Sci Nat (2015) 102: 63 DOI 10.1007/s00114-015-1312-5

ORIGINAL PAPER

A new Ordovician arthropod from the Winneshiek Lagerstätte of Iowa (USA) reveals the ground plan of eurypterids and chasmataspidids

James C. Lamsdell1 & Derek E. G. Briggs 1,2 & Huaibao P. Liu3 & Brian J. Witzke4 & Robert M. McKay3

Received: 23 June 2015 /Revised: 1 September 2015 /Accepted: 4 September 2015 /Published online: 21 September 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract Euchelicerates were a major component of xiphosurid horseshoe crabs, and by extension the paraphyly of Palaeozoic faunas, but their basal relationships are uncertain: Xiphosura. The new taxon reveals the ground pattern of it has been suggested that Xiphosura—xiphosurids (horseshoe Dekatriata and provides evidence of character polarity in crabs) and similar Palaeozoic forms, the synziphosurines— chasmataspidids and eurypterids. The Winneshiek may not represent a natural group. Basal euchelicerates are Lagerstätte thus represents an important palaeontological win- rare in the fossil record, however, particularly during the initial dow into early chelicerate evolution. Ordovician radiation of the group. Here, we describe Winneshiekia youngae gen. et sp. nov., a euchelicerate from Keywords Dekatriata . Ground pattern . Microtergite . the Middle Ordovician (Darriwilian) Winneshiek Lagerstätte Phylogeny . Synziphosurine . Tagmosis of Iowa, USA. Winneshiekia shares features with both xiphosurans (a large, semicircular carapace and ophthalmic ridges) and dekatriatan euchelicerates such as Introduction chasmataspidids and eurypterids (an opisthosoma of 13 ter- gites). Phylogenetic analysis resolves Winneshiekia at the base Euchelicerates, represented today by xiphosurids (horseshoe of Dekatriata, as sister taxon to a clade comprising crabs) and arachnids (scorpions, spiders, ticks, and their rela- chasmataspidids, eurypterids, arachnids, and Houia. tives), comprise chelicerates (arthropods with cheliform Winneshiekia provides further support for the polyphyly of deutocerebral appendages) with a cephalic tagma of six ap- synziphosurines, traditionally considered the stem lineage to pendages united beneath a dorsal carapace (Weygoldt and Paulus 1979). During the Palaeozoic, four major lineages of Communicated by: Sven Thatje euchelicerate were present: xiphosurids, eurypterids, arach- nids, and the rare chasmataspidids (Dunlop 2010). During this Electronic supplementary material The online version of this article (doi:10.1007/s00114-015-1312-5) contains supplementary material, time, euchelicerates were major components of both aquatic which is available to authorized users. and terrestrial faunas and some groups occupied the role of apex predators (Lamsdell and Braddy 2010). The earliest con- * James C. Lamsdell firmed euchelicerates are xiphosurids from the Lower [email protected] Ordovician (Tremadocian) of Morocco (Van Roy et al. 2010) while potential chasmataspidid specimens from the late 1 Department of Geology and Geophysics, Yale University, 210 Cambrian (Dresbachian) of Texas await description (Dunlop Whitney Avenue, New Haven, CT 06511, USA et al. 2004). There is a large gap in the fossil record between 2 Yale Peabody Museum of Natural History, Yale University, New the Tremadocian occurrences and the major radiation of the Haven, CT 06511, USA four euchelicerate clades in the Silurian, occupied by fewer 3 Iowa Geological Survey, IIHR-Hydroscience and Engineering, than ten eurypterid species (Lamsdell et al. 2013a), a University of Iowa, 340 Trowbridge Hall, Iowa City, IA 52242, USA xiphosurid species from the Airport Cove locality (Katian) 4 Department of Earth and Environmental Sciences, University of of Manitoba, Canada (Rudkin et al. 2008), and a Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, USA chasmataspidid species from Sevier County (Middle 63 Page 2 of 8 Sci Nat (2015) 102: 63

