THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS July 24, 1984 Paper 111 EXCEPTIONALLY PRESERVED NONTRILOBITE ARTHROPODS AND ANOMALOCARIS FROM THE MIDDLE CAMBRIAN OF UTAH' D. E. G. BRIGGS and R. A. ROBISON Department of Geology, Goldsmiths' College, University of London, Creek Road, London SE8 3BU, and Department of Geology, University of Kansas, Lawrence, Kansas 66045 Abstract—For the first time arthropods with preserved soft parts and appendages are recorded from Middle Cambrian strata in Utah. Occurrences of four nontrilobite taxa are described, including Branchiocaris pretiosa (Resser) and Emeraldella? sp. from the Marjum Formation, Sidneyia? sp. from the Wheeler Formation, and Leanchoilia? hanceyi, n. sp., from the Spence Shale. A small specimen of the giant predator Anomalocaris nathorsti (Walcott) also is described from the Marjum Formation. These occurrences extend upward the observed stratigraphie ranges of Anomalocaris, Branchiocaris, and questionably Emeraldella and Sidneyia. Emeraldella, Leanchoilia, and Sidneyia hitherto have been recorded from only the Stephen Formation in British Columbia. Further evaluation indicates that Dicerocaris opisthoeces Robison and Rich- ards, 1981, is a junior synonym of Pseudoarctolepis sharpi Brooks and Caster, 1956. DURING RECENT years, intensive collecting has 1983). Although providing little new morpho- produced rare but diverse, soft-bodied or scler- logic data, the Utah specimens are important otized Middle Cambrian fossils from several because of new information they provide about localities in Utah. Most of the taxa are the same the geographic and stratigraphie distribution of as or similar to those previously described from a rarely preserved part of the Middle Cambrian the famous Burgess shale of the Stephen For- biota. They support the notions that the Bur- mation in British Columbia (e.g., Whittington, gess shale biota is unusual only in its preserva- 1980; Collins, Briggs, and Conway Morris, tion (Conway Morris and Whittington, 1979) and probably is representative of upper open- I Manuscript received March 6, 1984. shelf Middle Cambrian environments of west- 2 The University of Kansas Paleontological Contributions—Paper 111 with preserved appendages and soft parts to be Wellsville Mountains reported from Utah. • Repositories. —Illustrated specimens are with collections of either the National Museum of Natural History (USNM) or the University of Salt Lake City OS Kansas Museum of Invertebrate Paleontology (KUMIP). Acknowledgments. —Several of the specimens were collected by Lloyd, Metta, and Val Gunther. Other single specimens were collected by Robert Drachuk, Robert Fife, Jeff Hancey, • House Range and Thomas T. Johnson. A preliminary draft of this paper was improved by helpful sug- gestions from Virginia Ashlock, Desmond Col- lins, Simon Conway Morris, M. N. Rees, A. J. UTAH Rowell, and H. B. Whittington. Illustrations were prepared by Roger B. Williams. Some of the Gunther's collecting expenses were sup- ported by National Science Foundation grant EAR-8201428 to Prof. J. Keith Rigby of Brig- km 100 ham Young University. D. E. G. Briggs' work was carried out while on sabbatical leave at the Field Museum of Natural History, Chicago, Visiting Scientist Fig. I. Areas in Utah (dots) where Middle Cambrian fossils under the auspices of the were collected. Program, with additional support from the Royal Society and Goldsmiths' College Re- search Fund. Some publication costs were sup- ern North America (Conway Morris and Robi- ported by NSF grant EAR-8024066 to R. A. son, 1982). The purpose of this paper is to Robison. We are grateful for all of this help. document new occurrences of Anomalocaris and four taxa of unmineralized arthropods from the GEOLOGIC SETTING House Range and Wellsville Mountains of Inferred temporal relationships of most Utah (Fig. 1). stratigraphic units cited in this paper are shown Few nontrilobite arthropods have previ- in Figure 2. Lithostratigraphic nomenclature ously been described from Cambrian strata of for the House Range conforms to usage by Utah. Most of these are valves of phyllocarids Hintze and Robison (1975). Lithostratigraphic or protocaridids from various Middle Cam- units in the Wellsville Mountains need further brian formations (Walcott, 1886; Brooks and study and possible revision of nomenclature. Caster, 1956; Briggs, 1976; Gtinther and Middle Cambrian lithofacies in western Gunther, 1981; Robison and Richards, 1981). North America indicate the presence of a broad A single specimen of the aglaspid Beckwithia typa continental shelf. Thick deposits of shallow- was described by Resser (1931). Single Molaria- water, platform sediment accumulated along and Mollisonia-like specimens from the Wheeler the inner shelf. Commonly, a