x 2.3; b, ventral view, x 2.3; c, anterior (dorsal valve up) view, x 2.3; d, lateral (dorsal valve up) view; e, ventral interior. Abbreviations: dh, height of the dorsal valve; du, dorsal umbonal angle; hl, hinge length; l, length of valve; sd, depth of sulcus; th, total height; vh, height of ventral valve; vml, length of ventral muscle scar field; vmw, width of ventral muscle scar field; vu, ventral umbonal angle; w, maximum width.
49 Characters Analyzed
The location of morphological measurements follows that illustrated in Figure 6.
The presumed primitive character state is coded as 0, while derived states are coded as 1 or 2.
1. Size. Determined by measuring the maximum shell width parallel to the hinge
line: (0), large ( ≥ 28.6 mm); (1), medium (20.0 ≤ x ≤ 26.8 mm); (2), small ( ≤ 18.6
mm).
2. Outline shape: (0), subquadrate; (1), elliptical; (2), circular.
3. Relative shell height. The ratio of the total height of an articulated individual and
the maximum width, measured parallel to the hinge line: (0), low ( ≤ 0.478); (1),
high (0.494).
4. Length. Determined by measuring the maximum shell length perpendicular to the
hinge line: (0), large ( ≤ 19.0 mm); (1), small ( ≤ 18.09 mm).
5. Depth of the shell. Ratio of the maximum shell length, measured perpendicular to
the hinge line, and the maximum shell width, measured parallel to the hinge line.
6. Relative length of the hinge line. The ratio of the length of the hinge and the
maximum width, measured parallel to the hinge line: (0), long ( ≥ 0.810); (1),
short ( ≤ 0.794).
7. Lateral profile. The ratio of the ventral valve height, measured as the maximum
vertical height of the ventral valve perpendicular to the commissure plane and the
dorsal valve height, measured as the maximum vertical height of the ventral valve
perpendicular to the commissure plane: (0), subequal (0.575 ≤ x ≤ 0.780); (1),
dorsal convexity greater ( ≤ 0.504); (2), ventral convexity greater ( ≥ 0.835). 50 8. Termination of the cardinal extremities. (0), extended, corners are angular or
alate; (1), absent, corners are rounded.
9. Width of double adductor ridge.
10. Ventral costae count. The number of costae present across a 5 mm segment
parallel to the hinge line, 5 mm from the umbo: (0), many ( ≥ 12); (1),
intermediate (9 ≤ x ≤ 11); (2), few ( ≤ 7).
11. Shape of the ventral valve: (0), subrectangular; (1), elliptical.
12. Relative inflation of the ventral valve. The ratio of the maximum ventral valve
height, measured perpendicular to the commissural plane, and the maximum
width, measured parallel to the hinge line: (0), high ( ≥ 0.207); (1), low ( ≤ 0.184).
13. Height of the ventral interarea. Measured from the hinge line to the end of the
interarea, perpendicular to the hinge line: (0), large ( ≥ 4.9 mm); (1), small ( ≤ 4.34
mm).
14. Length of the ventral muscle scars. The ratio of the maximum length of the
ventral muscle field, measured perpendicular to the hinge line, and the maximum
valve width, measured parallel to the hinge line: (0), long ( ≥ 0.368); (1), short ( ≤
0.328).
15. Maximum width of the ventral muscle scars. The ratio of the maxium width of
the ventral muscle field, measured parallel to the hinge line, and the maximum
valve width, measured parallel to the hinge line: (0), narrow ( ≤ 0.302); (1), wide
(≥ 0.326). 51 16. Ventral umbonal angle. The angle observed between the two limbs of the umbo
when the ventral valve is lying on the commissural plane: (0), wide ( ≥ 120°); (1),
narrow ( ≤ 118°).
17. Depth of the sulcus. The ratio of the depth of the sulcus, measured as the vertical
distance between the commissure at the center of the sulcus and the commissure
at the break in the slope at the sides of the sulcus, and the shell thickness (total
height) of the articulated specimen: (0), deep ( ≤ 0.269); (1), shallow ( ≥ 0.237).
18. Number of costae in the sulcus. The total count of costae between the slope
breaks at both sides of the sulcus, measured at the commissure: (0), many ( ≥ 17);
(1), few ( ≤ 12).
19. Sulcus origination from beak. Ratio of the distance, measured perpendicular to
the hinge line, from the ventral umbo to the beginning of a perceptible concave
deflection in the ventral valve, and the maximum length of the valve, measured
perpendicular to the hinge line: (0), distal ( ≥ 0.458); (1), proximal ( ≤ 0.408).
20. Dorsal costae count. The number of costae present across a 5 mm segment
parallel to the hinge line, 5 mm from the umbo: (0), many ( ≥ 13); (1),
intermediate (10 ≤ x ≤ 12); (2), few ( ≤ 9).
21. Relative inflation of the dorsal valve. The ratio of the maximum dorsal valve
height, measured perpendicular to the commissural plane, and the maximum
width, measured parallel to the hinge line: (0), high ( ≥ 0.267); (1), low ( ≤ 0.255).
22. Height of the dorsal interarea. Measured from the hinge line to the end of the
interarea, perpendicular to the hinge line: (0), large ( ≥ 1.7 mm); (1), small ( ≤ 1.53
mm). 52
Table 4. Data range of morphometric characters of species analyzed (All measurements in millimeters)
1 3 4 5 6 7 9 12 13 14 15 17 19 21 22 D tennesseensis 16.63- 0.551 13.94 0.8 0.654- 0.979 0.077 0.246 2.9 0.447 0.327 0.167 0.536 0.251 ? 17.42 0.789 D. winchelli 16.13- 0.591 13.89- 0.820- 0.683- 0.918 0.142 0.255- 3.54 0.49 0.371 0.205 0.624 0.287 1.53 17.36 14.24 0.861 0.736 0.263 M. extensa 16.88- ? 12.89- 0.764- 0.816- ? ? 0.249 5.19 0.383 0.367 ? 0.508 0.277 2.11 20.41 15.71 0.77 0.962 H. sinuata prestonensis 44.76 ? 39.2 0.876 0.962 ? ? ? ? 0.301 0.302 ? ? 0.362 ?