Ordovician) of Tennessee, USA (Dunlop et al. 2004). locality on the Upper Iowa River near Decorah, but only the Furthermore, until recently, there were no convincing stem upper 4 m has been systematically collected due to the limited lineage taxa for any of these clades; the affinities of the sup- thickness accessible. The Winneshiek Shale is confined to the posed proto-eurypterid Kodymirus have been shown to lie Decorah Impact Structure, a circular basin about 5.6 km in with artiopods (Lamsdell et al. 2013b), and the phylogenetic diameter in the Decorah area which is interpreted to be the position of potential stem Barachnomorph^ taxa such as result of a meteorite impact (Liu et al. 2009; McKay et al. strabopids is equivocal (Tetlie and Moore 2004). This 2011). Palaeogeographic and palaeoenvironmental studies in- changed, however, with a revision of the Xiphosura. dicate that the crater was located in marginal to nearshore Morphological reappraisal and cladistic analysis of marine conditions (Liu et al. 2007, 2009;Witzkeetal. Palaeozoic synziphosurines—Bhorseshoe crabs^ with freely 2011). The fauna is dramatically different from a normal ma- articulating opisthosomal tergites—suggested that they repre- rine shelly fossil fauna, indicating a restricted environment sent a polyphyletic grouping of crown and stem inhospitable to typical marine taxa (Liu et al. 2006, 2007, Euchelicerates (Lamsdell 2013) rather than the stem lineage 2009). to Xiphosurida as previously supposed (Anderson and Selden The specimens described here were collected from two 1997). This new interpretation is supported by new discover- sources: blocks of shale eroded during flooding (labeled ies (Selden et al. in press) and further phylogenetic analysis WL), and a 4-m section excavated from the riverbed (labeled (Garwood and Dunlop 2014), but this has not resolved the WS). The specimens are partially disarticulated individuals issue of Ordovician ghost ranges, as the majority of preserved with cuticle which survives as a brown organic film. synziphosurine taxa occur in the Silurian and Devonian, with The specimens are accessioned in the Paleontology the only Ordovician form known from the Tremadocian of Repository, Department of Earth and Environmental Fezouata (Van Roy et al. 2010). Sciences, University of Iowa (SUI). Specimen SUI 140290 Here, we describe a euchelicerate arthropod from the was photographed using a Leica DFC420 digital camera at- Middle Ordovician Winneshiek Lagerstätte of Iowa. The tached to a Leica MZ16 stereomicroscope, and SUI 140291, new taxon, Winneshiekia youngae gen. et sp. nov., possesses SUI 140289, and SUI 140288 were photographed using a 13 freely articulating opisthosomal segments, a count charac- Canon EOS 60D digital camera with a Canon EF-S 60 mm teristic of eurypterids and chasmataspidids, and a large, semi- f/2.8 Macro USM lens. All specimens were imaged dry and circular, vaulted carapace and ophthalmic ridges, features pre- under incandescent light. Image cropping and levelling was viously considered to unite synziphosurines and xiphosurids. carried out using Adobe Photoshop CS5, and interpretive This mix of characters suggests a phylogenetic position inter- drawings were prepared with Adobe Illustrator CS5, on a mediate between xiphosurids and the other euchelicerate MacBook Pro running OS X. clades. Winneshiekia fills a stratigraphic gap in the early euchelicerate fossil record and provides further support for the paraphyly of Xiphosura as traditionally defined. Results

Material and methods Systematic palaeontology

The specimens are from the Middle Ordovician (Darriwilian) Chelicerata Heymons, 1901 Winneshiek Lagerstätte of northeastern Iowa (Liu et al. 2006, Euchelicerata Weygoldt and Paulus, 1979 2009). They are part of an unusual fauna including well- Dekatriata Lamsdell, 2013 preserved conodonts (51 % of specimens), phyllocarids Winneshiekia youngae gen. et sp. nov. (Figs. 1, 2, 3,and4) (7.9 %), eurypterids (6.6 %), and other bivalved arthropods Etymology. The genus is named for the Winneshiek Shale, (1.6 %)—arthropods are the most important invertebrate the formation in which it is found. The species is named in group (Briggs et al. in press). Excavation of the Winneshiek honor of Jean N. Young (1933–2007), geologist at Luther Shale yielded over 5000 fossil specimens (n=5354) of which College, who played an important role in the discovery of only four represent the taxon under consideration here. the Winneshiek Shale. The Winneshiek Shale is a greenish brown to dark gray Stratigraphical range and distribution. Middle Ordovician laminated sandy shale 18 to 27 m thick (Wolter et al. 2011; (Darriwilian) Winneshiek Lagerstätte, Winneshiek Shale McKay et al. 2011) which overlies an unnamed stratigraphic Formation, Winneshiek County, IA, USA. unit of thick massive breccia. The Winneshiek Shale is Material. Holotype: SUI 140288 (part and counterpart), disconformably overlain by the St. Peter Sandstone (Liu partial carapace, and complete opisthosoma of tergites 1–13. et al. 2006, 2009). Borehole data indicate that the total thick- Paratypes: SUI 140289 (part and counterpart), SUI 140290, ness of the Winneshiek Shale is about 18 m at the outcrop SUI 140291. Sci Nat (2015) 102: 63 Page 3 of 8 63

