Plionarctos is the oldest known genus in Ursidae's subfamily Tremarctinae which contains short faced bears. It is believed to be ancestral to both the Arctodus and Tremarctos genus. Plionarctos evolved from the genus Ursavus (possibly Ursavus brevirhinus) and existed from 10.3 million to 3.3 million years ago, from the Mid-Miocene to the early Pliocene Epoch. The three known sub-species of Plionarctos are Plionarctos edensis, Plionarctos harroldorum, and Plionarctos telonensis. Plionarctos was assigned to the bear family Ursidae in 1926 by paleontologist Childs Frick and to the subfamily Tremarctinae by R. M. Hunt in 1998.  The map below shows where Plionarctos fossils have been discovered.