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.