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A New Synziphosurine (Chelicerata: Xiphosura) from the Late Llandovery (Silurian) Waukesha Lagerstätte, Wisconsin, USA Author(s): Rachel A. Moore, Derek E. G. Briggs, Simon J. Braddy, Lyall I. Anderson, Donald G. Mikulic, Joanne Kluessendorf Source: Journal of Paleontology, Vol. 79, No. 2 (Mar., 2005), pp. 242-250 Published by: Paleontological Society Stable URL: http://www.jstor.org/stable/4094976 . Accessed: 20/08/2011 04:27
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http://www.jstor.org J. Paleont., 79(2), 2005, pp. 242-250 Copyright ? 2005, The Paleontological Society 0022-3360/05/0079-242$03.00
A NEW SYNZIPHOSURINE (CHELICERATA:XIPHOSURA) FROM THE LATE LLANDOVERY (SILURIAN) WAUKESHA LAGERSTATTE, WISCONSIN, USA RACHEL A. MOORE, DEREK E. G. BRIGGS,2 SIMON J. BRADDY,1 LYALL I. ANDERSON,3 DONALD G. MIKULIC,4 AND JOANNE KLUESSENDORF5 'Departmentof EarthSciences, Universityof Bristol,Wills MemorialBuilding, Queen's Road, Bristol BS8 1RJ,United Kingdom,
ABSTRACT-A new synziphosurine(Chelicerata:Xiphosura) is described from the Late Llandovery(Silurian) Konservat-Lagerstditte of Waukesha,Wisconsin, USA. Venustuluswaukeshaensis n.gen. and sp. is characterizedby a semicircularcarapace with a slightly procurvedposterior margin lacking genal spines and an opisthosomacomposed of 10 freely articulatingsegments, divided into a preabdomenof seven segments with blunt pleuraeand a postabdomenof three segments lacking pleurae.The tail spine is shortand styliform.This is the earliest known unequivocalsynziphosurine, extending their fossil recordfrom the Wenlockto the Llandovery, and only the second species to be describedwith prosomalappendages; the presenceof six pairs (a pair of cheliceraeand five pairsof walkinglegs) contrastswith the seven in the synziphosurineWeinbergina opitzi, but is comparableto the numberin modem horseshoe crabs. V. waukeshaensisn. gen. and sp. is not assignedto a family here pendinga widerrevision, but it bearsmost resemblanceto the Weinberginidae.
INTRODUCTION During the Aeronian-early Telychian, Burnt Bluff and older Silurian strata in the northern Basin were be- YNZIPHOSURINESARE basal members of the phylum Chelicer- Michigan uplifted, came and were to erosion and karstification S ata, which includes xiphosurans (horseshoe crabs), eurypter- emergent, subjected and Mikulic and ids, chasmataspids, arachnids (e.g., spiders and scorpions) and (Kluessendorf Mikulic, 1998; Kluessendorf, The southern of this karstified which has a possibly the pycnogonids (sea spiders) (Dunlop, 1999; Waloszek 1999). edge ridge, relief of more than 50 is as an and Dunlop, 2002). Chelicerates are characterized by a pair of regional m, expressed 8-m-high at Wisconsin and chelate preoral appendages and a body divided into two tagmata, paleoscarp Waukesha, (Kluessendorf Mikulic, features the prosoma and opisthosoma. The closest living relatives of the 1996, 1998). Epikarstic (e.g., kamenitzas, kluftkarren, broad and runnel on the in- synziphosurines are the xiphosurids, which are often described as scalloping, notching, troughs) scarp dicate formation on carbonate strata within a coastal living fossils due to their extreme morphological conservatism unvegetated under humid conditions with at least abundant since the Mississippian (Waterston, 1985; Siveter and Selden, setting seasonally rainfall and BBF strata that 1987). There are four extant species of xiphosuran, the best (Kluessendorf Mikulic, 1996, 1998). the here were in an intertidal as known being Limulus polyphemus (Linnaeus, 1758), which is onlap scarp deposited setting, indicated fenestral interference rill and wrin- found along the Atlantic coast of North America (Shuster, 