香川県東かがわ市の上部白亜系和泉層群より産出した長頸竜類（爬虫綱，鰭竜目）化石

抄録

Plesiosaur fossils are only scarcely known from the Upper Cretaceous of southwestern Japan. Here, we describe a plesiosaur fossil from the Upper Cretaceous Izumi Group of Kagawa Prefecture, southwestern Japan. The fossil is identified as the diaphysis of a left propodeal, and it belongs to an adult individual because the tuberosity or trochanter is differentiated from the capitulum (sense Brown, 1981). The preaxial margin is concave, and the tuberosity or trochanter is narrow and posteriorly located in dorsal view. This combination is observed in some specimens of the Elasmosauridae and Leptocleidia, but preservation of the described propodial is insufficient to identify even at the family level. Therefore, the specimen is identified as an indeterminate Xenopsaria, which is a clade that include the Elasmosauridae and Leptocleidia. Although fragmentary, the specimen is an important record as the first confirmed adult individual of a plesiosaur recorded in this area.