H. alveata richmondensis 31.16 0.601 25.4 0.815 0.988 0.479 ? 0.182 4.34 ? ? 0.269 0.375 0.375 ?
H. frankfortensis 18.0- 0.472- 14.32- 0.749- 0.677- 0.711- 0.04 0.207 3.13 0.311 0.241 0.228- 0.333- 0.24 1.74 24.22 0.509 19.42 0.802 0.752 0.835 0.33 0.482 H. occidentalis montoyensis 18.46- ? 14.68- 0.795- 0.730- ? 0.087- 0.232 6.42- 0.404- 0.379 ? 0.502 0.267 1.38 33.49 27.25 0.814 0.943 0.093 6.82 0.438 H. borealis 16.32- 0.435- 12.62- 0.755- 0.724- 0.780- ? 0.160- 2.06- ? ? 0.338- 0.331- 0.181- 0.940- 21.58 0.55 1 17.44 0.938 0.792 0.928 0.235 2.9 0.403 0.409 0.254 1.18 H. alveata 26.76- 0.469- 15.82- 0.591- 0.983- 0.575- ? ? 6.10- ? ? 0.237 0.207- 0.216- ? 39.3 0.475 29.2 0.802 1.05 0.758 6.14 0.325 0.319 H. parksensis 21.42- 0.526- 15.36- 0.717- 0.763- 0.67 0.064 0.165- 2.30- 0.328 0.23 0.322- 0.325 0.310- 1.80- 26.72 0.632 21.38 0.81 0.865 0.23 4.9 0.362 0.384 2.18 H. bursa 28.86 0.283 24.32 0.843 0.762 0.609 ? 0.143 1.58 ? ? ? ? 0.087 ?
H. melonica 22.0- 0.52 19.92 0.672 0.810- 0.926 0.045 0.275 4.31 0.426 0.37 0.147 0.459 0.255 2.36 29.64 0.9 H. clermontensis 16.53- 0.381 13.3- 0.792- 0.756- 0.598 0.032 0.134- ? 0.329- 0.300- 0.112 ? 0.223 1.4 17.6 14.72 0.836 0.911 0.148 0.368 0.302 H. subjugata 26.73 0.534 18.09 0.677 0.775 0.623 ? 0.184 3.84 ? ? ? ? 0.295 ?
H. pervetus 11.13 0.519 8.89 0.799 0.778 0.95 ? 0.224 1.36 ? ? 0.168 0.518 0.235 ?
H. occidentalis 24.08- 0.494- 19.0- 0.786- 0.736- 0.503- ? 0.169- 4.15- ? ? 0.125- 0.408 0.284- ? 32.18 0.537 25.3 0.789 0.794 0.746 0.212 5.3 0.295 0.336 H. sinuata 25.42- 0.575- 19.25- 0.718- 0.900- 0.504- 0.053 0.134- 5.97- 0.314 0.278 0.223- 0.351- 0.279- 3.35 39.33 0.579 28.22 0.799 0.966 0.699 0.235 6.17 0.342 0.39 0.413 53 Table 5. Statistical separation of morphometric characters (Measurements in mm)
Character Mean S.D. Range (mean ± 1 S.D.) ANOVA 1. Maximum width (0) small 16.89 1.85 x ≤ 18.7 P < 0.001 (1) medium 24.04 2.64 21.4 ≤ x ≤ 26.7 (2) large 33.37 4.96 x ≥ 38.3 3. Relative shell height (0) high 0.551 0.039 x ≥ 0.512 P < 0.001 (1) low 0.428 0.073 x ≤ 0.501 4. Length (0) small 14.66 2.08 x ≤ 16.74 P < 0.001 (1) large 24.29 4.89 x ≥ 19.40 5. Depth of shell (0) high 0.82 0.039 x ≥ 0.781 P < 0.001 (1) low 0.727 0.051 x ≤ 0.778 6. Relative length of hinge (0) short 0.741 0.04 x ≤ 0.781 P < 0.001 (1) long 0.916 0.072 x ≥ 0.844 7. Lateral profile (2) dorsal convexity greater 0.495 0.014 x ≤ 0.509 P < 0.001 (1) subequal 0.677 0.073 0.604 ≤ x ≤ 0.750 (0) ventral convexity greater 0.918 0.046 x ≥ 0.964 9. Width of double adductor ridge (1) narrow 0.047 0.012 x ≤ 0.059 P < 0.001 (0) wide 0.1 0.029 x ≥ 0.071 10. Ventral costae count (2) few 6.83 0.41 x ≤ 7 P < 0.001 (1) intermediate 10.45 0.82 9 ≤ x ≤ 11 (0) many 14.33 2.66 x ≥ 12 12. Relative inflation of ventral valve (1) low 0.158 0.019 x ≤ 0.177 P < 0.001 (0) high 0.235 0.021 x ≥ 0.214 13. Height of ventral interarea (0) small 3.124 1.048 x ≤ 4.172 P < 0.001 (1) large 5.89 0.628 x ≥ 5.262 14. Length of ventral muscle scars (1) short 0.316 0.012 x ≤ 0.328 P < 0.001 (0) long 0.423 0.041 x ≥ 0.382 15. Max width of ventral muscle scars (0) wide 0.366 0.02 x ≥ 0.346 P < 0.001 (1) narrow 0.276 0.032 x ≤ 0.308 17. Depth of sulcus (0) shallow 0.179 0.046 x ≤ 0.225 P < 0.001 (1) deep 0.333 0.041 x ≥ 0.292 19. Sulcus origination (1) proximal 0.345 0.057 x ≤ 0.402 P < 0.001 (0) distal 0.518 0.053 x ≥ 0.465 21. Relative inflation of dorsal valve (0) low 0.221 0.05 x ≤ 0.271 P < 0.001 (1) high 0.33 0.044 x ≥ 0.286 22. Height of dorsal interarea (0) small 1.355 0.267 x ≤ 1.622 P < 0.001 (1) large 2.206 0.55 x ≥ 1.656 54
Table 6. Character state distribution for taxa analyzed
1 1 1 1 1 1 1 1 1 1 2 2 2 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
