Review of the Rodentia of the Miocene period of North America ...

Abstract

Members of this order were very abundant during the White River and Truckee epochs in North America. They are referable to thirty- one species and eight genera. Of these genera three still exist in the regions where their fossil remains are found. These are Sciurus , Hesperomys, and Lepus. All of them occur in the Truckee beds, while the first-named only has been found in the White River formation. All of the species belong to the three great divisions of the order which now inhabit North America, while the fourth, the Hystricomorpha , which is very sparingly represented on the continent, has not yet been detected in the formations in question. It appears in a single species of porcu- pine in the Loup Fork beds.