THE EARLIEST HAPALODECTES (MESONYCHIA, MAMMALIA) FROM THE PALEOCENE OF MONGOLIA

Abstract

A lower jaw containing complete tooth rows of the earliest hapalodectid mesonychian, Hapalodectes dux sp. nov., is described from the Upper Paleocene of Tsagan-Khushu, Mongolia (Naran Bulak Formation, Zhigden Member). The new species is smaller than the Middle Eocene H. serus and larger than the Early Eocene H. hetangensis. The lower molars of H. dux have distinct metaconid, protocristid, rudimentary hypoconulid, and entoconid; M2 and M3 are equal in size. These characters suggest that H. dux is the most primitive species of the genus Hapalodectes.