Fig. 1. A in Dimorphism in tetragonitid ammonoid Tetragonites minimus from the Upper Cretaceous in Hokkaido, Northern Japan

Fig. 1. A. Location map around studied areas in Hokkaido, Japan (inset shoving location of Yezo Group deposits). B. Generalized columnar section of the Santonian, Yezo Group in the Kotanbetsu area showing stratigraphic occurrence of dimorphic pairs of Tetragonites minimus Shigeta, 1989, and the selected stage-diagnostic mega-fossils. Double head arrows indicate the areas where the columnar sections were constructed. See Aiba (2019) for details of stratigraphy. Abbreviations: C., Creek; R., River.