1982). by porosity, ripples, kle and tidal channels and Mik- Synziphosurines form a paraphyletic stem group of xiphosurans marks, microkarst, (Kluessendorf the toe of the beneath the is a chert characterized by an opisthosoma composed of nine to 11 freely ulic, 1996). Along scarp, BBF, to m thick that formed as a soil articulating tergites (Anderson and Selden, 1997). They range conglomerate up 1 probably residuum and was reworked as a from the Silurian to the Upper Devonian and their paleogeograph- lag deposit during transgression and The BBF out ic range includes the USA, Europe, Australia, and South America (Kluessendorf Mikulic, 1996). wedges against the more laminated and it is (Dunlop and Selden, 1997). scarp, becoming finely argillaceous; absent north of Waukesha. The nonmineralized cuticle of chelicerates requires special con- The Waukesha biota occurs within a laminated mudstone ditions for preservation such as those that prevailed in the Kon- finely and dolomite the lowest 2 m of the Brandon servat-Lagerstaitteof Waukesha County, Wisconsin (Mikulic et al., overlying Bridge strata. Fossils are uncommon and scattered the 1985a, 1985b). Silurian are comparatively scarce in throughout layer, Lagerstitten but are more abundant in certain et the geological record (Kluessendorf, 1994; Briggs et al., 1996), bedding planes (Mikulic al., to a accumulation of so this locality also provides important data for reconstructing the 1985a). They appear represent taphonomic molts within a sediment on the diversity of Silurian organisms. primarily arthropod deposited trap and Preservation of the fauna In this paper, we describe a new synziphosurine from the Wau- scarp (Mikulic Kluessendorf, 2001). is related to conditions that occurred at the The kesha Lagerstaitte.Following a summary of the Waukesha biota scarp. presence limited bioturbation and absence of de- by Mikulic et al. (1985a, 1985b) and the discovery of new ma- of fine-scale lamination, terial from this site, the taxon is described in detail and assigned cay in the strata adjacent to the scarp suggest rapid deposition in to a new genus and species. an anoxic environment. The fossiliferous, dolomitized limestone beds containing the GEOLOGICAL SETTING AND ASSOCIATED FAUNA Waukesha biota are limited to only two localities in Wisconsin. The Waukesha biota occurs within the Brandon Bridge For- The biota is dominated by arthropods and includes trilobites (13 mation (late Telychian-early Sheinwoodian) which outcrops in the genera), phyllocarids and ostracods, the earliest reported repre- Milwaukee, Wisconsin area (Mikulic and Kluessendorf, 1998). sentative of the class Thylacocephala, and at least three arthropods The Brandon Bridge Formation (BBF) is typically a thinly bed- of uncertain affinity (Mikulic et al., 1985a, 1985b). In addition, ded, light-green to pinkish-gray argillaceous dolomite that uncon- at least four wormlike taxa have been discovered (Mikulic et al., formably overlies the Kankakee Dolomite or Burnt Bluff Group 1985a). The absence of shelly fossils such as brachiopods, mol- (Aeronian) (Mikulic and Kluessendorf, 1998) and grades upwards luscs, corals, bryozoans, and echinoderms, which are common into the Waukesha Dolomite (Mikulic et al., 1985a). organisms in other Silurian biotas, is noteworthy. Those shelly 242 MOORE ET AL.--A NEW LOWER SILURIAN SYNZIPHOSURINE 243
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FIGURE1-Venustulus waukeshaensisn. sp., Lower Llandovery,Waukesha, Wisconsin, USA, holotype,UW 4001/21, ventralview. 1, Cameralucida drawing; 2, photograph. Db = doublure, F = fracture, Ph = phosphatic material, P1 = pleura, Ri = ridges, Mr = median ridge, numbers 1-10 = opisthosomal segments. Scale bar = 1 mm.