D. tennesseensis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D. winchelli 0 X 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 M. extensa 0 X ? 0 1 1 ? X ? 0 1 0 1 0 0 1 ? 0 0 ? 0 1 H. sinuata prestonensis 2 1 ? 1 0 1 ? 1 ? 1 ? ? ? 1 1 0 ? ? ? 1 1 ? H. alveata richmondensis 1 1 0 1 0 1 2 1 ? 1 ? 1 0 ? ? 0 1 0 1 1 1 ? H. frankfortensis X X 1 X X 0 1 0 1 1 0 0 0 1 1 0 X 1 X Y 0 1 H. borealis X X X 0 X 0 1 0 0 1 0 X 0 ? ? 1 1 1 1 1 0 0 H. alveata Y 1 1 X X 1 1 1 ? 1 1 ? 1 ? ? 0 0 0 1 1 X ? H. parksensis 1 X 0 X X X 1 0 1 0 1 X 0 1 1 X 1 0 1 0 1 1 H. bursa 1 0 1 1 0 0 1 0 ? ? 0 1 0 ? ? ? ? ? ? 0 0 ? H. melonica 1 0 0 1 1 1 0 0 1 ? 0 0 0 0 0 1 0 0 0 0 0 1 H. clermontensis 0 X 1 0 0 X 1 0 1 Y X 1 ? 0 1 1 0 1 ? 2 0 0 H. subjugata 1 1 0 1 1 0 1 0 ? ? ? 1 0 ? ? 1 ? ? ? 1 1 ? H. pervetus 0 0 0 0 0 0 0 0 ? 0 0 0 0 ? ? 1 0 0 0 1 0 ? H. occidentalis 1 1 X 1 0 0 Y 1 ? 2 X X X ? ? 1 X X 1 2 1 ? H. sinuata Y 1 0 1 X 1 Y X 1 2 1 X 1 1 1 1 X 0 1 2 1 1
Missing data indicated by '?'. Character states listed as X and Y are polymorphic, where X=(0 & 1) and Y=(1 & 2) Character numbers are listed across the top of the table
55
Parsimony analysis
Character distributions were coded in MacClade 4.06 (Maddison and Maddison
2003) and imported into PAUP*4.0b10 (Swofford 2002) for parsimony analysis. The data set was subjected to a branch-and-bound search, in order to find the most parsimonious trees. All characters were treated as unordered and weighted equally.
Seventy-two most parsimonious trees with a length of 48 steps were produced.
The strict consensus tree is presented in Figure 6, and is used for the subsequent discussion herein. The consistency index (CI) for the recovered trees is 0.54 and the retention index (RI) is 0.70. The observed consistency index exceeds those derived from sets of random data of comparable size (CI = 0.32) at the 0.05 level of significance
(Klassen et al . 1991) indicating that the character set is informative.
The amount of support for the recovered cladogram was further characterized by jackknife analysis. By eliminating a set percentage of characters over numerous trials, information about the stability of branch positions is obtained (Felsenstein 1985;
Sanderson 1989). The jackknife analysis was performed in PAUP using the branch-and- bound search with 100,000 replicates and 10% deletion of characters (equivalent to two characters). Groups compatible with the single most parsimonious tree were retained.
The confidence values for the nodes obtained from the jackknife analysis are presented on the cladogram in Figure 6 and show strong support for the cladogram recovered in the analysis. 56
Support for the cladogram was further constrained by calculation of the g 1 statistic, a measure of the skewness of tree length distributions (Hillis and Huelsenbeck
1992). The g 1 value obtained from a distribution of 100,000 trees constructed from this data set is -0.513; a strong skew, significant at the p = 0.05 level (Hillis and Huelsenbeck
1992), indicating strong phylogenetic signal.
Figure 7: Single most parsimonious tree produced from analysis of character data presented in Table 3 using PAUP*4.0b10 (Swofford 2002). The nodes are numbered in circles and jackknife values are labeled in the internodes. Apomorphic characters that change unambiguously below nodes are listed in parentheses. Node 1, 5(0), 6(0), 20(1), 22(0); Node 2, 1(1), 4(0), 11(0), 13(0); Node 3, 3(0), 7(0), 10(1), 12(1), 18(1); Node 4, 17(0), 20(2); Node 5, 4(0), 22(0); Node 6, 2(0), 3(1), 11(0), 12(0), 18(0), 20(0), 21(0); Node 7, 5(0), 6(0), 8(1), 10(0), 20(0); Node 8, 1(0), 3(0), 7(1), 10(2), 16(0), 17(1), 20(2); Node 9, 6(1). 57
Results
Tree topology is mainly pectinate. A distinct division occurs between the outgroup taxa plus one ingroup taxon ( D. tennesseensis -H. pervetus ) and an ingroup defined by five unambiguous character state changes (Figure 7). The outgroup taxon
Mimella extensa Cooper forms a clade (node 2) with Hebertella melonica Shaler.
