Crocodyliform remains from the Upper Cretaceous (Turonian) Tamagawa Formation, northeastern Japan with preliminary dietary reconstruction through dental microwear texture analysis

Abstract

Here we describe recently recovered crocodyliform remains from the Tamagawa Formation of Kuji Group, Kuji city, northeastern Japan. The material comprises osteoderms, vertebrae, a frontal bone, and isolated teeth. The dorsal paravertebral osteoderms bear a sagittal keel on the posterior half of the element, extending to its caudal margin, which indicates the presence of paralligatorids within the Kuji crocodyliform assemblage. Further, the Kuji crocodyliform assemblage may have consisted of multiple taxa, as the frontal bone lacks the sagittal keel characteristic of paralligatorids. Contemporaneous paralligatorids have been reported from Northeastern China, Mongolia, and Uzbekistan. The discovery of a potential paralligatorid from Kuji, Japan, suggests that paralligatorids were widely distributed across Asia, from coastal to inland regions, during the Late Cretaceous. Furthermore, potential diets of taxa included in the crocodyliform assemblage from Kuji were estimated through dental microwear texture analysis. The dental microwear texture observed in Kuji specimens is distinct from that of piscivorous and small crocodylians (skull length <20 cm), while comparable to that of large crocodylians consuming hard-objects (skull length >20 cm). Considering the existence of a medium-sized species (3 m total length) in the crocodyliform assemblage from Kuji, their diet probably included mid to large sized tetrapods, such as turtles and dinosaurs.