fossils that are present are commonly decalcified. Also absent are PRESERVATION their occurrence at other Silurian eurypterids, despite arthropod- Of the eight specimens, three are almost complete and five rich such as the late Silurian Bertie Waterlime localities, (Pi•idolf) consist only of the prosoma and part of the opisthosoma. All of New York State and (Clarke Ruedemann, 1912; Kluessendorf, specimens are flattened dorsoventrally and in most cases splitting A new of has been 1994). genus dasycladalean algae recently occurred between the tergites and sternites. Preferential decay described from the Waukesha but occurs at a Lagerstditte separate around the margins has resulted in poorly preserved lateral re- level to those which the rest of the biota et yield (LoDuca al., gions in all specimens. In some cases, the carapace margin, the 2003). opisthosomal pleurae, and distal regions of the tail spine are ab- The entire BBF has been dated as late Wen- Llandovery-early sent. Localized conditions resulted in preferential preservation of lock based on conodonts and however the Waukesha graptolites, the carapace in some specimens (Fig. 2) and prosomal appendages from which V. waukeshaensis n. and is biota, gen. sp. derives, in others (Fig. 3). Where the carapace is preserved, a series of found within the celloni biozone dat- specifically Pterospathodus radiating ridges and furrows is evident in the interophthalmic area. ed as to mid based on conodont evidence early Telychian (Mikulic These features may be difficult to discern due to infilling and et al., 1985a, 1985b; Mikulic and Kluessendorf, 1998). compaction but, despite being superficially similar, are not inter- preted as appendage coxae due to the continuous nature of the MATERIALS AND METHODS cuticle. Where the prosomal appendages are preserved, the distal The material consists of eight specimens, five of which have regions are absent and the podomere boundaries are only evident counterparts. All are held at the Geology Museum, Department in the fifth pair of walking legs (Fig. 3). of Geology and Geophysics, University of Wisconsin, Madison, EDX analysis revealed that white material within the specimens USA under the catalog number UW 4001. is phosphatic in composition. The distribution of phosphate ap- Scanning Electron Microscope (SEM) and X-ray dispersive pears to be related to the position of prosomal appendages and (EDX) analyses were carried out using a Cambridge Instrument other muscle-rich areas, but SEM analysis failed to reveal any Stereoscan 250 MK3. Camera lucida drawings were prepared us- preserved muscle fibers. Irregular depressions of varying size and ing a WILD stereomicroscope with a drawing tube attachment. shape in the central regions of specimen UW 4001/22 (Fig. 2, Morphological terminology follows Selden and Siveter (1987). Mn) often contain a phosphatic infilling. We believe these to be The systematic classification used follows Anderson and Selden the result of mineralization on the surface rather than a reflection (1997). of carapace sculpture. 244 JOURNAL OF PALEONTOLOGY, V. 79, NO. 2, 2005
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SYSTEMATIC PALEONTOLOGY (see also Bartels et al., 1998) led them to disagree with Eldredge and that W. and L. lombardii have CHELICERATAHeymons, 1901 (1974) propose opitzi possibly Phylum 10 Their of W. Class XIPHOSURALatreille, 1802 only opisthosomal segments. assignment laticeps to the was based on an opisthosomal count of 10 are Weinberginidae Discussion.