Deep-sea elasmobranch fauna with the first descriptions of genera Arynchobatis and Pseudoraja from the Miocene Yatsuo group in Toyama, central Japan

Abstract

ABSTRACT Herein, we describe 22 deep-sea elasmobranch species of the early to middle Miocene Yatsuo Group found in central Japan. The deep-sea elasmobranch fauna of the Yatsuo Group comprises various Squaliformes species together with a few scyliorhinid members and batoids species. This study represents the first fossil record of the occurrence of Arhynchobatis and Pseudoraja. The Yatsuo fauna is divided into three assemblages: Kurosedani Formation, lower Higashibessho Formation, and upper Higashibessho Formation assemblages. The Kurosedani Formation and upper Higashibessho Formation assemblages include many Squalus but only few Squaliolus species, and scyliorhinids. The lower Higashibessho Formation assemblage comprises many Squaliolus species, but only few Squalus species. Squalus species inhabit in shallower deep sea, unlike other genera occurring in the Yatsuo Group, and also it is more frequent in the horizon deposited in the shallower deep-sea than in the other horizons. The frequency of demersal scyliorhinids decreases in the dysoxic environment at the bottom layer. Occurrence of the tropical-subtropical batoid species of Pseudoraja and Benthobatis indicates subtropical palaeoenvironments in central Japan during the early to middle Miocene. At present, species of these two genera are not distributed in areas surrounding Japan.