Hebertella pervetus Cooper ccupies a basal position while the remaining ingroup species form a reasonably well-resolved monophyletic assemblage. The three basal-most members branch in a pectinate pattern as follows: H. pervetus (node 3), H. clermontensis
Bradley (node 4) , and H. borealis Billings (node 5). The following two polytomies consisting of H. frankfortensis Foerste and H. bursa Raymond (node 6) and H. parksensis
Foerste and H. subjugata Hall (node 7) branch in a pectinate pattern. The remaining monophyly is characterized by a polytomy that includes H. sinuata prestonensis (Ladd)
H. alveata richmondensis Foerste 1910, and H. alveata Foerste. H. occidentalis Hall and
H. sinuata Hall form a clade (node 9).
Each of these clades is supported by specific character evidence. The monophyly of the Mimella clade consisting of M. extensa and H. melonica is supported by a high shell depth, short hinge, and short dorsal interarea (characters 5, 6, and 22; see Figure
3.3). Tree support for this branch is strong, as indicated by the jackknife value in Figure
3.2. Hebertella melonica forms a clade with the outgroup taxon Mimella extensa , indicating that H. melonica is actually a species of the genus Mimella .
The monophyly of the Hebertella clade, comprising the remaining ingroup species, is supported by the number of costae on the dorsal valve (character 20). 58
Hebertella pervetus , although separated from the outgroup taxa by one character trait
(character 20), is separated from the remainder of the Hebertella clade by five characters
(characters 3, 7, 10, 12, and 18). Hebertella pervetus may thus represent the primitive species of Hebertella . The placement of each taxon within the basal, pectinate portion of the Hebertella clade is supported by further evidence and by strong jackknife values
(Figure 3). The monophyly of members of Hebertella exclusive of H. pervetus is evidenced by increased shell height, high ventral convexity relative to the dorsal valve, an intermediate number of ventral costae, low ventral inflation, and high number of dorsal costae (characters 3, 7, 10, 12, and 18). A shallower sulcus supports the monophyly of taxa above H. clermontensis (character 17). Synapomorphies of shorter length and low inflation of the dorsal valve (characters 4 and 22) support the monophyly of taxa above H. borealis .
The remaining ingroup members of Hebertella are partially resolved. Two soft polytomies occur in a pectinate pattern. The first, shared by H. bursa and H. frankfortensis , occupies a basal position. Synapomorphies of subquadrate outline, low shell height, rectangular ventral valve, few dorsal costae, and high inflation of the dorsal valve (characters 2, 3, 11, 18, 21) support the monophyly of taxa above H. bursa and H. frankfortensis . A short hinge and alate cardinal extremities (characters 6 and 8) support the remaining clade above the polytomy of H. parksensis and H. subjugata.
Three unresolved taxa, H. sinuata prestonensis , H. alveata richmondensis , and H. alveata , form a polytomy at the basal position of the clade. A clade made up of H. occidentalis and H. sinuata are supported by few ventral and dorsal costae and large 59 umbonal angle (characters 10, 16, and 20). This clade is supported by a strong jackknife value (Fig. 7).
This analysis supports Walker’s (1982) synonymy of Hebertella occidentalis in part. Walker (1982) suggested that H. subjugata is a variant morphologic type of H. occidentalis . He noticed several distinguishing characteristics, the main one being much finer costae than those of H. occidentalis , but found that these differences were found in variations of H. occidentalis . Walker’s (1982) synonymy of H. subjugata with H. occidentalis ; however, is not supported by this study. In this analysis, H. subjugata is distinguished from H. occidentalis by six characters (characters 5, 6, 8, 10, 16, and 20; see Figure 3.3).
Evolutionary and biogeographic implications
The biogeographic history of this clade was driven by dispersal events related to the expansion or lateral shift of geographic range in response to cyclic events, such as sea level. Species of Hebertella were endemic to North American basins in the midcontinent
(Iowa, Wisconsin), as well as the East, including the Cincinnati Arch (Ohio, Kentucky,
Indiana) and Central Basin (Tennessee). Howe (1988) noticed strong affinities between the mixed fauna in the Central Basin with the faunas in the mid-continent as well as those of the Ohio Valley. The genus Hebertella was relatively unaffected by the Richmondian invaders in the Cincinnati Arch region, with speciation events and extinction occurring mainly in the Middle Ordovician.
60
Figure 8: Phylogenetic relationship of Hebertella with generalized biogeography.
From examining the cladogram in Figure 8, it is evident that Hebertella species were present ancestrally in the Midcontinent and Cincinnati Arch. The dominant speciation mode within this group is dispersal (traditional or geo-dispersal), which corresponds to the expansion and contraction of species ranges, as well as lateral tracking of a descendent species relative to its ancestor. Two episodes of vicariance are displayed in Figure 8; the contraction of the range of Mimella from the midcontinent into the
Cincinnati Arch, and the occurrence of early Hebertella species within the Midcontinent
(Wisconsin and Iowa). Hebertella pervetus and Hebertella clermontensis remain in the 61
Midcontinent through the Late Ordovician. Hebertella borealis , Hebertella bursa , and
Hebertella frankfortensis dispersed east, into the Nashville dome through the mid-
Ordovician. Hebertella frankfortensis is found in the Cincinnati Arch early in the
Cincinnatian, but does not last beyond the Fairview (C1 sequence). Specimens of
Hebertella borealis from Chazyan strata in Quebec were placed in Mimella by Cooper
(1956; Walker 1982) and were not included in this study. By node seven, there is a turnover from Hebertella dominance from the midcontinent, and persistence east into the
Cincinnati Arch. Hebertella subjugata is one of the earliest extrabasinal invaders into the
Cincinnati Arch during the Richmondian Invasion, but did not survive through the
Richmondian, possibly due to its restricted geographic range. Hebertella parksensis dispersed into the Nashville dome, and is found in the Lexington limestone. The stratigraphic ranges of Hebertella parksensis and Hebertella frankfortensis overlap within the Lexington limestone, which is stratigraphically below the Kope, but the two species are rarely found together (Walker 1982). Hebertella prestonensis dispersed back into the midcontinent (Iowa) during the Richmondian and is described in the Maquoketa formation (Ladd 1928).