-Relationships among synziphosurines poorly among other characteristics. They acknowledged, however, that known and such as the number of diagnostic features, opistho- the opisthosomal segment count of L. lombardii required verifi- somal are obscure even in well-described taxa. The segments, cation and that further work on synziphosurine relationships was described here form of a specimens part larger project dealing needed (Anderson et al., 1998). For this reason assignment of V. with a of oth- synziphosurine relationships. Pending redescription waukeshaensis to the family Weinberginidae is not proposed here, er relevant material these are not to a specimens assigned higher despite the fact that it shares characters with both W. opitzi and taxon, although a brief discussion of their affinities follows. L. lombardii. V. waukeshaensis differs from W. in the clear division of Genus VENUSTULUSMoore new genus opitzi the trunk into a preabdomen and a postabdomen lacking distinct waukeshaensis new Type species.-Venustulus species. pleurae, although it is similar to the condition in L. lombardii. V. semicircular with Diagnosis.--Carapace slightly procurved waukeshaensis differs from both W. opitzi and L. lombardii in the area with four posterior margin, lacking genal spines. Ophthalmic presence of blunt pleurae (W. opitzi has rounded pleurae and L. of and furrows. axis wide pairs radiating ridges Opisthosomal lombardii has short lateral spines) and a concave posterior pro- relative to Clear division of into pleural regions. opisthosoma somal margin. In addition, V. waukeshaensis lacks the axial and of seven and of three preabdomen segments postabdomen seg- lateral-raised nodes of the opisthosoma of weinberginids and the ments. Preabdominal with blunt and directed segments posteriorly anterior median deflection in L. lombardii (Eldredge, 1974). V. First not reduced to a and second pleurae. tergite microtergite waukeshaensis has six pairs of appendages in the prosomal region not Postabdominal narrower and tergite hypertrophied. segments as opposed to seven in W. opitzi (Sttirmer and Bergstr6m, 1981; than Tail longer preabdominal segments, lacking pleurae. spine Moore et al., in press); appendages are unknown in L. lombardii styliform. and W. laticeps. Etymology.-Venustulus = charming (Latin). Occurrence.-Late Llandovery (early-mid Telychian), Lower VENUSTULUS WAUKESHAENSISMoore new species Silurian, Waukesha Lagerstditte,Wisconsin, USA. Figures 1-4; Table 1 n. and differs Discussion.-Venustulus waukeshaensis gen. sp. Xiphosure;MIKULIC ET AL., 1985a, p. 715-716, fig. 2a. from bunodid synziphosurines (Bunodes Eichwald, 1854; Limu- Xiphosure;MIKULIC ET AL., 1985b, p. 78, fig. 3, pl. 1, figs. 11, 12. loides Woodward, 1865; Pasternakevia Selden and Drygant, 1987) in lacking a hypertrophied second opisthosomal segment Diagnosis.-As for the genus. and from pseudoniscid synziphosurines (Pseudoniscus Niesz- Description.-The dorsal surface of the prosoma is covered by kowski, 1859; Cyamocephalus Currie, 1927) in lacking a spatu- a semicircular carapace with a slightly procurved posterior margin late-shaped carapace and genal cornua, and having a well defined (Fig. 1). Genal regions are angular but are not developed into pre/postabdominal boundary. The 10 opisthosomal segments ex- genal spines. Within the interophthalmic area of the carapace is clude V. waukeshaensis from the Kasibelinuridae, the most-de- a complex series of radiating ridges and broader furrows (Fig. 2). rived synziphosurine family, according to Anderson and Selden Four pairs of furrows (evident as ridges on specimen UW 4001/ (1997) based on the synapomorphy of nine opisthosomal tergites. la in ventral view) radiate from the medial region of the carapace The shape of the carapace, lack of a hypertrophied second seg- and extend towards the ophthalmic ridge, becoming slightly wider ment, and presence of 10 opisthosomal segments in Venustulus as they approach it. They flank a median furrow, which is poorly waukeshaensis bear most resemblance to the family Weinbergin- preserved. idae Richter and Richter, 1929 among synziphosurines. This fam- Six pairs of prosomal appendages are evident in specimen UW ily currently contains three monospecific genera (Anderson, 1996; 4001/9 (Fig. 3), the first of which are the