Article: Palaeoecological analysis of ammonoid assemblages in the Turonian Scaphites facies of Hokkaido, Japan

Palaeoecological analysis of ammonoid assemblages in the Turonian (Cretaceous) Scaphites facies of Hokkaido has yielded quantitative data on distribution, mode of occurrence, and preservation of many species. The results show that most collignoniceratids, acanthoceratids, and heteromorphs in the region are autochthonous in a broad sense; the litho- and biofacies in which these groups occur suggest that the first two lived in inshore to near-shore shallow waters, and the latter in nearshore to offshore more or less deep waters. Post-mortem transportation or drift might be important as a factor in distribution of thanatocoenoses of the phylloceratids, tetragonitids, and desmoceratids; therefore their habitats could not be determined from the analysis of assemblages. Examination of relative siphuncular strength in many well-preserved specimens of twelve species suggests that the depth limits of the tetragonitids, phylloceratids, and desmoceratids may have been much greater than those of other groups.