The earliest known North American bovid, Neotragocerus

Abstract

ABSTRACT Neotragocerus represents the earliest recognized occurrence of the Bovidae in North America but is rare and poorly understood, known principally by scattered horn cores assigned to two species. Recently, the largest sample of Neotragocerus was discovered in the Fort Rock Formation of south-central Oregon where Eurasian immigrants co-occur. Horn cores, cranial fragments, dental material, and postcranial elements were found at five closely related sites and provide significant morphological data of this enigmatic ungulate. The specimens occurred in a ferruginous-stained basalt gravel that represents a paleochannel. Associated faunal elements indicate deposition during the Hemphillian NALMA, and 40Ar/39Ar dates from interbedded tephras, ranging from 6.11 + 0.08 to 5.74 + 0.01 Ma correspond with the Hemphillian assignment. Neotragocerus was a medium-sized bovid with relatively short horn cores, normally with dorsoventral ridges, ovate cross-section at the base, very short pedicles and a brachyselenodont dentition. Morphologies suggest assignment of Neotragocerus to the “Boselaphini,” the least derived tribe of living bovids or at least derivation from a “boselaphine” synapomorphic complex. The Hemphillian genus does not appear to be closely related to later occurring North American bovids, and a close Eurasian relative is not obvious. Based on the range of variation displayed by the Oregon specimens, Neotragocerus improvisus is retained, and Neotragocerus lindgreni is considered a nomen dubium.