Cenomanian-Turonian Occurrences of Plesiosaurs (Reptilia: Plesiosauria) in Kansas, USA, and Their Abundance and Ecological Context in the Late Cretaceous Western Interior Seaway

Plesiosaurs are a clade of Mesozoic marine reptiles with diverse forms occupying different niches globally throughout the Jurassic and Cretaceous periods. This study focuses on historical and newly identified occurrences of Plesiosauria (partial skeletons and isolated teeth) from the late Cenomanian-Turonian Western Interior Seaway deposits of the ‘Fort Benton Group’ (Graneros Shale, Greenhorn Limestone, and Carlile Shale). Cenomanian-Turonian plesiosaurs are especially numerous in Kansas, USA, providing basic insight about plesiosaur abundance, diversity, and preferred habitats in the seaway. Skeletal elements and partial skeletons identifiable to a family level are considered a reflection of populations in space and time. However, some isolated (shed) teeth are considered because they provide novel stratigraphic information for particular plesiosaur subgroups. With a total of 40 partial skeletons from the ‘Fort Benton interval’ of Kansas, this study demonstrates that polycotylids are the most abundant plesiosaur morphotype (65% of records), and nearly all polycotylids occur in open marine, deeper water phases of the Greenhorn Limestone and the Fairport Chalk Member, Carlile Shale. Pliosauridae (20% of records) are relatively rare but have the most diverse environmental distribution (presence in all formations) and likely do not exist beyond Turonian time. Elasmosauridae (15% of records) are the rarest morphotype with few records from open marine carbonate environments, and well-constrained stratigraphic occurrences are mainly from nearshore/shoreface environments.