Crocodyliformes, such as gobiosuchids, goniopholidids, paralligatorids, and eusuchians, have widely distributed in East Asia during the Cretaceous. In Japan, the Futaba Group in Fukushima Prefecture is one of the most significant Cretaceous outcrops that have produced terrestrial vertebrate fossils, including dinosaurs. However, a definitive crocodyliform has never been reported from Futaba ... [Show full abstract] Group. Here we report a crocodyliform osteoderm from the Tamayama Formation (Coniacian–Santonian) of the Futaba Group. The osteoderm is rectangular, wider than long, and bears a tall keel, which can be identified as a dorsal paravertebral osteoderm. A comparison with other crocodyliforms suggests that it pertains to semi-aquatic Neosuchia, but not to Goniopholididae or Paralligatoridae. The first definitive record of a semi-aquatic, derived neosuchian (e.g., eusuchians) from the Futaba Group indicates their appearance before the Coniacian age in East Asia.