The first Old World occurrence of the North American mustelid Sthenictis (Mammalia, Carnivora)

The Tunggur Formation in Inner Mongolia has produced a well-known middle Miocene Platybelodon fauna; this fauna has provided some evidence of intercontinental exchanges of carnivoran taxa during that time. Here we describe a new immigrant mustelid from the Tunggur Formation. The new material, composed of two partial dentaries, belongs to the genus Sthenictis. A new species, S. neimengguensis n. sp., is named after the dentaries which represent the first occurrence of this genus outside North America. Sthenictis neimengguensis n. sp. is closest in size and morphology to the North American S. dolichops, but the former has a more slender dentition and mandible. In terms of carnassial morphology, the less trenchant ml talonid and a well-developed ml metaconid in S. neimengguensis n. sp. are plesiomorphic characters of the Mustelinae. The relatively elongated tooth row and simple premolar morphology, however, unites it with other species of Sthenictis. This combination of characters excludes Sthenictis from both the highly hypercarnivorous Hoplictis-Ischyrictis-Eomellivora group and Iberictis-Plesiogulo group, and seems to represent that of a basal lineage with intermediate morphology.