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Lower Resolution THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS December 16, 1981 Paper 106 LARGER BIVALVE ARTHROPODS FROM THE MIDDLE CAMBRIAN OF UTAH' R. A. ROBISON and Ft—. C. RICHARDS Department of Geology. University of Kansas, Lawrence, Kansas 66045, and Geological Survey of Canada, Calgary, Canada T2L 2A7 Abstract—Carapaces or valves of 12 species of larger bivalve arthropods and one spe- cies of an associated univalve arthropod are described from Middle Cambrian strata of northern and western Utah. Some of these bivalve species represent phyllocarid Malacostraca whereas others may represent either phyllocarids or Branchiopoda. Af- finity of the univalve species is less certain. One genus and five species of larger bi- valves are new, the new genus being Dicerocaris and the new species being Dicerocaris opisthoeces, Perspicaris? dziatus, Perspicaris? ellipsopelta, Tuzoia guntheri, and Tuzoia? pet erseni. Specimens of Branchiocaris? sp., Canadaspis cf. C. perfecta (Walcott), Dioxycaris argenta (Walcott), Proboscicaris agnosta Rolfe, Pseudoarc- tole pis sharpi Brooks and Caster, Tuzoia retifera Walcott, and an undetermined genus and species are illustrated and discussed. Three distinctive univalve carapaces are assigned to the new genus and new species Pahvantia hastata. Collectively, the specimens provide important information concerning the distribution and species diversity of a poorly known element of the Cambrian fauna. EXTENSIVE SEARCHES and generous contribu- larger collection of such Cambrian fossils is tions by several persons during the past two that from the famous Burgess Shale in British decades have made possible the assembly of a Columbia. This paper includes descriptions of collection of more than 100 carapaces or disar- 12 larger bivalve arthropod species and one ticulated valves of larger bivalve arthropods probable univalve species. from Middle Cambrian strata in Utah (Fig. 1). Larger bivalve arthropods have been re- Because in life the exoskeletons of these ar- ported from few Cambrian formations in thropods were not mineralized, their preserva- North America. Several species, some of which tion is uncommon. To our knowledge, the only we consider to be synonyms, have been de- scribed from the Burgess Shale of Middle Cam- 'Manuscript received August 21, 1981 , brian age (Walcott, 1912a; Resser, 1929; 2 The University of Kansas Paleontological Contributions Paper 106 Rolfe, 1962; Simonetta and Delle Cave, 1975; bivalve carapaces. With only the carapace it Briggs, 1976, 1977, 1978). Distribution else- may be difficult, if not impossible, to distin- where in western North America, includes guish representatives of families of phyllocarid three species from the Eager Formation of Malacostraca from those of the Protocarididae, Early Cambrian age in British Columbia which show closest affinities with the Branchio- (Resser, 1929); one species from the Ophir poda (Briggs, 1976, p. 12). Because soft parts Shale (Walcott, 1886) and another from the and appendages are not preserved with cara- Wheeler Formation (Brooks and Caster, 1956), paces of any known bivalve arthropod from the both of Middle Cambrian age in Utah. In east- Cambrian of Utah, generic identifications for ern North America, six species have been de- some specimens are questionable. Also, the scribed from the Kinzers Formation in Pennsyl- family, order, and even class assignments are vania (Resser, 1929; Resser and Howell, 1938) uncertain for most. Nevertheless, we believe and two species from the Parker Shale in Ver- that these specimens warrant description mont (Resser and Howell, 1938), all of Early because they provide important information Cambrian age; one species from the Rogersville about the distribution and species diversity of a Shale of Middle Cambrian age in Tennessee poorly known element of the Cambrian fauna. (Resser, 1938); and two species from the Trilobites are the most abundant inverte- Nolichucky Formation of Late Cambrian age brate fossils in most Cambrian strata, partly at in Alabama (Resser, 1938). least because many trilobites possessed a well- calcified dorsal exoskeleton with a high poten- tial for preservation. Evidence from the excep- tionally preserved fauna of the Burgess Shale Wellsville • Bear River Range indicates that species of nontrilobite arthro- Mountains pods actually outnumber those of trilobites by more than two to one, and individuals of some species are far more common than those of tri- Salt Lake City f# lobites (Conway Morris, 1979; Conway Morris • Wasatch Range and Whittington, 1979; Whittington, 1980). Moreover, preliminary comparison of total numbers and proportions of normally pre- served genera from different formations sug- • Drum Mountains gests that composition of the biota of the • House Range Burgess Shale, rather than being unusual, is probably representative of Middle Cambrian, low-latitude, open-shelf environments in North America (Conway Morris and Robison, 1982). UTAH The assemblages of rarely preserved, larger bivalve arthropods in the Middle Cambrian of Utah also bear strong resemblances to the assemblage in the Burgess Shale. This further supports the notion of normality for the Burgess biota. 