carbonate shoal Formation and two merostomelike specimens complex along the seaward margin of the plat- from the Spence Shale were illustrated by form was flanked by a restricted inshore basin Gunther and Gunther (1981). Two specimens on one side and deeper open shelf on the other from the Wheeler Formation were described by side (Robison, 1976; Aitken, 1978). During Conway Morris and Robison (1982) as the much of the Middle Cambrian two almost medusoid Peytoia cf. P. nathorsti; however, those mutually exclusive biotopes were separated by now are known to be the jaws of Anomalocaris probable salinity and temperature barriers over nathorsti (Whittington and Briggs, 1982, in the carbonate shoals. An inner restricted-shelf press). Specimens described here are the first biofacies generally is characterized by sparse, Briggs & Robison—Cambrian Arthropods and Anomalocaris 3 CO TRILOBITE ZONES FORMATIONS Lu cc - shelf House Wellsville LLI restricted - shelf open - shelf open w polymeroids polymeroids agnostoids Range Mountains Lie commonly barren Cedaria 0 rt3 Weeks cr) — upper ›, co a C3) — _ ...... (I) CL) Eldoradia -J al lower Z Ptychagnostus Marjum Bloomington < Bolaspidella punctuosus ET co 2 commonly barren < Ptychagnostus U atavus Wheeler — — in Ptychagnostus gibbus o —o Ptychagnostus Ehmaniella praecurrens Oryctocephalus Perono psis Glosso pleura bonnerensis Spence Albertella Plagiura Fig. 2. Interred temporal relationships of some stratigraphic units in Utah (see Robison, 1976, I984a . The Burgess shale of the Stephen Formation in British Columbia contains a fauna representative or the Ptychagnostus praecurrem and upper 0;7/1w/thaw zones. Formation names not relevant to this paper are omitted. Dashed lines denote uncertain position of boundaries. Thicknesses of units are not shown to scale. low-diversity, polymeroid trilobites. An outer verse open-shelf trilobite fauna containing Bath- open-shelf biofacies is characterized by com- yuriscus and Elrathina above a restricted-shelf mon, high-diversity, polymeroid and agnostoid fauna dominated by Glossopleura. These faunas trilobites. Fossils are usually most abundant have traditionally been assigned to different near the seaward margin of the carbonate plat- zones (e.g., Howell and others, 1944; Loch- form facies. man-Balk and Wilson, 1958). Nevertheless, In places during the early Middle Cam- total stratigraphie ranges of both Bathyuriscus brian, carbonate shoals were poorly developed and Elrathina have been observed to overlap and disjunct. This allowed the intermingling of completely the range of Glossopleura (Robison, faunas that more commonly were confined to 1976). In the Spence Shale of the Wellsville either restricted- or open-shelf environments. Mountains species of Bathyuriscus, Elrathina, and An example of such intermingling is the fauna Glossopleura are associated in the same beds of the Spence Shale in the Wellsville Moun- (Campbell, 1974: fig. 4). These distribution tains. The Spence is characterized by abundant patterns are part of the basis for proposed fossils and high taxonomic diversity (e.g., Res- abandonment of Bathyuriscus-Elrathina as a zone ser, 1939; Campbell, 1974). It has yielded one name (Robison, 1976). The patterns also are of the fossils, Leanchoilia? hanceyi, n. sp., which important with regard to interpretations that is described here. have been made about the depositional setting A general marine transgression during the of the Burgess shale in British Columbia. Middle Cambrian widely superimposed a di- The Burgess shale has been determined to 4 The University of Kansas Paleontological Contributions—Paper 111 represent part of a sediment apron that accu- indicative of a low-energy, gently sloping ramp. mulated adjacent to a near-vertical submarine Coeval, intertidal, carbonate platform litho- escarpment (Fritz, 1971; McIlreath, 1975, facies are no more than a few kilometers away. 1977). Using the uppermost occurrences of Fossils here described from the Wheeler Forma- Glossopleura as a time surface, Fritz (1971:1161- tion are preserved in similar rocks; however, 1163, fig. 2) calculated that minimum water the platform margin was probably a few tens of depth at the front of the escarpment exceeded kilometers away and the water was probably 200 meters. Based on observed distribution deeper. Paleogeographic reconstruction (e.g., patterns of faunas containing Glossopleura and Bambach, Scotese, and Ziegler, 1980) indicates Bathyuriscus-Elrathina, we suggest that the a position in equatorial latitudes. boundary between these faunas may have Many Wheeler and Marjum beds are un- greater ecological than temporal significance fossiliferous. Others range from sparsely to and inferred water depths during Burgess shale abundantly fossiliferous.