MICROSCOPIC DENTAL STRUCTURE IN A POLYCOTYLID PLESIOSAUR (DIAPSIDA: PLESIOSAUROIDEA) FROM THE BOYER BAY MEMBER OF THE SHARON SPRINGS FM., PIERRE SHALE GROUP, SOUTH DAKOTA

Work on the qualitative and quantitative description of dental morphologic variation in fossil reptiles has concentrated heavily on that of theropod dinosaurs, with the goal of identifying shed crowns. In contrast, little attention has been paid to Mesozoic marine reptile taxa, in particular polycotylid plesiosaurs. The teeth of polycotylid plesiosaurs are cone shaped, un-serrated and slightly recurved. The teeth are covered by a series of vertical enamel wrinkles that are more highly developed on the lingual surface of the crown, and decrease in width as they progress toward the apex. Polycotylid crowns are, in all respects other then size, homodont, with little change in shape noticeable between teeth in the anterior vs. posterior portion of the jaw. Some of the most promising research related to reptile tooth morphology, involves the analysis of surface and internal dental microstructure. To date no one has attempted to describe polycotylid dental microstructure beyond simple qualitative observations. This study gives the first overview of polycotylid plesiosaur enamel, dentin and pulp structures through the use of a scanning electron microscope.