THE EARLIEST SHREW (SORICIDAE, MAMMALIA) FROM THE MIDDLE EOCENE OF MONGOLIA

Abstract

The earliest and most primitive shrew, Soricolestes soricavus gen. et sp. nov. from the Middle Eocene Khaychin Formation of the Khaychin-Ula II locality, Mongolia, is described. Soricolestes has typical soricid lower molars and is characterized by well-differentiated antemolars, a large and semimolariform P4, the presence of the hypoconulid on M3, a long and low mandible, a deep masseteric fossa, and a superficial internal temporal fossa. The structural features of the lower jaw, antemolars, P4, and M 3 show that S. soricavus should be ranked as a separate subfamily, Soricolestinae subfam. nov.