A late middle jurassic boreal belemnite cylindroteuthis from central japan and its paleobiogeographic implications

A single rostrum of Cylindroteuthis (Cylindroteuthis) cf. theofilaktovi Nikitin recovered from the Late Bathonian-Early Callovian Kaizara Formation of the Tetori Group in Shimoyama, Kuzuryu area, Central Japan, is described for the first time in East Asia. This belemnite species has been previously known only from the Early Callovian of Central Ukraine in Eastern Europe. Since the family Cylindroteuthididae has been considered as the typical Boreal or northern element in the Jurassic belemnite paleobiogeographic studies, its occurrence in the Inner Zone (Japan Sea side) of Southwest Japan clearly indicates that Cylindroteuthis expanded its distribution to the mid-latitudes of the Northwest Pacific at that time. This expansion possibly corresponds to the Early Callovian spread of boreal cylindroteuthids toward south into Europe in the Boreal-Atlantic seas. The occurrence of Cylindroteuthis from the Kaizara Formation strongly suggests that a cooler current possibly from the Arctic reached the Tetori Basin in the Late Bathonian-Early Callovian time.