PaleoBios

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 as Tremarctinae represents the oldest purported record for that group, 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).