THE MUSTELID STHENICTIS IN MONGOLIA: IMMIGRANT FROM NORTH AMERICA

A lower jaw of the mustelid Sthenictis was recently recovered from the middle Miocene Tunggur Formation, Inner Mongolia, China. In size and morphology, it is slightly larger than Sthenictis bellus from the late Hemingfordian Sheep Creek Fm. of Nebraska, and S. junturensis from the early Clarendonian Black Butte l.f. of the Juntura Fm., southeastern Oregon. It is slightly smaller and less robust than S. dolichops from the early Barstovian Olcott Fm., Nebraska, S. robustus from the late Barstovian (Valentine Fm.) of Nebraska, and S. lacota from the Clarendonian of South Dakota. It is most similar to an undescribed new specimen (F:AM 25235) of Sthenictis from the Burge fauna (late Barstovian) of Nebraska, which is probably a new species. Thus, the Mongolian specimen suggests that Sthenictis migrated from North America to Mongolia in the middle Miocene. This is yet another example of how mustelids, although rare, are valuable indicators of migrational trends between Eurasia and North America, and also good biochronological indicators.