Futabasaurus is a genus of plesiosaur from the Late Cretaceous of Fukushima, Japan. Described and named in 2006, it was assigned to the family Elasmosauridae. The length was about 7 m, and the weight was about 3~4 tons. Futabasaurus is the first elasmosaurid found in Japan. The type species is F. suzukii. Many of the bones of the type specimen show apparent scavenging or predation by sharks.
Cast of fossils of Futabasaurus suzukii exhibited at the National Science Museum of Japan.The name "Futabasaurus" also appears in connection with a theropod dinosaur, also from the Late Cretaceous of Japan. However, this dinosaur was not officially named, so the dinosaur "Futabasaurus" is a nomen nudum when applied to this theropod. It is not the same as the plesiosaur named Futabasaurus.
The first fossils of Futabasaurus were found in the Irimazawa Member of the Tamayama Formation, Futaba Group, Fukushima Prefecture, Japan, dating to the Inoceramus amakusensis zone of the early Santonian. The fossils were found by Tadashi Suzuki, a high school student around that time.