Revised age of early short-faced bears (Tremarctinae, Plionarctos) in the fossil record

A carnivoran partial dentary with m2 from the late Miocene Rattlesnake Formation of Oregon was originally published as either an amphicyonid or ursid, and more recently as the tremarctine bear, Plionarctos. This identification represents the oldest purported record for short-faced bears, setting their biochronologic appearance at ~7 million years ago. Our re-assessment of this specimen indicates the m2 is morphologically consistent with Ursidae, but the fossil material cannot be confirmed as Plionarctos or even Tremarctinae. Based on this, the oldest unambiguous tremarctine is currently from the Eden Formation of California, and dates to ~5.6 Ma (late Miocene).