chelicerae (I). These Anderson et al., 1998): Weinbergina opitzi Richter and Richter, are followed by five pairs of walking legs (II-VI). The append- 1929 and Willwerathia laticeps (Stormer, 1936; see also Anderson ages diverge radially from the central region of the prosoma and et al., 1998), both from the Lower Devonian of Germany, and are folded towards the posterior carapace margin. The chelicerae Legrandella lombardii Eldredge, 1974 from the Lower Devonian extend anteriomedially and are shorter and narrower than the of Bolivia. W. opitzi has 10 visible opisthosomal segments (Rich- walking legs (Fig. 3). Individual podomeres are only evident on ter and Richter, 1929; Sttirmer and Bergstrim, 1981) whereas appendage VI-on the right of the pair (on the part: Fig. 3.1, 3.2) Eldredge (1974) described L. lombardii as having 11, the first of and less clearly on the left of the pair (on the counterpart: Fig. which is a reduced articulating microtergite. Similarities between 3.3, 3.4). Appendage VI consists of at least six podomeres, but W. opitzi and L. lombardii, and the presence of an articulating the most distal is incomplete and poorly preserved. Where the microtergite in all other synziphosurines, led Eldredge (1974) to podomeres are complete distally each projects into a stout spine. suggest that W. opitzi possessed a microtergite hidden beneath the The opisthosoma consists of 10 freely articulating segments, prosomal margin. Sttirmer and Bergstrim (1981) redescribed W. divided into a preabdomen of seven and a postabdomen of three opitzi and concluded that although a microtergite is not evident, (Fig. 1). The axial region of the preabdomen is wide in relation it is likely to be present, a view accepted by Selden and Siveter to the pleural regions. The first tergite is slightly narrower than (1987) and Anderson and Selden (1997). the posterior margin of the prosoma. Each subsequent tergite of Further consideration of W. opitzi by Anderson et al. (1998) the preabdomen is approximately 10 percent narrower than the
FIGURE2-Venustulus waukeshaensisn. gen. and sp., Lower Llandovery,Waukesha, Wisconsin, U.S.A. 1, Cameralucida drawing;2, photograph, UW 4001/1a, ventralview of dorsalsurface; 3, Cameralucida drawing;4, photograph,UW 4001/lb, dorsalview of ventralsurface. F - fracture, P1 = pleura,Mn = roundedmineralized depressions, Ri = ridges (*furrowsin dorsalview), Fu = furrows(*ridges in dorsalview), numbers1- 10 = opisthosomalsegments. Stipple indicates phosphatized material. Scale bar - 5 mm. 246 JOURNAL OF PALEONTOLOGY, V. 79, NO. 2, 2005
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3 4 MOORE ET AL.-A NEW LOWER SILURIAN SYNZIPHOSURINE 247 one preceding it, resulting in tapering of the preabdomen poste- riorly. Specimen UW 4001/9 (Fig. 3) bears an oval-shaped struc- ture 3-4 mm wide in the center of the first opisthosomal tergite. This structure is not evident in any other specimens. Pleural re- gions of the preabdomen are quadrate, terminate bluntly, and are directed posteriolaterally (Figs. 1, 2.1). The segments of the post- abdomen lack pleurae and are narrower and longer than those of the preabdomen. Successive segments narrow gradually towards the tail spine, which inserts into the tenth tergite. The tail spine is short and styliform with a median ridge (Fig. 1). Only the central region of the tail spine is preserved in specimen UW 4001/ 1 (Fig. 2) and the apparent bifid termination of the tail spine in specimen UW 4001/9 is a preservational artifact (Fig. 3). Etymology.-Referring to Waukesha County, Wisconsin, from where the specimens were collected. Type.-Holotype, UW 4001/21, Geology Museum, Department FIGURE4-Dorsal reconstructionof Venustuluswaukeshaensis n. gen. of Geology and Geophysics, University of Wisconsin, Madison, and sp. USA. Other material examined.-UW 4001/la+b; UW 4001/9a+b, opitzi (Lehmann, 1956), Pseudoniscus aculeatus (Ruedemann, UW 4001/22a+b; UW 4001/23a+b; UW 4001/24a+b; UW 1916), and Bunodes lunula Eichwald, 1854. 