Mentoclaenodon is an extinct genus of arctocyonid ungulate mammals.

Mentoclaenodon had large upper canines comparable to the "saber-teeth" of various Miocene and Pleistocene feliform saber-toothed cats.

This genus and its sister-genus Anacodon, and the oxyaenid Machaeroides were the first true mammals to develop saber-teeth.

(The various saber-tooth gorgonopsian genera, such as Inostrancevia and Ruhuhucerberus, are regarded as "stem-mammals" that are close relatives of true mammals).

It is also thought to be one of the earliest known Cenozoic-aged mammalian predators that would have preyed on other mammals.