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A Silurian Soft-Bodied Biota Author(S): Donald G A Silurian Soft-Bodied Biota Author(s): Donald G. Mikulic, Derek E. G. Briggs, Joanne Kluessendorf Source: Science, New Series, Vol. 228, No. 4700 (May 10, 1985), pp. 715-717 Published by: American Association for the Advancement of Science Stable URL: http://www.jstor.org/stable/1694543 Accessed: 24/02/2010 21:52 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=aaas. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve and extend access to Science. http://www.jstor.org cept where infilled by diagenetic fluor- apatite. Cuticle sculpture is unusually well preserved in most specimens of worms and phyllocarids; hexagonal lenses of compoundeyes are occasional- ly evident. Predominantlyarticulated tri- lobites and the absence of any fossil Reports alignment or variation in orientation in bedding suggest gentle transport. Crustaceansinclude phyllocarids and a leperditicopidostracode. The earliest example of the OrderConcavicarida, an A Silurian Soft-Bodied Biota enigmaticgroup that may comprise crus- taceans, is also present. The separate Abstract. A new Silurian (Llandoverian) biota from Wisconsin with a significant status of these arthropods was recog- soft-bodied and lightly sclerotized component is dominated by arthropods and nized only recently; the previously old- worms. The fauna includes the earliest well-preserved xiphosure, a possible marine est known example is from the early uniramian, three new arthropods of uncertain affinity, and possibly the first Devonian (Emsian) of Czechoslovakia Paleozoic leech. This may be only the second locality to yield a conodont animal. (7). Our materialshows at least three of Lack of a normal shelly fauna suggests an unusual environment. The discovery adds the raptorialappendages, which are oth- significantly to the few such exceptionally preserved faunas known from Lower erwise known only from genera in the Paleozoic rocks. Jurassic of Italy and France (8). This Silurianoccurrence extends the tempo- Occurrencesof soft-bodied organisms The most numerousand diverse are trilo- ral rangeof the groupby about 40 million are of great importancein a fossil record bites, which lack soft parts; a dalmanitid years. overwhelmingly dominated by mineral- dominatesthe 13 genera. All three other The fauna includes what may be the ized skeletal remains. Such Konservat major arthropod groups-crustaceans, earliest completely preserved xiphos- Lagerstitten (1) are'the only evidence chelicerates, and uniramians-are repre- uran chelicerate (Fig. 2A), which is only suggesting the true biotic diversity of sented by lightly sclerotized forms. New the second known Paleozoic example ancientenvironments, the historyof taxa arthropods, which can be assigned to showing evidence of limb morphology with low fossilization potentials, and the these groups only tentatively, if at all, (9). The semicircularprosoma has pro- nature of soft and lightly sclerotized tis- are also present. There are at least four nounced radiating ridges in the inter- sue of shelly forms. Few Lagerstaitten worm taxa. Ostracodes, graptolites,and ophthalmic area. One specimen shows are known from the 100-million-yearin- conulariids are common in places. Al- traces of six pairs of prosomallimbs; the terval between the famous Middle Cam- gae, ?hydroids, monaxonid sponges, tip of the sixth appears to bear a chela, brian Burgess shale of British Columbia nautiloids,and brachiopodsare rare. Mi- the first known documentation of this (2) and the Lower Devonian Hunsriick- crofauna includes conodont elements feature in the group. This arthropod schiefer of West Germany (3). A new (including coniform fused clusters) (6) bears some similarity to the poorly biota from the lower Silurianof Wauke- and foraminiferans. known Bunaia woodwardifrom the Silu- sha County, near Milwaukee,helps to fill The shelly fossils are decalcified and rian Bertie Waterlimeof New York, but this interval. slightly compacted. The soft-bodied and appearsto be a new Synziphosurine(10). The Waukesha biota comes from a lightly sclerotized taxa are flattened ex- With the possible exception of Ay- unique depositional environmentrepre- sheaia from the Middle Cambrian(11), sented by basal Brandon Bridge strata