A comprehensive osteological description of the plesiosaurid Seeleyosaurus

Seeleyosaurus guilelmiimperatoris is an early plesiosauroid from the Lower Jurassic Posidonia Shale of Germany. Although historically important and known from two nearly complete skeletons, its anatomy remained poorly understood. The new study provides a full osteological description of Seeleyosaurus and discusses the taxonomy and phylogeny of early plesiosauroids. Seeleyosaurus is a microcleidid closely related to Microcleidus, and is distinct from Plesiopterys.