4001/25; UW 4001/26, as above. repository The first opisthosomal tergite in synziphosurines (which is fre- Occurrence.-Late Telychian), Lower Llandovery (early-mid quently reduced to a microtergite) is believed to be homologous Silurian, Waukesha Wisconsin, USA. Lagerstditte, to the chilarial segment (somite VII) of L. polyphemus (Selden Discussion.-Both the and size of (Ta- preservation specimens and Siveter, 1987) which is incorporated into the prosoma in liv- ble 1) result in differences between them. Measurements of car- ing Xiphosura (Scholl, 1977). The timing of the incorporation of width and normalized for overall size, show apace length, body the chilarial segment into the prosoma of xiphosurans is unknown that the of the 1) is relative carapace holotype (Fig. slightly larger in their fossil record and has implications for the numbering of to the size of the opisthosoma than in the only other specimen but in the absence of evidence to the in the opisthosomal segments, with a complete carapace, UW 4001/1 (Fig. 2). Change the or first visible relative size of the most reflects dif- contrary, microtergite, opisthosomal segment, carapace likely ontogenetic is here recognized as segment one. Reduced first opisthosomal ferences, as the holotype is approximately 77 percent smaller than are evident in some B. lunula and UW 4001/1 and is a modern limulids segments synziphosurines (e.g., probably juvenile. Although L. and their has been inferred in others, do not show such a in size relative to total lombardii) presence e.g. change carapace body W. opitzi and 1981). It has been suggested (Shuster, 1982), studies of the of (Sttirmer Bergstrtim, length ontogeny eurypterids that a reduced first opisthosomal segment is a synapomorphy of have shown that the ratio of the of the carapace versus that length the Xiphosura (which includes the paraphyletic synziphosurines) of the does diminish with (Andrews et al., opisthosoma growth (Dunlop and Selden, 1997). There is no evidence of a reduced 1974). Eurypterids may provide a better model than modern first in V. waukeshaensis. limulids for in as the opisthosomal segment ontogenetic changes synziphosurines, opis- The walking legs in W. opitzi consist of eight podomeres thosomal tergites are fused in the latter. and terminate with an of on the Based on measurements of the relative to the car- (coxa-transtarsus) array spurs opisthosoma tibial, basitarsal, and telotarsal and in a width of 35.5 mm and segments (Sttirmer Bergstr6m, apace complete specimens carapace 1981; Moore et al., in These are believed to have of 23.0 mm is calculated for UW 4001/9. This press). spurs length suggests functioned as a "snow shoe" adaptation to living on soft sedi- that the prosomal appendages occupied less of the total carapace ment. The of V. waukeshaensis are area than in modern limulids but this nonetheless appendages poorly preserved appears plau- but the sixth (fifth walking leg) consisted of at least six podom- sible. We therefore interpret UW 4001/9 as a specimen of the eres. It is that more were as in W. same taxon. likely podomeres present, opitzi and L. There was a boundary The structure labeled in 3 has not been observed in polyphemus. probably podomere '?' Figure where the is bent at -45 degrees (Fig. 3.1, 3.3, VI). of V. waukeshaensis n. and or other appendage other specimens gen. sp. There is no evidence of on any of the podomeres but they Its in the first of the spurs synziphosurines. position segment opistho- to show a broad distal spine which is not evident in W. soma differs from that of the in modern li- appear reproductive organs opitzi or modern xiphosurans. The last podomere on the right side mulids or which are found on the eurypterids, opisthosomal gen- of UW 4001/9a (Fig. 3.1, VI) is incomplete and it is not known ital operculum and second