The oldest Asian Sivaonyx (Lutrinae, Mustelidae): a contribution to the evolutionary history of bunodont

Abstract

We describe here specimens of the otter Sivaonyx cf. gandakasensis from the late Middle Miocene hominoid-bearing basin of Chiang Muan, northern Thailand. Asian Sivaonyx species were previously recorded in the Late Miocene of the Siwalik Hills and Southern China. The new Thai remains could constitute the oldest occurrence of the genus in Asia (12.4-12.2 m.y.) and, more generally, in the Old World. S. gandakasensis, also occurring in the early Late Miocene and possibly Middle Miocene deposits of the Siwalik Hills, is the most primitive species of the genus. Based on the m1 morphology, we suggest a close relationship of this species with S. hessicus from the Late Miocene of Europe. In this study, we discuss the primitive morphological characters of Eurasian Sivaonyx compared to African ones, using notably the previously unknown M1 of S. cf. gandakasensis (e.g., developed M1 parastyle, high protoconid and narrow talonid basin on m1). Moreover, S. bathygnathus, the third and most derived Eurasian species known from the Late Miocene of the Siwaliks and Southern China, seems to be the most probable ancestor of Mio-Pleistocene African Sivaonyx. We therefore propose a dispersal of Sivaonyx from Asia to Africa during the Late Miocene, probably between ca. 10 and 7 m.y.