A PLIOCENE (BLANCAN NALMA) OCCURRENCE OF THE URSAVINE BEAR, AGRIOTHERIUM CF. SCHNEIDERI FROM HAGERMAN FOSSIL BEDS NATIONAL MONUMENT, ID

Recently a partial dentary of the large ursavine bear, Agriotherium cf. schneideri, has been recovered from a mid Blancan NALMA locality at Hagerman Fossil Beds National Monument, Idaho. Agriotherium has been known previously only from mid - late Hemphillian aged sites in North America and has been considered a biostratigraphic indicator of Hemphillian NALMA deposits. Found in the Glenns Ferry Formation, the age of this specimen can be inferred from its stratigraphic position relative to radiometrically dated ash layers as between 3.79 Ma and 4.0 Ma. This age is supported by the presence of several other species at the same locality whose biostratigraphic ranges are confined to the Blancan; these include Pliopotamys minor, Cosomys primus, Ophiomys taylori, and Paracryptotis gidleyi.

This occurrence of Agriotherium from the mid-Blancan suggests that the species should not be used as a biostratigraphic indicator for the Hemphillian NALMA. The extinction of Agriotherium in North America has been attributed to its replacement by Ursus in the earliest Blancan. However, due to their ecological differences and the fact both ursids are represented in the Hagerman Local Fauna suggests replacement is unlikely. Currently, the Hagerman Agriotherium is the northernmost specimen of this bear found in North American suggesting a shift to more northern latitudes at the onset of the Pliocene Epoch.