Taxonomic Revision of Lower Miocene Pecorans (Mammalia, Artiodactyla) from Japan, with a New Fossil Record of Stem Cervidae

Abstract

The origin and early dispersion of crown groups (e.g. Cervidae and Bovidae) in pecorans are traced back to the late Oligocene or early Miocene in Eurasia. The fossil pecorans from the lower Miocene of Japan are highly fragmentary but form evidence of a zoogeographic connection between Japan and the Eurasian continent during this period. In this study, we describe dental fossils (seven specimens) from five Burdigalian formations (Nakamura Fm. ∼18.5 Ma; Hiramaki Fm. ∼18 Ma; Misawa Fm. and Kitatage/Asakawa Fm. ∼17 Ma; Kunimi Fm. ∼16 Ma), and as a result of taxonomic revision we recognize four species, including a basal species of Cervidae, Dicrocerus? tokunagai, cf. Palaeomeryx minoensis, and Amphimoschus sp. These species have the basic occlusal patterns of cheek teeth inherited from primitive pecorans (e.g. Amphitragulus), but each species displays advanced characteristics, such as full selenodonty, a weak/no external postprotocristid, and a bicuspidate third lobe of m3 (Amphimoschus). The early group of crown pecorans composed of basal cervids (Lagomerycinae or Procervulinae), Palaeomeryx s.l., and Amphimoschus, had dispersed widely in Europe (early Orleanian or MN3) and East Asia (Shanwangian), including Japan. Our findings on the Japanese fossil records demonstrate that the dispersion of a basal cervid and palaeomerycid between Japan and the Eurasian continent had been completed before 18 Ma. Further studies with additional material would reveal detailed taxonomic relationships and evolutionary process of the Japanese pecorans in the Burdigalian.