A Galerella-like small mongoose from ca. 10 Ma of Kenya

抄録

Dentognathic fossil specimens of a Galerella-like small mongoose (Mammalia, Carnivora, Herpestidae) are described from the basal upper Miocene (ca. 10 Ma; Tortonian) Nakali Formation of central Kenya. They show comparable dental morphology to extant Herpestes, Xenogale, Galerella, and Urva: a better-developed parastylar shelf than the metastylar region on upper first molar (M1), an absence of the metastyle on M1, a trenchant and enlarged trigonid with a well-developed prevalid (mesial shearing blade) on lower first molar (m1), and much smaller m2 compared to m1. Compared with fossil “Herpestes”-like genera, the Nakali specimens are distinguished from them: they differ from Herpestides in being smaller and in having a much less developed cingulum on M1; from Leptoplesictis, Dunictis, and Forsythictis in having a less mesially-protruded paraconid (less mesiodistally-elongated prevalid) on m1; from Ugandictis and Kichechia in having a better-developed prevalid on m1, a much smaller m1 talonid, and much smaller m2 compared to m1. Taking the very small size into account, the Nakali specimens are more comparable to Galerella and very small species of Urva rather than to Herpestes, Xenogale, and larger species of Urva. The Nakali specimens are more comparable to very small Urva than to Galerella in the retention of small and single-rooted lower first premolar (p1). However, although extant Galerella generally lacks p1, several specimens of extant Galerella retain it. It is noteworthy that Galerella is an African genus, while Urva is an Asian genus. Here, we identified the Nakali specimens as cf. Galerella sp. because they are from Africa, but it should be noted that there is a possibility that they are of Urva or of unknown extinct lineage. This study highlights the problem of the taxonomic identification of fossil dentognathic specimens that were identified as “Herpestes.”