New genus of rodent from the Sespe Eocene

The structural characters and phylogenetic relationships of Tertiary aplodont rodents have been discussed by several authors. Although the earliest known aplodonts occur in the John Day formation, it has been advocated, especially by Matthew, that the origin of the group is to be found in the family Ischyromyidae as represented by the genera Prosciurus and Paramys. Schlosser, however, has suggested the derivation of the John Day genus from Sciurodon of the European Phosphorites.