the oldest uniramiansare latest Silurian (4) in finely laminatedargillaceous dolo- myriapodsof the Scottish Old Red Sand- mite found at only one locality. These stone (12). Although myriapods are ter- rocks are dated as latest Llandoverianon restrial, it is widely assumed that they the basis of the graptoliteMonograptus originated in water. Thus a myriapod- spiralis; late Llandoverianto early Wen- like animal (Fig. 2B) in our material is lockian conodonts occur in the upper- particularlyinteresting. The animalhas a most Brandon Bridge (5). The occur- distinct head bearing ?eyes and at least rence of the trilobite Stenopareia indi- three limbs, a trunk of about 11 limb- cates that the Brandon Bridge is no bearing divisions, and a terminaltelson younger than early Wenlockian. with a posteriorly projecting ventral Strata containing soft-bodied fossils process. Each trunk division appears to are found only where the Brandon consist of two sections, the longer ap- Bridge wedges out against an 8-m-high pendage-bearing,the shorter not; they scarp of cherty dolomite (Fig. 1). North resemble diplosegments although each of this Brandon is scarp Bridge absent; 1. relation bears only one pair of limbs. The limbs to the the Fig. Diagramshowing stratigraphic south cherty dolomite is ab- between the lower Silurian Brandon Bridge are jointed, have an expanded base, and sent. Thus distributionof the Waukesha and adjacent Silurian units. (A) Kankakee taper distally; there is no evidence that biota appearsto be strictly controlledby Formation;(B) unnamedcherty dolomite;(C) they are biramous.This animalmay rep- depositionaland process- Brandon Bridge strata; and (D) Waukesha resent a new class of marineuniramians. preservational Dolomite. Soft-bodied biota occurs es related to the environment of the only The affinitiesof the other new arthro- where BrandonBridge (C) wedges out against scarp. cherty dolomite (B). Vertical scale approxi- pods in the fauna are more problematic. The fauna is dominatedby arthropods. mately, 15 m; horizontalscale, 100 m. The most common lightly sclerotized 10MAY 1985 715 taxon (Fig. 2C) is elongate and worm- mistakenfor anostracans, but any simi- Protoscolex and Palaeoscolex. These like, with an anteriorhead shield and 30 larity to a nymph is superficial in this annulate worms, ranging from Lower to 40 trunk tergites. A large compound case (14). The Remipediahave no prov- Cambrianto upper Silurian,form a dis- eye and at least one antenna-likeappen- en fossil record; the possibility of a rela- tinct group that may be a separate class dage project anteriorlybeyond the head tion with the problematicPennsylvanian of annelids (16). shield. The head also bears two pairs of arthropod Tesnusocaris is equivocal A larger,rare annulateworm (Fig. 2F) long segmented limbs. The poorly (15). The affinitiesof this Waukeshaar- appears to lack papillae, although the known trunk limbs are short lobe-like thropodare uncertain. cuticle is not preserved. The best speci- structures. This arthropod bears some The most problematicmember of the men terminatesin a circularstructure at resemblanceto the Kazacharthra,an ex- fauna is poorly preserved (Fig. 2E). the only end preserved. Setae or other tinct order of branchiopod crustaceans Large, laterally extending, slightly con- lateral projections are not evident. The known only from the Jurassic (13). vex structuresmay representa bivalved circle resembles the suckers of leeches The best preserved arthropod (Fig. carapace.Small specimens (10 to 20 mm but in the absence of more diagnostic 2D) has largecompound eyes overlyinga long) show an axial line, possibly a characters any assignment is tentative. massive head appendage, which may hinge, and a pronouncedposterior inden- Fossil Hirudinea are otherwise known have been adapted to seize prey. Other tationbeyond which extends a trunk-like only from the Upper Jurassic of West head appendages may have existed but structureof seven to eight divisions. The Germany (17). The large size of this are not clearly preserved. The trunkhas presumedhead region, bearingtwo large worm relative to the rest of the fauna about 11 somites in most specimens, lateral circular structures that may be suggests that, if it were a leech, it was
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