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New Paper on mosasaur tooth histology and character terminology


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Authors: Hallie P. Street, Aaron R. H. LeBlanc, and Michael W. Caldwell


Abstract: Mosasaur researchers have used varieties of tooth crown ornamentation as diagnostic and phylo-genetic characters for decades. Such tooth crown features include facets, flutes, striations, serrated carinae, and coarse anastomosing texture. This study investigates the relative contributions of dentine and enamel to the development of these dental characters and assesses homology statements between these structures. Histological analysis of isolated mosasaur teeth reveals that flutes and facets develop initially from the den-tine, and the external enamel morphology we observe macroscopically mirrors the shape of the underlying dentine. Striations combine underlying contributions from the dentine with additional and irregular en-amel deposition resulting strictly from amelogenesis. In both serrated carinae and anastomosing texture the Dentine-Enamel Junction is smooth, and these external ornamentations form exclusively through variations in enamel development. Based on these observations, we infer that flutes and facets form a morphological spectrum and should not be treated as separate phylogenetic characters. Conversely, striations develop differ-ently than flutes and facets, and should therefore be treated as a distinct character. We recommend referring to serrations on mosasaur carinae as false denticulations to differentiate these enamel-only structures from true denticles possessing a dentine core. Anastomosing texture can also coincide with significant apical en-amel thickening, both of which could be adaptations for processing harder prey, as they are in modern rep-tiles. Care must be taken when using tooth crown features as diagnostic or phylogenetic characters because seemingly different morphologies can have similar developmental origins, and tooth morphology can be more closely tied to diet than common ancestry. 

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