ANALYSIS OF THE GEOLOGY, FAUNA, AND TAPHONOMY OF MORAVA-RANCH QUARRY,EARLY MIOCENE OF NORTHWEST NEBRASKA

The latest Arikareean (early Miocene) mammal fauna from Morava Ranch Q uarry, northwest Nebraska, U.S.A., is dominated by large perissodactyl s, including equids, rhinocerotids, and especially the chalicothere Mo ropus elatus. Lithic and faunal comparisons with the Agate Spring Quar ries and Harper Quarry, also from northwest Nebraska, suggest a simila r age and depositional environment, probably a transient waterhole in proximity to a fluvial system. Specimens are disarticulated and, in ma ny cases, broken in a pattern indicative of trampling. Weathering, abr asion, and Voorhies Group data suggest that the fauna is primarily aut ochthonous, with a small allochthonous component, primarily the oreodo nt artiodactyl Phenacocoelus. Loss of some easily transported elements suggests that the assemblage was winnowed slightly by water transport . Age profiles based on tooth wear suggest a death assemblage dominate d by mature, but not aged adults and reflect a mortality pattern inter mediate between attritional and catastrophic. A possible scenario for the formation of Morava Ranch Quarry involves drought, during which vu lnerable animals expired near waterholes, underwent disarticulation an d trampling, and were buried by sediment brought in by wind and period ic flooding.