The first choristoderan record from the Upper Cretaceous of Asia, Tamagawa Formation, Kuji Group, Japan

Abstract

Choristoderes are freshwater diapsid reptiles that are distributed through Laurasia in Jurassic–Miocene deposits. The group shows great diversity in the Early Cretaceous of Asia, with all recognized morphotypes recorded from that region. However, there is then a substantial gap in the Asian record until choristoderes are reported from the Paleocene of Kazakhstan. This gap has raised questions as to whether the group became extinct in Asia during the Late Cretaceous, with subsequent reinvasion from either North America or Europe. Here we report the discovery of vertebrae attributable to Choristodera indet. from the lower Upper Cretaceous (Turonian) of the Tamagawa Formation, Kuji City, Iwate Prefecture, Japan. This is the first record of Choristodera from the Upper Cretaceous of Asia, and may imply that the group persisted in this region from the Jurassic to the Paleocene. The challenge for the future will be to recover a more complete record of Choristodera in the Upper Cretaceous of Asia.