Hebertella alveata and H. alveata richmondensis occur in the Liberty and
Whitewater of Indiana. Hebertella sinuata had flourished throughout the Cincinnati Arch and Tennessee during the entire Maysvillian-Richmondian transition. Due to an extensive range and general robustness, it was an ideal candidate for survival during the invasive regime and to the end of the Cincinnatian series.
62
Figure 9. 1, Mimella melonica (Hall 1847; MCZ 110011 (holotype), dorsal view), 1.0x. 2, Mimella melonica (Hall 1847; MCZ 110012 (hypotype), ventral interior view), 1.0x. 3, Hebertella occidentalis (Hall 1847; AMNH FI 030298 (lectotype), dorsal view), 1.0x. 4, Hebertella prestonensis (Hall 1847); USNM 71927, 1.0x; 4a, dorsal valve, 4b, ventral interior. 5, Hebertella frankfortensis Foerste, 1909; USNM 258476, 1.0x; 5a, dorsal valve, 5b, dorsal interior. 6, Hebertella frankfortensis Foerste, 1909; USNM 258467, 1.0x; 6a, ventral valve, 6b, ventral interior. 7, Hebertella parksensis Foerste, 1909; USNM 87055 (lectotype), 1.0x; 7a, dorsal valve, 7b, ventral valve. 8, Hebertella alveata Foerste, 1910; USNM 87146 (lectotype), 1.0x; 8a, dorsal valve, 8b, ventral valve.
63
Systematic Paleontology
Taxa and material examined that do not require detailed discussion or synonymy
The following specimens belong to the type series and were examined to determine character states for each species. Each of the species is considered to be a valid within the genus and neither taxonomic revision nor lectotype designation is required.
Diagnoses for these species can be determined by the original species descriptions cited below and character coding presented in Table 6.
Hebertella pervetus (Cooper 1930), AMNH 500278; H. clermontensis (Bradley 1921),
MCZ 110301, 110549, 110550; H. borealis (Billings), USNM 35402, 172148; H. bursa
(Raymond) MCZ 110282.
Order ORTHIDA Schuchert and Cooper, 1932
Superfamily ORTHACEA Woodward, 1852
Family PLECTORTHIDAE Schuchert and Levene, 1929
Genus MIMELLA Hall and Clarke, 1892
Mimella melonica (Willard 1928)
Figure 8, no. 1,2
Hebertella melonica Willard, 1928, p. 263, pl. 1, figs. 8-9.
Diagnosis.—[in Willard, B., 1928, Harvard Univ. Mus. Comp. Zoology Bull. V.6, n. 6a, p. 263]
Emended Diagnosis.— Shell medium in width (22-30 mm), long (20 mm); outline subelliptical. Lateral profile convexi-concave. Shell height high, depth low, dorsal valve 64 inflated. Hinge straight, cardinal extremities rounded or absent. Ventral valve elliptical; radial costae numerous, many within sulcus. Sulcus shallow, originating distally from umbo; umbo angle wide. Adductor scars long, wide; median double ridge rises to margin of scar field. Dorsal valve low; fold weak; interarea large.
Types. — Hebertella melonica, MCZ 110011 (Holotype); MCZ 110012 (Hypotype)
Occurrence.— Middle Ordovician, Ottossee Limestone, Virginia.
Discussion. — This species was originally designated to the genus Hebertella by Willard
(1928). Similar characters, such as height of the dorsal interarea, long hinge, and low depth places this species in a clade with the genus Mimella . This species, herein, will be regarded as Mimella melonica.
Genus HEBERTELLA Hall and Clarke, 1892
Hebertella occidentalis (Hall, 1847)
Figure 8, no. 3
Orthis occidentalis Hall, 1847, p. 127-128, pl. 32a, figs. 2a-m, pl. 32b, figs. 1a-I; Meek,
1873, p. 96, Pl. 9, fig. 3a-h.
Orthis sinuata Hall, 1847, p. 128-129, pl. 32b, figs. 2a-k, pl. 32c, figs. 2l-s; Hall and
Clarke, 1892, Pl. 5a, figs. 1-8; Caster, Dalve, and Pope, 1961, Pl. 4, figs. 2-4.
Hebertella latasulcata Foerste, 1914b, p. 131, pl. 3, figs. 7a, b.
Hebertella occidentalis Foerste, 1910, pl. 2, figs. 1,2; Wilson 1949; Caster, Dalve, and
Pope, 1961, Pl. 5, figs. 24, 25; Walker, 1982, p. 6-8, pl. 5, figs. 18-4; Davis, 1985;
Schwimmer and Sandy, 1996, p. 225, figs. 16-1.24-26; Howe 1988, p. 208, fig. 4.8-4.11. 65
Hebertella occidentalis sinuata . Schuchert and Cooper, 1932, Pl. 11, figs. 14, 17, 19, 20,
22-26.
