THE EARLIEST ORDOVICIAN CEPHALOPODS OF EASTERN LAURENTIA— ELLESMEROCERIDS OF THE TRIBES HILL FORMATION, EASTERN NEW YORK

The Tribes Hill Formation (upper Skullrockian) of New York records the earliest Ordovician diversification of cephalopods, in particular ellesmerocerids, on the east Laurentian, shallow carbonate platform. Revision of this cephalopod fauna on the basis of approximately 430 specimens collected across eastern New York has led to new information on inter- and intraspecific variation of the taxa and extensive synonymization of species-level taxa. The Ellesmeroceratidae and Protocycloceratidae, Ellesmeroceras, and Eremoceras are emended, Eorudolfoceras n. gen. and Dakeoceras champlainense n. sp. are erected. A rank abundance plot of the 342 specimens at a locality in the Lake Champlain lowlands provides information on the community structure of the nautiloid fauna, where small orthoconic taxa are shown to dominate strongly. The small orthocone Ectenolites was the most common genus in terms of total occurrences, was the most paleogeographically widespread genus, and was the only genus to cross the Cambrian-Ordovician boundary.