Fig. 1 Winneshiekia youngae, SUI 140288 (holotype): a part, b counterpart, and c interpretive drawing. Solid lines represent morphological features, whereas dashed lines indicate broken margins. CA carapace, LE lateral eye, MO median ocelli, T1–T13 tergites 1–13, TE telson. Scale bars 2mm

Diagnosis. Euchelicerate with broad, vaulted carapace; is highlighted by a dark organic stain in SUI 140291. Paired ophthalmic ridge associated with lateral eye; 13 opisthosomal median ocelli are situated axially and anterior to the lateral tergites; first tergite expressed as a laterally reduced eyes (Figs. 1 and 3). A cardiac lobe is present in the posterior microtergite; tergites 2–8 with angular epimera; tergites 9– axial region of the carapace (Fig. 2). 13 lacking epimera; pair of elongate apodemal nodes located The tergites increase in length posteriorly in steps 1, 2, 3– centrally on at least tergites 2–7. 10, 11–12, and 13, and the opisthosoma widens to a maximum Description. The holotype (SUI 140288) shows that the at tergite 6, narrowing beyond (Fig. 1). The first opisthosomal body is made up of a prosoma and an opisthosoma of 13 tergite is a microtergite, laterally reduced and lacking epimera tergites, the latter divided into a preabdomen (1–8) and (Figs. 1 and 2). A paired set of circular, dark stains located postabdomen (9–13) (Fig. 1). The appendages are not pre- centrally on the microtergite of SUI 140291 (Fig. 4)may served. The complete outline of the carapace is unknown but represent the insertion points for the underlying appendage SUI 140289 indicates a subsemicircular outline, vaulted, with (most likely VII based on its position underlying the first broad pleural regions (Fig. 2). This is reflected in SUI 140290 tergite following the prosoma, which bears six appendage (Fig. 3) although the carapace of that specimen is pairs in euchelicerates). The tergites of the preabdomen termi- foreshortened through compaction. nate laterally in angular epimera (Figs. 1 and 2). The tergites A lateral eye, crescentic in outline, is located centrimesially making up the postabdomen lack epimera. An articulating and associated with an ophthalmic ridge (Figs. 1, 2,and3). It facet extends across the anterior margin of each tergite

Fig. 2 Winneshiekia youngae, SUI 140289 (paratype): a part, b counterpart, and c interpretive drawing. AN apodemal nodes, CL cardiac lobe, OR ophthalmic ridge; other symbols and scale as in Fig. 1 63 Page 4 of 8 Sci Nat (2015) 102: 63

Fig. 3 Winneshiekia youngae, SUI 140290 (paratype): a specimen, with inset boxes showing the cuticular ornament, and b interpretive drawing. The position of the inset boxes is shown in gray. Symbols and scale as in Fig. 1; scale bars of inset boxes 0.5 mm

