Trilobites of the Late Cambrian Pterocephaliid biomere in the Great Basin, United States

The Pterocephaliid biomere is a biostratigraphic unit of stage magnitude that includes the most consistently fossiliferous parts of the Upper Cambrian in the Great Basin of western conterminous United States. The thickness of strata containing faunas of this biomere generally exceeds 500 feet. This interval includes units consisting of fine-grained detrital material and of clean carbonate rocks; the carbonate rocks probably represent sediments that composed a broad carbonate bank, and the units of detrital material represent belts of predominantly land-derived detrital sediments that flanked the bank on the east and west. The ptychoparioid trilobite fauna of the Pterocephaliid biomere consists of 112 species representing 51 genera. The sequence of faunas within the Pterocephaliid biomere is divided into five zonal assemblages that can be traced throughout the Great Basin. The assemblages are, in ascending order, the A.phelaspis zone, D·icanthopyge zone, Prehousia zone, Dunderbergia zone, and Elvinia zone. The first three zones, which are valid throughout the Great Basin, may correlate with beds currently assigned only to the Aphelaspis zone in central Texas and the southern Appalachian region. The principal faunal elements of the Pterocephaliid biomere probably invaded the Great Basin region from oceanic regions to the west and annihilated nearly all previously existing faunas of the older Crepicephalid biomere. The invading faunas then evolved in place and were in turn annihilated by a new invading fauna, which terminated the Pterocephaliid biomere. Several possible evolutionary series are described, including one that extends through five species and two genera. Geographic distribution of contemporaneous ornamented species in several genera suggests some correlation between environment and ornamentation in some groups of trilobites. New taxa are Oligometopus contractus n. sp. , Oheilocephalus brachyops n. sp. , Oheilocephalus granulosus n. sp. , Pseudokingstonia exotica n. gen., n. sp. , Iddingsia intermedia n. sp. , Apachia prima n. sp. , Dellea? punctata n. sp. , Dunderbergia calculosa n. sp. , Dunderbergia brevispina n. sp. , Elburgia intermedia n. sp. , Irvingella transversa n. sp. , H ardyoides mimicus n. sp. , Aciculolenus peculiaris n. gen., n. sp. , Xenocheilos granulosus n. sp. , Terranovella brevis n. sp. , Simulolenus quadrisulcatus n. gen., n. sp. , Dicanthopyge convergens n. gen., n. sp. , Dicanthopyge quadrata n. sp. , Dicanthopyge reductus n. sp. Aphelaspis longispina n. sp. Olenaspella paucisegmenta n. sp. , Litocephalus magnus n. sp. , Stenambon megagranulus _n. gen., n. sp. Stenambon paucigranulus n. sp. , Parahousia . ~Jllbequalis n. sp. , Prehousia diverta n. sp. , Prehousia impolita n. sp. , Preltousia indenta n. sp. , Prehousia pr·ima n. sp. , Tumicephalus depressus n. gen., n. sp. , Oernuolimbus laevifrons n. sp. , Oernuolimbus granulosus n. sp. , Strigambitus bilobus n. gen., n. sp. , Str-igambitus transversus n. sp. , Strigambitus? blepharina n. sp. , Pterocephalia? punctata n. sp. , Erimanium? brachyamis n. sp. , Erimanium multisegmentus n. sp. , Bromella veritas n. gen., n. sp. , Dytremacephalus asperamis n. sp. , Minupeltis definita n. sp. , Aphelotomon limbata n. gen., n. sp. , Aphelotomon punctata n. sp. , Aphelotomon spinosus n. sp. , Aphelotomon tnargi'iwta n. sp. , Aphelotomon granulosus n. sp. , Oomanchia minus n. sp. , Anechocephalus spinosus n. sp. , Morosa 'brevispina n. sp. , and Morosa emtensa n. sp.