opisthosomal segment, respectively. In whether or not it was chelate. The chelicerae are likewise incom- the in eu- any case, genitalia both limulids (Shuster, 1982) and plete and no chelate distal region is evident. rypterids (Stormer, 1973; Braddy and Dunlop, 1997) do not re- A dorsal reconstruction of Venustulus waukeshaensis is shown semble this structure in V. waukeshaensis. Its nature remains enig- in Figure 4. matic. ADDITIONAL SYNZIPHOSURINE Eyes are unknown in V. waukeshaensis. Among synziphosuri- AN nes, unequivocal lens structures have only been described in L. The Waukesha Lagerstaitte may contain a second new synzi- lombardii, although possible examples have been described in W. phosurine, but the preservation of the single specimen is too poor
FIGURE3-Venustulus waukeshaensisn. gen. and sp., Lower Llandovery,Waukesha, Wisconsin, U.S.A. 1, Cameralucida drawing;2, photograph, UW 4001/9a (mistakenlylisted as UW 4001/16 in Mikulic et al., 1985a, p. 80); 3, camera lucida drawing;4, photograph,U.W 4001/9b. F = fracture,T.sp = tail spine,? = enigmaticstructure, I-VI = prosomalappendages, numbers 1-10 = opisthosomalsegments. Scale bar = 5 mm. 248 JOURNAL OF PALEONTOLOGY, V. 79, NO. 2, 2005
TABLE1-Dimensions of the most complete specimens of Venustulus wau- SYNZIPHOSURINE ORIGINS keshaensis n. gen. and sp. (in millimeters). * denotes incomplete measure- ments. Venustulus waukeshaensis n. gen. and sp. is only the second synziphosurine to be described with prosomal appendages. W. op- Opistho- itzi is the best-known synziphosurine due to its remarkable pyri- Prosomal Prosomal somal Tail sp. tized of Hunsrtick Slate fossils, which allows number width preservation, typical Specimen length length length the study of x-radiographs of the specimens (Sttirmer and Bergs- U.W.4001/21 (holotype) 5.1 4.0 4.7 2.5 tr6m, 1981; Bartels et al., 1998). W. opitzi has seven pairs of U.W.4001/1 23.5 15.4 23.0 8.8* in the of chelicerae and six U.W.4001/9 22* 20.0* 36.5* 16.5* appendages prosomal region (one pair U.W.4001/27 18.6 17.7 21.4* pairs of walking legs) (Sttirmer and Bergstr6m, 1981). The sev- enth pair of appendages is believed to be homologous to the chi- laria of modem horseshoe crabs and to the eurypterid metastoma and scorpion sternum (Sttirmer and Bergstr6~m,1981; Selden and to allow it to be described and named (Fig. 5). It differs from V. Siveter, 1987; Dunlop and Webster, 1999). The presence of six waukeshaensis n. gen. and sp. in having a U-shaped, parallel- pairs of prosomal appendages in V. waukeshaensis indicates that sided carapace with a straight posterior margin. The opisthosoma not all synziphosurines shared a complement of seven appendage is parallel-sided, but the number of opisthosomal segments cannot pairs. The reduction of appendage seven in V. waukeshaensis, as be determined due to poor preservation. There were at least eight in the chilaria of modern limulids, may represent a more derived segments but there is a significant gap between the eighth segment form than W. opitzi. Chilaria are unknown in fossil xiphosurans, and the preserved portion of the tail spine, so the position of the even in exceptionally preserved limulids such as Alanops mag- opisthosoma/tail spine boundary cannot be determined. Segments nificus (Racheboeuf et al., 2002) from the Upper Carboniferous seven and eight are significantly longer than the preceding seg- of central France. ments and may represent the postabdomen. The tail spine appears Synziphosurine origins are poorly known. Lemoneites spp. to be long and styliform. The specimen is dorsoventrally flattened Flower, 1969 has often been cited as a possible Ordovician syn- on an uneven bedding surface which adds to the difficulty in ziphosurine (Anderson and Selden, 1997; Dunlop and Selden, interpretation. However, this form does bear some resemblance to 1997), but it is particularly problematic due to poor preservation the pseudoniscids. and doubtful characters. The aglaspidids were considered to be