(Figs. 1 and 2). Paired elongate apodemal nodes are located those in SUI 140288, indicating that this specimen may have axially on tergites 2–7 (Fig. 2). A dark axial stain on SUI been more than 60 mm long. 140291 may represent the position of the gut. SUI 140290 Remarks. Winneshiekia youngae superficially resembles preserves cuticular ornamentation on the carapace and tergites members of the Cambrian–Ordovician aglaspidid comprised of small, closely spaced tubercles resulting in a fine arthropods (Van Roy 2006), but can be separated from them granulation (Fig. 3) which is also evident in places on SUI based on its possession of dorsal median ocelli, the lack of a 140291. mineralized exoskeleton, and a trunk with more than eleven None of the specimens are complete. The proximal portion tergites. Winneshiekia can also be separated from eurypterids of the telson is evident in SUI 140288 but its overall morphol- based on its visible microtergite, along with the presence of ogy is not preserved. The maximum preserved length of the ophthalmic ridges and a large carapace with a broad lateral most complete specimen SUI 140288 (Fig. 1), which lacks all field and expanded genal regions. The microtergite of euryp- but the most proximal part of the telson, is 31 mm, and the terids is strongly reduced and either lost or subsumed beneath maximum preserved width, at tergite 6, is 15 mm. The dimen- the carapace (Dunlop and Webster 1999;Haugetal.2012) sions of the incomplete specimens SUI 140290 and SUI while the eurypterid carapace lacks ophthalmic ridges and ex- 140291 indicate that they were similar in size. The tergites hibits no lateral expansion or genal spines (Lamsdell 2011). of SUI 140289 (Fig. 2), however, are about twice as long as The occurrence of epimera on the preabdomen but not the postabdomen of W. youngae also distances it from eurypterids: this configuration is well known in bunodids (Lamsdell 2013) but is only encountered in the derived adelophthalmids among eurypterids (Tollerton 1989). Finally, the probable unfused na- ture of appendage VII would preclude Winneshiekia from an assignment within Eurypterida. Apart from their co-occurrence in the Winneshiek Shale, the evidence that these four specimens represent the same taxon is the similarity in the position and form of the lateral eyes and median ocelli, the microtergite, and the angular preabdominal epimera. It is not clear whether the specimens represent molts or carcasses; the dark organic staining in SUI 140291 (Fig. 4) may indicate the decay of soft tissues as sug- gested in other chelicerates (Poschmann et al. 2005;Lamsdell et al. 2009), indicating that this specimen is a carcass. SUI 140288 (Fig. 1), however, exhibits telescoping of tergites 9– 11, which has been shown in decay experiments on scorpions to occur in molts but never in carcasses (McCoy and Brandt 2009). The preservation of SUI 140289 and SUI 140290 (Figs. 2 and 3) allows either a molt or carcass interpretation, Fig. 4 Winneshiekia youngae, SUI 140291 (paratype): a specimen and b and it is not uncommon for arthropods to expire during interpretive drawing. Gray denotes the presence of dark organic staining. VII? possible insertion of appendage VII; other symbols and scale as in molting (Aiken 1969;Peebles1978; Higgins and Rankin Fig. 1 2001). However, the associated eurypterid specimens Sci Nat (2015) 102: 63 Page 5 of 8 63 represent molts (Liu et al. 2007;Lamsdelletal.2015) and this Discussion may apply to the specimens of Winneshiekia with the excep- tion of SUI 140291. The monophyly of Xiphosura, which includes the living horseshoe crabs (Xiphosurida), as well as a paraphyletic group Phylogenetic analysis of Palaeozoic forms, the synziphosurines, was based on four supposed synapomorphies: the presence of ophthalmic ridges, In order to determine the phylogenetic position of a cardiac lobe, the presence of an axial region in the Winneshiekia youngae, the new taxon was incorporated into opisthosoma, and a reduced pre-opercular segment (Dunlop the matrix of Selden et al. (in press), resulting in a matrix and Selden 1997). Lamsdell (2013) showed that these charac- comprising 215 characters coded for 105 taxa included in ters are general arthropod traits (in the case of the axial region Additional file 1: Online Resource 1. This matrix is also avail- of the opisthosoma) or at least occur in other euchelicerates (in able in the online MorphoBank database (O’Leary and the case of ophthalmic ridges, the cardiac lobe, and reduced Kaufman 2012) under the project code p2191 (accessible from pre-opercular segment), and his phylogenetic analysis showed http://morphobank.org/permalink/?P2191). In addition to the the Xiphosura to be paraphyletic, a conclusion supported in a inclusion of Winneshiekia, the