Giant short-faced bears (Arctodus simus) in Pleistocene Florida USA, a substantial range extension

Fossils of the giant short-faced bear, Arctodus simus (Cope, 1879), have been recovered from over 100 localities in North America, extending from Mexico to Alaska and California to Virginia. Despite this large range, the species has never been recorded from the southeastern United States. The lesser short-faced bear, Arctodus pristinus Leidy, 1854 is well represented from this region, particularly Florida, but all known occurrences are late Pliocene-middle Pleistocene in age (about 2.5 to 0.3 Ma). Differentiating A. simus from A. pristinus can be difficult because large individuals of A. pristinus overlap in size with small individuals of A. simus, and there are few morphological differences. However, these two taxa can be clearly separated based on the relative proportions of their molars and premolars. Two Pleistocene records of A. simus representing a minimum of three individuals from the Withlacoochee River drainage of central Florida are reported here, substantially extending the distribution of this massive bear into southeastern North America. A late Pleistocene age for these occurrences is corroborated by an associated Rancholabrean fauna and rare earth elemental analyses. One of the reported individuals is quite large, supporting the hypothesis of extreme sexual dimorphism in A. simus and rejecting a hypothesis of two subspecies.