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FIGURE5-Poorly preserved, possible synziphosurine, Lower Llandovery, of Waukesha, Wisconsin, USA. 1, Camera lucida drawing; 2, photograph, counterpart, UW 4001/27a. Ap? = possible appendages, P1 = pleura, numbers 1-8 = opisthosomal segments, Tsp = tail spine. Stipple indicates areas of mineralized cuticle. Scale bar = 5 mm. MOORE ET AL.-A NEW LOWER SILURIAN SYNZIPHOSURINE 249 the Cambrian sister group of Xiphosura (Stormer, 1955; Eldredge, DUNLOP,J. A. 1999. A review of chelicerateevolution. Boletin de la 26:255-272. 1974), but, since Briggs et al. (1979) removed them from Cheli- SociedadEntomol6gica Aragonesa, cerata their is uncertain. More recent cladistic DUNLOP,J. A., ANDP. A. SELDEN.1997. The early historyand phylogeny position analysis H. Thomas resolved them as sister to a the Hunsriick of the chelicerates,p. 221-235. In R. A. Fortey and R. group clade including & London. Cheloniellon + Chelicerata et (eds.), ArthropodRelationships. Chapman Hall, Slate arthropod (Wills al., 1998). DUNLOP,J. A., ANDM. WEBSTER.1999. Fossil evidence,terrestrialization Cyamocephalus loganensis Currie, 1927 from Lesmahagow, and arachnidphylogeny. The Journalof Arachnology,27:86-93. Scotland, was originally thought to be Late Llandovery in age EICHWALD,E. 1854. Die Grauwackenschichtenvon Liv-und Esthland. and the earliest-known unequivocal synziphosurine but is now Bulletin de la Socidt6Imperiale des Nauralistesde Moscou, 27:1-211. believed to be Early Wenlock (Anderson, 1998). Bembicosoma ELDREDGE,N. 1974. Revision of the suborderSynziphosurina (Chelicer- pomphicus Laurie, 1899, a synziphosurine from the Late Llan- ata: Merostomata),with remarkson merostomephylogeny. American North Esk Inlier in the Pentland Hills of Scotland, of MuseumNovitates, Number 2543, 41 p. dovery horizon of the El Paso similar to the Waukesha has been rede- FLOWER,R. 1969. Merostomesfrom a Cotter age Lagerstitte, recently New Mexico Bureauof Mines and MineralResources Memoir, scribed by Anderson and Moore (2004) in terms of reference to Group. this with V. waukeshaensis it the ear- 22(4):35-44. group. Together represents HEYMONS,R. 1901. Die Entwicklungsgeschichteder Scolopender.Zool- As the earliest liest-known record of synziphosurines. one of syn- ogica, 33:1-244. ziphosurines, V. waukeshaensis bears a remarkable similarity to KLUESSENDORF,J. 1994. Predictabilityof SilurianFossil-Lagersthtten in Devonian taxa such as W. opitzi and L. lombardii, extending such North America.Lethaia, 27:337-344. a derived morphology back to the Llandovery. KLUESSENDORF,J., AND D. G. MIKULIC.1996. An early Silurian se- quence boundaryin Illinois and Wisconsin. Geological Society of ACKNOWLEDGMENTS AmericanSpecial Paper,306:177-185. KLUESSENDORF,J., ANDD. G. MIKULIC.1998. Paleokarst, sea-level fluc- We thank K. Westphal at the Geology Museum, University of tuationsand sequencestratigraphy in Silurianstrata of Illinois,Indiana, Wisconsin, Madison, for loan of material collected by G. Gun- andWisconsin. Geological Society of AmericaAbstracts with Program, derson and R. Meyer. S. Powell, University of Bristol, prepared 30(5):28. the photographs. E. Tetlie and S. Harris provided valuable com- LATREILLE,P. A. 1802. HistoireNaturelle, Gdndrale et Particulibre,des 3. 467 ments on the manuscript. P. Selden and J. Dunlop are thanked for Crustacdset des Insectes.Vol. E Dufart,Paris, p. and to the Part LAURIE,M. 1899. On a Silurianscorpion and some additionaleurypterid reviewing suggesting improvements manuscript. Hills. Transactionsof the of of this work was funded National Science Foundation remainsfrom the Pentland Royal Society by grant Earth 39:575-589. DEB 92-01048 to DGM and JK. RAM was funded NERC Edinburgh, Sciences, by LEHMANN,W. M. 1956. 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