coding of characters for subsequent phylogenetic analysis of chelicerates by Garwood Kasibelinurus amicorum Pickett, 1993 and Houia yueya and Dunlop (2014). The retention of biramous prosomal ap- (Lamsdell et al. 2013c) was modified. The opisthosomal ter- pendages in some synziphosurines (Sutton et al. 2002;Briggs gites of Kasibelinurus are now considered to be fused into a et al. 2012), and the occurrence of a metastoma in at least one thoracetron (Van Roy, personal communication). The BH- species (Selden et al. in press), lend further support to the shaped^ cardiac lobe in Houia is recognized as a taphonomic polyphyletic nature of the group: a monophyletic Xiphosura artifact caused by compression of the holotype carapace, and would require the loss of biramous appendages and indepen- the second tergite is partially reduced. dent development of a metastoma in both xiphosurans and The analysis was performed using TNT (Goloboff et al. dekatriatans. Winneshiekia combines familiar xiphosuran 2008) (made available with the sponsorship of the Willi characters—broad preabdominal tergopleurae, a large semi- Hennig Society) employing random addition sequences circular carapace, and ophthalmic ridges—with features char- followed by tree bisection-reconnection (TBR) branch acteristic of Dekatriata Lamsdell, 2013 (Chasmataspidida, swapping (the mult commandinTNT)with100,000rep- Eurypterida, and Arachnida), namely an opisthosoma com- etitions with all characters unordered and of equal weight. prising 13 tergites and reduced postabdominal epimera. Such Jackknife (Farris et al. 1996), bootstrap (Felsenstein a combination is consistent with a paraphyletic or polyphyletic 1985), and Bremer (Bremer 1994) support values were Xiphosura. calculated in TNT, and the ensemble consistency, reten- Through its phylogenetic placement, Winneshiekia pro- tion, and rescaled consistency indices were calculated in vides important information on the ground pattern of Mesquite 3.02 (Maddison and Maddison 2015). Dekatriata and character polarity among chasmataspidids, eu- Bootstrapping was performed with 50 % resampling for rypterids, and arachnids. The morphology of Winneshiekia 1000 repetitions, while jackknifing was performed using confirms that an opisthosoma of 13 segments, which is simple addition sequence and tree bisection-reconnection retained in chasmataspidids (Dunlop 2002; Dunlop et al. branch swapping for 1000 repetitions with 33 % character 2004), is the plesiomorphic condition for the clade. The dorsal deletion. The analysis resulted in six most parsimonious expression of the first tergite (the microtergite in trees with a tree length of 659 steps, an ensemble consis- Winneshiekia) is therefore suppressed in eurypterids and tency index of 0.476, an ensemble retention index of arachnids. It has been suggested that a poorly sclerotized ter- 0.836, and a rescaled consistency index of 0.398. With gite is subsumed under the carapace in eurypterids (Dunlop its 13 opisthosomal tergites, Winneshiekia resolves at the and Webster 1999), although some authors consider this struc- base of the Dekatriata in the strict consensus tree (Fig. 5), ture to be a sclerotized region of arthrodial membrane between forming the immediate sister taxon to a clade comprising the anterior tergite and the carapace (Haug et al. 2012). chasmataspidids, eurypterids, arachnids, and Houia.This Irrespective of whether the eurypterid Bmicrotergite^ is a true latter clade is considered equivalent to the Metastomata – tergite or a secondarily thickened region of integument, how- euchelicerates with the seventh appendage pair fused into ever, basal eurypterids exhibit 13 somites ventrally (Lamsdell asingleplate—of Weygoldt and Paulus (1979). The con- 2011). In addition, scorpion embryos have been shown to sensus tree differs from that of Selden et al. (in press) possess 13 opisthosomal somites (Brauer 1895;Farley only in the position of Houia , which here resolves higher 2001). The presence of a freely articulating microtergite lack- in the cladogram, at the base of Metastomata, as sister ing pleurae in chasmataspidids (Marshall et al. 2014)reflects taxon to the last common ancestor of chasmataspidids, the plesiomorphic condition. On the other hand, the division eurypterids, and arachnids. of the chasmataspidid opisthosoma into a microtergite, three 63 Page 6 of 8 Sci Nat (2015) 102: 63 530 520 510 500 490 480 470 460 450 440 430 420 410 400 390 380 370 360 350 340 330 320 310 300 290 280 270 260 250 Fig. 5 Strict consensus tree of the six most parsimonious trees Cambrian Ordovician Silurian Devonian Carboniferous Permian retrieved from the phylogenetic S3S2 S4 S5 Dr FuroG Tre Flo DDar Sa Kat Llandov WL Lo P Ems Ei Gi Fras Famenn Tourna Visean Ser Ba Mo A Sak Art KCWuCh

