日本の恐竜研究はどこまできたのか?：東・東南アジアの前期白亜紀フォーナの比較

抄録

Researches on Japanese dinosaurs make progress dramatically in these decades, since the first dinosaur discovery in the present territory of Japan was made in 1978. Currently, Japanese dinosaur fossils have been unearthed in 16 prefectures of Japan, from Hokkaido to Kagoshima. However, all named Japanese dinosaurs, seven original genus and species, are known only from three localities of the Lower Cretaceous of the Inner Zone of Southwest Japan; Kuwajima and Kitadani formations of the Tetori Group in Ishikawa and Fukui respectively, and “lower formation” of the Sasayama Group in Hyogo. Abundant dinosaur body fossil records from these sites make it possible to compare and discuss as a dinosaur assemblage, namely “Dinosaur Fauna (hereafter DF)”, to other Early Cretaceous DFs in East and Southeast Asia. Comparisons of Shiramine (Kuwajima Fm.), Katsuyama (Kitadani Fm.) and Tamba-Sasayama (“lower formation”) DFs to Hekou, Jehol and Mazongshan DFs from China (North China Craton) and Khorat DF from Thailand (Indosina Terrane) shows interesting results on relationships among faunal changes, paleogeography and paleoenvironment; Shiramine and Jehol DFs, in the early Early Cretaceous, shares faunal similarities under a relatively cool climate, Katsuyama DF, in the middle Early Cretaceous, became to include “southern”-type dinosaurs, such as an allosauroid and a hadrosauroid under somewhat dry and temperate climate, and Tamba-Sasayama DF, in the late Early Cretaceous, includes a neoceratposian shared with Mazongshan DF and sauropod with “peg” like teeth shared with Khorat DF under seasonal dry and temperate climate. Although more sophisticated chronological, paleogeographical, and paleoenvironmental data are needed to understand their relationships, our result implies that there were possibly several routes for dinosaur divergences in the eastern margin of Asia continent, and some taxa might have been originated in the Early Cretaceous of Asia.