Diagnosis.— Shells large or small, subelliptical or subquadrate; hinge line straight, narrower than greatest width; cardinal extremities rounded or angular; lateral profile convexo-concave or unequally biconvex; anterior commissure uniplicate. Ventral beak slightly incurved; dorsal beak arched over ventral interarea, umbo inflated; swollen tubulose costae. Delthyrial cavity deep; teeth strong, with lateral sockets; dental plates strong; umbonal cavities deep, muscle field obcordate, strongly impressed, bounded by an elevated ridge extending from the anterior ends of the dental plates; diductor scars subcrescentic, not enclosing the adductor track in front; adductor scars elongate suboval, borne on double median ridge with shallow groove in center; adjustor scars obscure at base and on sides of dental plates. Notothyrial cavity deep, branchiophores margining notothyrium, divergent, bluntly pointed, supported by convergent plates wwhich unite with the roof of the valve; socket deep, marked by small fulcral plate; cardinal process a thick ridge, median thickening extending to the center of valve; muscle marks obscure, posterior pair larger than anterior; radial lines from crural cavities.
Emended Diagnosis.— Shell medium to large (24-40 mm), long (19-29 mm); outline subquadrate to subelliptical, wider than long; maximum width between hinge and mid- length. Lateral profile convexo-concave or unequally biconvex. Shell height short, variable depth; ventral convexity greater or subequal to dorsal. Hinge straight, cardinal extremeties rounded or angular. Ventral valve variably inflated; few radial costae (within
5 mm window). Sulcus shallow to deep, originating proximal to umbo. Interarea mainly 66 large; umbo wide; adductor scars short and narrow, cordate; teeth prominent. Dorsal valve highly inflated; fold weak to strong.
Types.— Hall (1847) did not designate a holotype in the original description, but was figured previously by Hall (1847: pl. 5, fig. 18-41). A lectotype has not been designated subsequently, therefore, AMNH FI 030298 is here designated as the lectotype. This is a complete articulated specimen.
Other material examined.— Hebertella occidentalis Hall: AMNH 30298-30299
(syntypes); H. sinuata : ANSP 38106 (syntype).
Occurrence.— This species is common in Cincinnatian strata (Maysvillian-Richmondian) around Cincinnati, Ohio. Walker (1982) found it to be present in all Cincinnatian formations that overly the Lexington Limestone in Kentucky. Howe (1988) reports this species to be common in Richmondian strata in the Central Basin of Tennessee.
Discussion.— Hall (1847) originally defined H. occidentalis and H. sinuata as separate species in his Palaeontology of New York . Hall noted the occurrence of the two species within the same beds, and also the gradation of intermediate forms between the typical forms. Foerste (1910) noted the gradation in collections from the Maysville, KY section, noting that all intermediate stages may be found in the same location. Walker (1982) concluded that all specimens of the two species belong to a single variable species, H. occidentalis. Comparison of the character coding for these two forms reveals variation between the two species, however the strict consensus indicates that they are identical in all but one character, hinge length. The two forms are herein regarded as synonymous, 67 with the designated name H. occidentalis , since the name has page priority (Hall 1847).
This agrees with Walker’s (1982) synonymy of these taxa.
Hebertella prestonensis (Ladd, 1928)
Figure 8, no. 4a,b
Hebertella sinuata prestonensis Ladd, 1929, p. 401
Diagnosis.—Shells large, gibbous, subquadrate in outline, wider than long. Ventral valve much less convex than dorsal; deepest in umbonal area, which lies close to posterior margin. Broad and deep median sinus. Beak sharp, terminating a high cardinal area.
Dorsal valve highly convex, deepest at midpoint. Low broad median elevation arises in anterior third of valve. Cardinal extremities strongly reflexed, beak inconspicuous, cardinal area low, strongly curved. Surface of valves marked by coarse, bifurcating striae.
Concentric growth lines anteriorally prominent.
Emended Diagnosis.— Shell large (45 mm), protuberant, long; outline subquadrate, wider than long. Dorsal valve highly convex, deep sulcus, wide sulcus with few (10) coarse costae, costae bifurcate mid-valve. Adductor scar short, narrow.
Types.— Cotype B No. 71927, U.S. National Museum. Cotype B contains no ventral valve, however, the interior muscle field is visible and measurable. Cotype A is No. 6-
6503, State University of Iowa (not analyzed).
Occurrence.— Characteristic of the Cornulites Zone, Maquoketa shale of Iowa. Ladd
(1929) specifies that specimens from the Southeast Area are larger and more coarsely striated than those from the Northwest Area. 68
Discussion.— Ladd (1929) by original designation assigns the name Hebertella sinuata prestonensis to these specimens. This species is not a subspecies of H. occidentalis because of size, costae count, and umbo angle. The species name Hebertella sinuata Hall is no longer valid, for it has been synonymized with Hebertella occidentalis . The species shall be regarded, herein, as Hebertella prestonensis .
Hebertella parksensis Foerste, 1909
Figure 8, no. 7a,b
Hebertella maria-parksensis Foerste, 1909b, p. 319, pl. 7, figs. 6a, b.
Hebertella parksensis Walker, 1982, p. 8-9, pl. 5, figs. 1-17.
Diagnosis.— Shell medium (21-27 mm), length variably short to large (15-22 mm); outline subrounded; lateral profile subequal; cardinal extremities rounded to alate. Many uniform, closely spaced, extensive bifurcaton. Ventral valve elliptical; posteriorally convex to anteriorally flat; low to high inflation; interarea small; umbo wide. Adductor scar field short, narrow; elevated rim; double ridge elevated. Sulcus pronounced, begins proximal to erect beaks, distal to suberect beaks. Inflated dorsal valve; interarea large, strongly curved.
Types.— USNM 87055a-b (cotypes), USNM 258482, USNM 258481 (plesiotype).
Foerste (1909) did not designate a holotype in the original description. A lectotype has not later been designated, therefore USNM 87055a is here designated as the lectotype.