0 km 100 Stratigraphy. — In general, lithostrati- graphic nomenclature in this paper conforms to the usage of Oriel and Armstrong (1971) for Fig. 1. Areas in Utah from which larger bivalve arthropods Utah and of Middle Cambrian age have been collected. northern Hintze and Robison (1975) for west-central Utah. The total observed stratigraphic ranges for From studies of Burgess Shale specimens all species of larger bivalve arthropods pres- that are preserved with soft parts and append- ently known from Cambrian strata in Utah are ages, Briggs (1976, 1977, 1978) has demon- plotted on Figure 2. Relevant biofacies rela- strated that morphologically very different tionships and biostratigraphic nomenclature arthropod bodies may possess quite similar have been discussed by Robison (1976, 1982). Robison Ce Richards Larger Bivalve Arthropods from the Middle Cambrian 3 tunate to find one such arthropod for every sev- Agnostoid eral thousand trilobites. Several other localities Interval- Species Ranges have yielded only one or a few specimens of a Zones single species. These less productive localities \ are described under the "Occurrence" of rele- Lc jopyge vant species in the Systematic Descriptions. All amnia localities are within the mountains or ranges Lejopyge plotted on Figure 1. calva 114. Medium-dark-gray, laminated, calcare- ous mudstone in the uppermost 3 m of ii the Wheeler Formation on a north-trend- Ptychagnostus ;' ing ridge crest; sec. 24 (unsurveyed), T. punctuosus F.) ,': 1 _.'''1 . 21 .....: . ., t; 16S., R. 13W.; about 700 m south of a ,3 a. Q. ù ; ii t.., r: 2 .:.2 4::.: .2 stock-watering trough that is supplied by .g.,f,, --ti .L, ii water piped from Swasey Spring on the 0 east side of the House Range. t f,..t , t., z e . 4 ... .4 4°., 4' 4 i-. Gc'h E- -F-I 115. Medium- to dark-gray, calcareous mud- -5 1 Z Pt ychagnostu s stone in the uppermost 30 m of the E i < a tavus II II II II II II li Wheeler Formation at its type locality in E R .. Wheeler Amphitheater; SE1/4 sec. 2, T. co t-. .tt 17 S., R. 13W.; central House Range. < Ptych. gibbus L.) 716. A 60-m unit of yellowish-gray to grayish. a.F, w orange calcareous mudstone in the upper _J I," 0 12 Marjum Formation; exposed in ledges t _0 Ptycliagnostus ••• .t-' along the south side of a large dry wash in praecurrens the SW 1/4NW 1/4 sec. 24 (unsurveyed), T. 17 S., R. 13W.; about 4 km due south of Wheeler Amphitheater in the central House Range. The stratigraphic position i n of this mudstone unit has not been pre- (..) cisely determined; however, its basal beds Perono psis . are probably about 300 m above the base bonnerensis of the Marjum Formation. 745. Brown-weathering, dark-gray, lami- nated, lime mudstone about 180 to 200 m above the base of the Marjum Forma- tion; SW 1/4SE1/4 sec. 13 (unsurveyed), T. 18 S., R. 13 W.; east side of Bird Can- unnamed yon, House Range. Repositories. — Most of the specimens de- scribed or illustrated in this paper are in the Fig. 2. Observed stratigraphic ranges of larger bivalve ar- Invertebrate Paleontology, Univer- thropods from the Middle Cambrian of Utah. Also in- Museum of cluded is the probable arthropod Pahvantia hastata, new sity of Kansas (KUMIP). A few specimens, in- genus and new species. cluding the holotype of Dioxycaris argenta (Walcott), are in collections of the U.S. Na- tional Museum of Natural History (USNM), Localities. - The majority of specimens de- Washington, D.C. A few unillustrated speci- scribed here are from four localities. These are mens are in the collections of Brigham Young listed below and are referred to by number in University, Provo, Utah, and others are in the the section on Systematic Descriptions. Nontri private collection of Lloyd Gunther, Brigham lobite arthropods are not common at any of City, Utah. these localities. Usually a collector will be for- A cknowledgments. —Without the generous 4 The University of Kansas Paleontological Contributions—Paper 106 contributions and support of several persons, of the University of Kansas. Michael Frederick this study would be far less complete. Excep- aided with photography, R. B. Williams pre- tional contributions were made by Lloyd, pared the figures, and Virginia Ashlock, D. E. Metta, and Val Gunther of Brigham City, G. Briggs, K. E. Caster, and A. J. Rowell criti- Utah, and R. L. Harris of Delta, Utah. Other cally reviewed an early draft of the manuscript. important contributions of material were made This study was supported by National Science by L. F. Hintze and M. S. Petersen of Brigham Foundation grant EAR-7708689 and the Wal- Young University; R. F. Kohl of Willows, Cali- lace E. Pratt Research Fund, which is provided fornia; W. L. Stokes of the University of Utah; to the University of Kansas by the Exxon USA and D. C. Kopaska-Merkel and G.
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