A NEW SPECIES OF MIMOTONID FROM THE MIDDLE EOCENE OF MONGOLIA: EVIDENCE FOR THE EVOLUTION OF LAGOMORPHA

A new species of mimotonid from Tsagan Khutel locality, Valley of Lakes, Mongolia is described. Mimotonids have recently been recognized as the likely ancestors to Lagomorpha (rabbits, hares, and pikas), although several important features distinguish them from modern and fossil lagomorphs. This new material helps bridge the gap between mimotonids and lagomorphs as the specimen described here shows typical mimotonid features while also exhibiting several derived lagomorph features. The material consists of a right dentary, including cheek teeth and one of two lower incisors that were present. The dental features of this species are similar to the mimotonid G. elkema, but several derived features distinguish this material from all other mimotonids and confirm its designation as a new species. The features include an overall elongation of the snout, more gracile dentary, and an enlargement of the p4. Geologic and paleontologic evidence suggests that the material is of Middle Eocene age, consistent with its transitional morphology, making this the youngest known occurrence of mimotonid.