Occurrence.— Confined to the upper part of the Lexington Limestone and to parts of the
Clays Ferry Formation and the Point Pleasant Formation in Kentucky. 69
Hebertella subjugata Hall, 1847
Figure 8, no. 7a,b
Hebertella subjugata (Hall 1847), p. 129, pl. 32C, figs. 1 a-i,k,m,n
Diagnosis.— Medium shell size (26 mm), outline elliptical, wider than long, low depth, lateral profile subequal; dorsal valve highly convex. Hinge short, straight; cardinal extremities rounded. Ventral valve low; beak projecting beyond hinge; interarea long, slightly curved. Sulcus deep at anterior margin. Dorsal valve inflated; intermediate costae count (within 5mm window).
Types.— AMNH 30290 (Syntype)
Occurrence.— Confined to the upper part of the Lexington Limestone and to parts of the
Clays Ferry Formation and the Point Pleasant Formation in Kentucky.
Discussion. — Hall (1847) believed that H. sinuata, H. occidentalis, and H. subjugata were similar, with a distinguishing character being much finer costellae. With only one distinguishing character, Walker (1982) placed H. subjugata in synonymy with H. occidentalis and H. sinuata. Here, I place H. subjugata as an individual species due to at least seven characters, including costae count, hinge length, angle of umbo, and shell depth.
70
Chapter 4: Conclusions
The second chapter of this thesis discusses the utilization of Geographic
Information Systems methods in order to reconstruct the spatial and temporal distribution of articulate brachiopod species in the type-Cincinnatian of Laurentian North America.
The procedure demonstrated the ability of the user to use GIS to reconstruct species geographic range polygons from large amounts of collection data acquired from museums. The GIS database was also able to accept field data acquired after an initial analysis, demonstrating the ability of information technology to analyze data as it is altered within the database. This feature alone provides a valuable asset to paleontologists that work with large amounts of collection data, however, the GIS was only used as a tool for illustrating species range polygons. Range polygons representing species ranges within individual time slices, depositional sequences (Holland 1993), were digitized by hand in order to present a user optimized representation of range.
With the database constructed and species range polygons illustrated, several hypotheses were formed and tested. Analysis of the range reconstructions revealed changes in the size of polygons through time, as well as lateral translations. By quantifying range polygons, area values were statistically tested against calculated environmental variables, such as sea level.
Analysis of variance was conducted between the calculated area polygon values and values obtained from a sequence based water depth curve of the Cincinnati Arch
(Holland 1993). It was hypothesized that sea level fluctuations had a direct influence on 71 the size of a species’ range. With marginal significance, water depth within the
Cincinnati Arch affected the size of a species range.
By choosing a study interval that crosses a known major biotic invasion and subsequent extinction event, the study reveals valuable information about community structure during a major crisis interval. The Richmondian Invasion, characterized by wholesale influx of extrabasinal species into the Cincinnati Arch, is ideal for this study.
It is represented within a relatively complete succession of strata, both spatially and temporally, which allowed biogeographic patterns to be analyzed with minimal stratigraphic bias. Species ranges can be seen to enter the basin as well as disappear within time slices, suggesting stages of invasion, speciation, and extinction. It was hypothesized that species that have established large ranges before the invasion would preferentially survive the expansion of extrabasinal species. Combined Student t-tests revealed a significant correlation between range size and species survival. It is discussed that species that have established a large range before extinction may have had a preadaptation to cope with competing species.
In addition to being useful for statistical analyses, the GIS database provided a means of animating species ranges through time in order to identify and qualitatively discuss spatial patterns. Habitat tracking patterns are indicated by a lateral translation of a species range across the map through time. Situated on a gently trending ramp
(Holland 1993), species ranges move up and down the ramp, tracking a preferred environment as it moves in relation to sea level oscillations. 72
Modeled after the methods outlined in Rode and Lieberman (2004) for Middle to
Late Devonian brachiopods and bivalves, this project covers the Late Ordovician brachiopods of the Cincinnati Arch, and provides the means for further utilization of methods within other basins, and eventually a complex of basins. By establishing a means to study the dynamics of community structure through space, time, and across major episodes of biotic crisis, this project aims to provide a more conventional means to study the relationship between species range and the environment in both the past and present.
The third chapter of this thesis volume reveals a more detailed look at a particular genus, Hebertella , which played a role in the paleobiogeograhic study of the previous chapter. The genus, Hebertella , of North America was systematically revised using phylogenetic methods detailed in (Stigall Rode 2005). Thirteen species of Hebertella were included in this study, thus making it the most comprehensive revision of the genus to date. Type specimens for all included species were obtained from museums and 23 morphologic characters were coded, including detailed exterior characters of the valve, as well as several internal characters. The character data was analyzed using PAUP*4.0b10
(Swafford 2002), and a most parsimonious clade is presented in Figure 7.
Walker (1982) synonymized the species H. occidentalis and H. sinuata using conventional taxonomic methods, and in this study, this synonymy is confirmed by character state analysis. With preference given to the name H. occidentalis , the species name H. sinuata became void, thus removing it from H. prestonensis. Mimella
(Hebertella ) melonica was removed from the ingroup genus Hebertella and placed into 73 the outgroup genus Mimella . With a relatively resolved cladogram, ecological and biogeographic patterns are discussed. Having illustrated the biogeography of a few species in chapter 2, further patterns are discerned.
By establishing new paleontological methods and testing them on a diversity of taxa in different time periods and geographic locations, new biogeographic patters and evolutionary trends were be derived from existing fossil data. By using GIS methods within the Cincinnati Arch, geographic species range patterns were analyzed in both space and time. Analysis of these patterns provided insight into range expansion and contraction, habitat tracking, and mass extinction survival among a diverse assemblage of brachiopod species in a spatio-temperal aspect.
