A new species of Stacheoceras (Permian ammonoid) from the Upper Permian in the South Kitakami Belt, Northeast Japan

Abstract

Stacheoceras Gemmellaro is a well known, globally distributed genus of Permian ammonoids ranging from the Artinskian to Changhsingian (Kullmann et al., 2000) or from the Kungurian to Changhsingian (Leonova, 2002). Over 50 species of the genus have hitherto been known worldwide, almost all of which are rather small in size, with diameters less than 10 cm. Only two species, Stacheoceras xiukangense Sheng and S. raridentatum Sheng from Xizang, southwest China, attain a diameter over 10 cm (Sheng, 1984, 1988). The following taxa of Stacheoceras, all regularsized, have been reported from the Wordian to Changhsingian strata of the South Kitakami Belt, Northeast Japan: Stacheoceras aff. grunwaldti Gemmellaro (Hayasaka, 1965), S. iwaizakiense Mabuti (Mabuti, 1935; Ehiro and Bando, 1985), S. otomoi Ehiro, Shimoyama and Murata (Ehiro et al., 1986), S. cf. trimulti Diener (Working Group on the PermianTriassic Systems, 1975) and S. sp. (Hayasaka, 1940; Koizumi, 1975; Ehiro et al., 1986; Ehiro and Araki, 1997; Ehiro, 2001). Recently a considerably large specimen of Stacheoceras was recovered from the Upper Permian of South Kitakami Belt, Northeast Japan. It has also a more complex external suture line than all the previously known species. This paper describes it as a new species, Stacheoceras giganteum sp. nov. Stacheoceras giganteum sp. nov. was collected by Hitoshi Hasegawa from a calcareous nodule included in mudstone of the lower part of the Suenosaki Formation exposed along the Pacific coast of Ishihama, Minamisanriku-cho (former Utatsu-cho), Motoyoshigun, Miyagi prefecture. The fossil locality is the same as Loc. 3 of Utatsu district in Ehiro and Bando (1985) and yields such ammonoid fossils as Stacheoceras iwaizakiense Mabuti, Timorites intermedium (Wanner), Pseudogastrioceras sp., Araxoceras cf. rotoides Ruzhentsev, A. sp., Vescotoceras japonicum (Bando and Ehiro), V. sp., Dzhulfoceras cf. furnishi Ruzhentsev (Ehiro and Bando, 1985; Ehiro et al., 1986; Ehiro, 2001). Based on these ammonoids, especially on the occurrence of Pseudogastrioceras, Araxoceras, Vescotoceras and Dzhulfoceras, the fossil horizon of the lower part of the Suenosaki Formation is correlatable with the Upper Permian Wuchiapingian (Ehiro and Bando, 1985; Ehiro, 2001)