LATE GRIESBACHIAN (EARLY TRIASSIC) AMMONOIDS AND NAUTILOIDS FROM THE DINWOODY FORMATION AT CRITTENDEN SPRINGS, ELKO COUNTY, NEVADA
by
JAMES F. JENKS, TAKUMI MAEKAWA, DAVID WARE, YASUNARI SHIGETA, ARNAUD BRAYARD and KEVIN G. BYLUND
Abstract—We document a relatively small but very important late Griesbachian ammonoid and nautiloid assemblage from the Dinwoody Formation at Crittenden Springs, Elko County, Nevada. This discovery represents the first significant report of late Griesbachian ammonoids in the low-paleolatitudes of eastern Panthalassa, and it also signifies the first report of Wordieoceras wordiei and two co-occurring taxa outside of the Boreal Realm. This similarity in ammonoid faunas, irrespective of paleolatitude, provides support for the concept of weak latitudinal diversity gradients following the end-Permian extinction. The finding is even more noteworthy given the Dinwoody Formation’s reputation for poor fossil preservation and a near complete absence of documented and identifiable ammonoid and nautiloid occurrences. Consisting of four taxa of which two are newly described, the ammonoid fauna includes Wordieoceras wordiei (Spath), Kyoktites cf. K. hebeiseni Ware and Bucher, Wordieoceras mullenae n. sp. and a new taxon belonging to the Mullericeratidae family, Ophimullericeras paullae n. gen., n. sp. The nautiloids are attributed to a newly described species, i.e., Xiaohenautilus mulleni n. sp., a genus heretofore unknown in eastern Panthalassa but commonly reported from the late Griesbachian of South Primorye and the late Griesbachian/early Dienerian of South China.
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