Early Pleistocene Fossil Snakes (Reptilia: Squamata) from Okinawajima Island in the Ryukyu Archipelago, Southwestern Japan

摘要

A number of fossil snake vertebrae were collected from Early Pleistocene deposits exposed on a hill surface at Gogayama, Nakijin village, Okinawajima Island, along with many other vertebrate fossils. These represent the oldest fossil records of snakes for the whole Ryukyu Archipelago. We identified each of these fossil snake vertebrae to the lowest taxonomic category possible based on diagnostic features elucidated in our previous study of extant snakes from Japan and adjacent regions. As a result, the vertebrae of at least four genera-Cyclophiops and Dinodon of the family Colubridae, Protobothrops (formerly Trimeresurus) of the family Viperidae, and Sinomicrurus of the family Elapidae-were recognized. Of these, vertebrae identified as belonging to the genus Dinodon were further divided into two distinct forms, although both resembled D. rufozonatum, an extant species that does not presently occur in Okinawajima or any of the surrounding islets in the central Ryukyus. Vertebrae identified as belonging to the other three genera were largely similar to those of the three extant species currently occurring in Okinawajima but with slight differences.