• plesiosaur;
  • elasmosaur;
  • Japan;
  • Cretaceous;
  • taphonomy;
  • biogeography;
  • biostratigraphy

Abstract:  A new genus and species of an elasmosaurid plesiosaur, Futabasaurus suzukii, is described based on a partial skeleton from the Inoceramus amakusensis Zone (Lower Santonian, Upper Cretaceous) of the Irimazawa Member of the Tamayama Formation, Futaba Group, in Fukushima Prefecture, Japan. The new taxon is characterized by a number of characters such as the wide space between the orbit and external naris, posterior extension of the interclavicle, relatively long humerus and prominent femoral muscle scar. The holotype includes a partial skull and mandible, posterior cervicals to sacrals, ribs, clavicular arch, pelvic girdle and four limbs. The remains are mostly in articulation, and exhibit evidence of predation/scavenging by sharks. The distribution of elasmosaurid species in the circum-Pacific region remains unclear due to the lack of diagnostic materials. The occurrence of F. suzukii is geographically and stratigraphically significant, because it allows species-level comparison; as a diagnosable elasmosaurid specimen, F. suzukii is the first and the oldest from the northern Pacific.