Thirty-seven species of Campanian (Late Cretaceous) ammonoids, which includes three newly described species (Neophylloceras nodosum sp. nov., Menuites armatus sp. nov. and Parasolenoceras ribiraense sp. nov.), and four species of inoceramid bivalves are reported from the Urakawa and Chinomigawa formations of the Yezo Group in the Ribira River area, southern central Hokkaido, Japan. As brief summary of the stratigraphy and paleontology of the Urakawa and Chinomigawa formations is provided. Furthermore, seven distinct Campanian ammonoid and inoceramid assemblages are recognized as follows, in ascending order: the lower Campanian Gaudryceras tenuiliratum beds, the middle Campanian Sphenoceramus orientalis beds, Sphenoceramus schmidti beds and Metaplacenticeras subtilistriatum beds, and the lower upper Campanian Baculites pacificus beds, Baculites subanceps beds and Baculites rex beds. Pachydiscus excelsus is reported from the middle Campanian Metaplacenticeras subtilistriatum beds as well as the lower upper Campanian, thus making it the oldest Pachydiscus in the Northwest Pacific region. Since Pachydiscus flourished in other regions during early Campanian time, its occurrence in the Ribira River area suggests that the genus extended its geographical distribution from other regions to this particular area during middle Campanian time.

Shigeta, Yasunari. Campanian (Late Cretaceous) ammonoids and inoceramids from the Ribira River area, Hokkaido, northern Japan / Y. Shigeta, M. Izukura, T. Nishimura. – Tokyo : National museum of nature and science, 2019 - (National museum of nature and science monographs / National museum of nature and science (Tokyo) ; N 50).Bibliogr.: p. 129-136.