Phylogenetic analysis can be paired with paleobiogeography by adding an evolutionary element to the species whose ranges are displaying biogeographic patterns.
The revised systematics of the genus Hebertella , provides a cladogram in which not only evolution can be traced, but also biogeographic patterns associated with dispersal. It was found that the genus Hebertella originated in the Central Basin of Tennessee and dispersed into the Cincinnati Arch before the Late Ordovician. Species then dispersed into the Midwest during the Richmondian Invasion. Species that survived the
Richmondian Invasion within the Arch, such as H. occidentalis did so due to an expansion of geographic range before the invasion.
74
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Appendix 1: Cincinnatian Brachiopod Database
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Appendix 2: Geographic Area of Species Range Polygons
Genus Species Formation Sequence SL (std) Area (km2) Hebertella frankfortensis Fairview C1 100 981.87 Hebertella occidentalis-sinuata Fairview C1 100 1640.85 Platystrophia hopensis Fairview C1 100 290.07 Platystrophia laticosta Fairview C1 100 266.65 Platystrophia ponderosa Fairview C1 100 8075.08 Platystrophia sublaticosta Fairview C1 100 33.89 Platystrophia crassa Fairview C1 100 40.69 Plectorthis fissicosta Fairview C1 100 735.58 Plectorthis plicatella Fairview C1 100 158.69 Strophomena planoconvexa Fairview C1 100 57.29 Zygospira cincinnatiensis Fairview C1 100 101.85 Hebertella occidentalis Fairview C2 34 5053.79 Hebertella sinuata Mcmillan C2 34 3669.8 Onniella meeki Mcmillan C2 34 2164.3 Platystrophia laticosta Mcmillan C2 34 4136.04 Platystrophia ponderosa Mcmillan C2 34 9485.94 Platystrophia auburnensis Mcmillan C2 34 3340.15 Platystrophia clarksvillensis Mcmillan C2 34 1494.49 Platystrophia cypha Mcmillan C2 34 3821.83 Rafinesquina alternate Mcmillan C2 34 171.85 Rafinesquina fracta Mcmillan C2 34 944.95 Rafinesquina nasuta Mcmillan C2 34 203.22 Rafinesquina ponderosa Mcmillan C2 34 1526.07 Zygospira modesta Mcmillan C2 34 2030.67 Glyptorthis insculpta Arnheim C3 29 1264.19 Hebertella occidentalis Arnheim C3 29 656.646 Leptaena richmondensis Arnheim C3 29 2465.4 Onniella Meeki Arnheim C3 29 2325.84 Platystrophia ponderosa Arnheim C3 29 6574.67 Platystrophia clarksvillensis Arnheim C3 29 138.15 Platystrophia Cypha Arnheim C3 29 1029.83 Retrostriata Carleyi Arnheim C3 29 1554.52 Rhynchotrema Dentatum Arnheim C3 29 140.45 Zygospira Modesta Arnheim C3 29 1070.421 Catazyga headi Waynesville C4 62 3326 Glyptorthis insculpta Waynesville C4 62 2754.42 Hebertella occidentalis Waynesville C4 62 3467.62 Hebertella sinuata Waynesville C4 62 1605.13 Hebertella subjugata Waynesville C4 62 676.45 Lepidocyclus capax Waynesville C4 62 3706.34 Lepidocyclus perlamellosus Waynesville C4 62 2701.71 Onniella meeki Waynesville C4 62 4908.34
142
Genus species Formation Sequence SL (std) Area (km2) Platystrophia laticosta Waynesville C4 62 1655.77 Platystrophia ponderosa Waynesville C4 62 636.51 Platystrophia acultriata Waynesville C4 62 3116.76 Platystrophia annieana Waynesville C4 62 812.03 Platystrophia clarksvillensis Waynesville C4 62 2561.11 Platystrophia cummingsi Waynesville C4 62 323.1 Platystrophia cypha Waynesville C4 62 2260.69 Rafinesquina alternata Waynesville C4 62 5351.82 Rafinesquina ponderosa Waynesville C4 62 1785.92 Rafinesquina alternata-alternista Waynesville C4 62 417.18 Retrostriata carleyi Waynesville C4 62 1377.2 Rhynchotrema dentatum Waynesville C4 62 2883.11 Strophomena neglecta Waynesville C4 62 947.57 Strophomena planumbona Waynesville C4 62 1612.35 Strophomena sulcata Waynesville C4 62 3169.25 Strophomena nutans Waynesville C4 62 1649.24 Tetrapharella neglecta Waynesville C4 62 3924.39 Thaerodonta clarksvillensis Waynesville C4 62 674 Thaerodonta rugosus Waynesville C4 62 280.32 Zygospira modesta Waynesville C4 62 5220.77 Glyptorthis insculpta Liberty C4 62 2818.37 Hebertella occidentalis Liberty C4 62 2260.39 Hiscobeccus capax Liberty C4 62 446.383 Lepidocyclus capax Liberty C4 62 3777.66 Lepidocyclus perlamellosus Liberty C4 62 977.4 Leptaena richmondensis Liberty C4 62 957.72 Onniella meeki Liberty C4 62 3640.57 Plaesiomys subquadrata Liberty C4 62 2164.3 Platystrophia annieana Liberty C4 62 29.1 Platystrophia clarksvillensis Liberty C4 62 509.27 Platystrophia cypha Liberty C4 62 294.77 Rafinesquina alternata Liberty C4 62 466.07 Rafinesquina ponderosa Liberty C4 62 2468.28 Strophomena planumbona Liberty C4 62 1003.61 Thaerodonta clarksvillensis Liberty C4 62 1160.06 Thaerodonta rugosus Liberty C4 62 137.72
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