Discovery of fossil teeth of dogfish, the genus Squalus from the Northern Fossa Magna Region, Nagano Prefecture, central Japan and its significance

Abstract

A few fossil shark teeth were found in the laminated gray mudstone of the lower part of the Middle Miocene (15Ma) Iseyama Formation in Sanada-machi, Ueda-city, Nagano Prefecture, central Japan. These were identified as teeth of dogfish, Squalus sp.indet. This is the first record of the genus Squalus from the Northern Fossa Magna Region in Nagano Prefecture. Judging from the habitat of Squalus and the occurrences of shallow-sea fish fossils, such as Eosardinella hishinaiensis and Family Clupeidae, it is estimated that the sea which deposited the lower part of the Iseyama Formation was the continental or insular shelf and from shelf edge to shelf slope which was fell sharply from the shallow sea of coastal or bay zone with surface warm current.