analysis. Major clades that are not Arachnida Dekatriata the focus of the study Eurypterida (Antennulata, Megacheira, Chasmataspidida Pycnogonida, Xiphosurida, Houia yueya Chasmataspidida, Arachnida, and Winneshiekia youngae Eurypterida) do not vary in Willwerathia laticeps topology from Selden et al. (in Bembicosoma pomphicus press) and have been collapsed for Pasternakevia podolica ease of visualization. Taxon Limuloides limuloides ranges are mapped to the geologic Bunodes lunula ‘Xiphosura’ timescale. A possible range Pseudoniscus roosevelti extension for chasmataspidids Cyamocephalus loganensis based on Cambrian fossils Kasibelinurus amoricum (Dunlop et al. 2004) is indicated Xiphosurida in gray. Winneshiekia youngae Legrandella lombardi gen. et. sp. nov. is shown in red. Venustulus waukeshaensis For the full consensus tree with Camanchia grovensis branch support measures, see Anderella parva Additional file 2: Online Weinbergina opitzi Resource 2 Dibasterium durgae Offacolus kingi Pycnogonida segment buckler and nine segment postabdomen is clearly Therefore, appendage pair VII in Winneshiekia was probably derived relative to the differentiation into a preabdomen of not fused to form a metastomal plate as in eurypterids and eight segments and a postabdomen of five segments in chasmataspidids. They are likely to have been incorporated Winneshiekia. This division is retained in eurypterids and functionally into the prosoma as this arrangement appears scorpions and suggests that eurypterids with a preabdomen early in the euchelicerate stem lineage (Sutton et al. 2002; and postabdomen of six segments each (Lamsdell 2011) — Moore et al. 2005; Briggs et al. 2012). namely megalograptids and some onychopterellids—exhibit Winneshiekia youngae gen. et sp. nov. represents a transi- an independently derived condition. tional euchelicerate morphology, resolving phylogenetically The microtergite of Winneshiekia is very similar to the at the base of Dekatriata (Lamsdell 2013), i.e., the clade in- laterally reduced preopercular tergite of the synziphosurines corporating chasmataspidids, eurypterids, and arachnids, as Bunodes (Lamsdell 2013)andWillwerathia (Anderson et al. the sister taxon to Metastomata (euchelicerates with a fused 1998), even if more strongly reduced (Fig. 2). The likely ho- metastomal plate – sensu Weygoldt and Paulus 1979). mology of these structures shows that the addition of segments Winneshiekia combines a number of characteristic xiphosuran during the transition from 11 segments in the opisthosoma of features—such as the possession of a broad semicircular car- bunodids to 13 in dekatriatans must have occurred in the pos- apace and ophthalmic ridges—with a pattern of opisthosomal terior region of the opisthosoma, as the first and second ter- tagmosis consistent with chasmataspidids, eurypterids, and gites at least can be shown to be directly homologous between scorpions. The new taxon provides support for taxa. Many arthropods develop new segments anterior of the synziphosurines being an unnatural group. This support is telson (Olesen 1999; Minelli et al. 2003; Fusco et al. 2004). In derived through its possession of a mixture of Bxiphosuran^ eurypterids, however, the three posterior postabdominal seg- (ophthalmic ridges, broad semicircular carapace, unfused ap- ments are differentiated by their greater length or posterior pendage VII) and dekatriatan (opisthosoma of 13 segments, margin ornament (Lamsdell 2011) and a similar differentiation postabdomen lacking epimera, partially reduced second in length is evident in Winneshiekia (Fig. 1). This may corre- opisthosomal tergite, opisthosomal width constant in first spond to the plesiomorphic euchelicerate three-segmented few segments) characteristics, demonstrating that the charac- postabdomen (Lamsdell 2013), suggesting that additional seg- ters used to define Xiphosura are present together with the ments may have inserted anterior to the existing postabdomen. majority of characters that define Dekatriata. With these new The paired circular structures associated with the data taken into account, phylogenetic analysis confirms the microtergite of SUI 140291 (Fig. 4) appear to represent the paraphyletic nature of Xiphosura (Lamsdell 2013). cross section of limb insertions, as shown elsewhere in Winneshiekia is one of the earliest described euchelicerates chasmataspidids (Tetlie and Braddy 2004), synziphosurines and fills a stratigraphic gap in the fossil record (Fig. 5), adding (Moore et al. 2011), and eurypterids (Lamsdell 2011). to our knowledge of early euchelicerate evolution. Sci Nat (2015) 102: 63 Page 7 of 8 63

Discoveries such as Winneshiekia illustrate the impact that Farley RD (2001) Development of segments and appendages in embryos fossil Lagerstätten can have on our knowledge of even rela- of the desert scorpion Paruroctonus mesaensis (Scorpiones: Vaejovidae). J Morphol 250:70–88 tively well-known groups such as euchelicerates. The Farrell ÚC, Martin MJ, Hagadorn JW, Whiteley T, Briggs DEG (2009) Winneshiek Lagerstätte represents an important window into Beyond Beecher’s Trilobite Bed: widespread pyritization of soft early chelicerate evolution and is one of the few Ordovican tissues in the Late Ordovician Taconic foreland basin. Geology 37: – Lagerstätten to occur in the Middle Ordovician, which 907 910 Farris JS, Albert VA, Källersjö M, Lipscomb D, Kluge AG (1996) witnessed the shift from a mixed Cambrian/Palaeozoic fauna Parsimony jackknifing outperforms neighbor-joining. 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