INTRODUCTION

Small mammal fossils from the Tertiary were extremely rare in Japan until recently. Following the first discovery of an eomyid jaw with p4 and an isolated m1 in 1989 (Tomida and Setoguchii 1994), more than 40 insectivore, lagomorph, and rodent specimens have been found from a locality on the left bank of Kiso River at Dota, Kani City, central Japan. Originally these specimens were collectively called the Dota local fauna, but because the term local fauna has not been favored recently, this assemblage is simply called the Dota fauna here. Although eight taxa of small mammals have been identified in the Dota fauna (Tomida 2000), the majority of the specimens have remained undescribed, except for the beaver Youngofiber (Tomida et al. 1995). The present paper describes Megapeomys, which is one of those eight taxa. It is represented by only one isolated tooth. It was referred to Megapeomys sp. by Fejfar et al. (1998), but now direct comparison with the material of M. lavocati has confirmed distinction of the Japanese species from the Czech species.

For dental morphology, the nomenclature of Engesser (1990) and Fejfar et al. (1998) is used.