A RARE AND DIVERSE LATE MIOCENE (HEMPHILLIAN) CARNIVORE FAUNA FROM NORTH-CENTRAL NEBRASKA, USA

Only two of several hundred vertebrate paleontology sites in the central Niobrara River valley of Nebraska contain mammalian fossils characteristic of the Hemphillian North American Land Mammal Age (NALMA). The Wyman Creek local fauna (or Rick Irwin site) was discovered during highway construction and contains several thousand identifiable specimens of Hemphillian age. These fragmentary remains were collected from an unconsolidated channel fill in the upper portions of the Ash Hollow Formation of the Ogallala Group. Reworked volcanic ash clasts in these fluvial sands are chemically matched with the Blacktail Creek tuff (6.62 Ma), thereby providing a maximum geochronologic age for the deposit. Mammalian taxa further constrain the age of the fauna to the late Hemphillian (Hh3).

Carnivoran remains representing seventeen species are nearly one-fifth of the identifiable specimens of large mammals. Canids include the widespread late Hemphillian taxa Eucyon davisi, Vulpes stenognathus, and Borophagus, as well as a rare occurrence of the hypocarnivorous borophagine Carpocyon limosus. Felids are represented by Machairodus cf. M. coloradensis and an indeterminate lynx-sized cat. The presence of the procyonid Bassariscus cf. B. ogallalae in the fauna documents a rare Great Plains occurrence. Nine genera of mustelids from the site include the badger Pliotaxidea nevadensis, wolverine Plesiogulo, and three mephitines (Martinogale alveodens, Pliogale furlongi, and Buisnictis cf. B. schoffi). A lower carnassial of the Eurasian badger Arctomeles records its first occurrence on the Great Plains. The Wyman Creek local fauna includes one of the most diverse Hemphillian carnivore assemblages yet described from North America.