Scanning electron microscope analysis of enamel microstructure in a Polycotylid (Plesiosauria) from the Pierre Shale Group, South Dakota, U.S.A.

Abstract

Shale Group, South Dakota, U.S.A.The teeth of polycotylid plesiosaurs are generally simple, cone shaped, non-serrated and only slightly recurved without distinct carinae. The surface of crowns are characterized by a series of vertical enamel wrinkles that are more highly developed on the lingual surface of the crown, and decrease in width and number toward the apex. Some of the most promising research related to fossil dentition, involves the analysis of surface and internal dental microstructure. This study, is an attempt to examine and describe polycotylid dental microstructure. It gives an overview of polycotylid plesiosaur enamel and dentine microstructures using a scanning electron microscope. Enamel type and structures vary, based on its position on the surface of the crown, and its perceived strength requirements.The dentition layer is "honeycombed" with tubular structure, possibly to provide nourishment to fast growing crowns. The study of crown microstructures may lead to a better understanding of polycotylid niche preference in the late Cretaceous oceans. The teeth of polycotylid plesiosaurs are generally simple, cone shaped, non-serrated and only 10 slightly recurved without distinct carinae. The surface of crowns are characterized by a series of vertical 11 enamel wrinkles that are more highly developed on the lingual surface of the crown, and decrease in 12 width and number toward the apex. Some of the most promising research related to fossil dentition, 13 involves the analysis of surface and internal dental microstructure. This study, is an attempt to examine 14 and describe polycotylid dental microstructure. It gives an overview of polycotylid plesiosaur enamel and 15 dentine microstructures using a scanning electron microscope. Enamel type and structures vary, based on 16 its position on the surface of the crown, and its perceived strength requirements. The dentition layer is 17 "honeycombed" with tubular structure, possibly to provide nourishment to fast growing crowns. The 18 study of crown microstructures may lead to a better understanding of polycotylid niche preference in the 19 late Cretaceous oceans. 20 Introduction 21The study of enamel microstructure of both fossil and extant amniote taxa has been extensively 22 studied (Koenigswald and Sander 1997;Sander 2000; Hwang 2005; Stokosa 2005 The teeth of polycotylid plesiosaurs are cone shaped, un-serrated and slightly recurved. The 40 crowns are covered by a series of vertical enamel wrinkles that are more highly developed on the lingual 41 surface of the crown, and decrease in width as they move toward the apex (Figures 2 and 3). Polycotylid 42 crowns are, in all respects other than size, homodont, with little change in shape noticeable between teeth 43 in the anterior vs. posterior portion of the jaw. 44 Materials and Methods 45The specimen (SDSM 86604) Memorial Museum in Deadwood, South Dakota. Crowns from this specimen were measured and 53 described for morphology, but were not available for Scanning Electron Microscope (SEM) analysis....