A new large beaver (Mammalia, Castoridae) from the early Miocene of Japan

ABSTRACT

A new early Miocene large castorid, Minocastor godai gen. et sp. nov., from the Dota locality, Gifu Prefecture in central Japan, is described on the basis of dentaries and teeth. The material comes from the Kani basin, where limnofluviatile clay and sandstones of the Nakamura Formation (Mizunami Group) are exposed on the southern (left) bank of the Kiso River. It represents the richest sample of a Miocene small mammal in the Japanese fossil record thus far known. Based on jaw and tooth morphology, this new castorid most likely represents a primitive anchitheriomyine. However, it lacks the marked striations on the incisors that are characteristic of the advanced large, middle Miocene anchitheriomyines like Anchitheriomys and Amblycastor. The new castorid shares this dental feature with other primitive anchitheriomyines from Asia and North America, like Propalaeocastor, Oligotheriomys, and Miotheriomys. For these genera, a new tribe, Minocastorini, is proposed as sister group to the Anchitheriomyini. The incisor enamel microstructure of the new castorid largely exhibits plesiomorphic characters but also apomorphic features such as pseudo-pauciserial Hunter-Schreger bands. Additionally, the outer portion of the enamel band is rather thick in comparison to that of other beavers. Based on the rodent taxa associated with Minocastor godai gen. et sp. nov., Dota can be correlated with European Neogene mammal units MN 3/4. Magnetostratigraphic studies and radiometric dates obtained from the Mizunami Group indicate that Dota is more likely correlated with MN 3, with an absolute age of around 18.5 Ma.

http://zoobank.org/urn:lsid:zoobank:org:pub:B1886424-1759-4BDA-A5CC-D122436E1A76

Citation for this article: Mörs, T., Y. Tomida, and D. C. Kalthoff. 2016. A new large beaver (Mammalia, Castoridae) from the early Miocene of Japan. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1080720.

ACKNOWLEDGMENTS

We are indebted to T. Goda, who generously donated these important specimens to NMNS, Japan, and who guided us in the field and provided us with all information regarding their provenance. We are grateful to M. Oshima for artwork, to H. Vårdal for photographs, and to T. Topper for correcting the English language. The helpful comments of the referees W. W. Korth and J. X. Samuels as well as the handling editor M. Sánchez-Villagra are kindly acknowledged. TM was financially supported by The Royal Swedish Academy of Sciences (KVA, Stockholm, Sweden) and by the Japan Society for the Promotion of Science (JSPS, Tokyo, Japan). DCK acknowledges the Deutsche Forschungsgemeinschaft (DFG, Bonn, Germany) for various grants to study mammalian enamel microstructure.