Abstract
Eilenodontines are one of the oldest radiation of herbivorous lepidosaurs (snakes, lizards and tuatara) characterized by batteries of wide teeth with thick enamel that bear mammal-like wear facets. Unlike most reptiles, eilenodontines have limited tooth replacement, making dental longevity particularly important to them. We use both X-ray and neutron computed tomography to examine a fossil tooth from the eilenodontine Eilenodon (Late Jurassic, USA). Of the two approaches, neutron tomography was more successful and facilitated measurements of enamel thickness and distribution. We find the enamel thickness to be regionally variable, thin near the cusp tip (0.10 mm) but thicker around the base (0.15–0.30 mm) and notably greater than that of other rhynchocephalians such as the extant Sphenodon (0.08–0.14 mm). The thick enamel in Eilenodon would permit greater loading, extend tooth lifespan and facilitate the establishment of wear facets that have sharp edges for orally processing plant material such as horsetails (Equisetum). The shape of the enamel dentine junction indicates that tooth development in Eilenodon and Sphenodon involved similar folding of the epithelium but different ameloblast activity.
Highlights
The Rhynchocephalia are today represented by a single living species, the New Zealand tuatara (Sphenodon punctatus), but during the Mesozoic they were diverse and widespread [1,2,3,4,5,6]
The X-ray dataset is inadequate for interpretation of the enamel dentine junction
There is a broad peak between 0.025 and 0.10 which encompasses most of the voxels corresponding to tooth tissues: enamel (0.0191 to approximately 0.0791 with most values above 0.0493), pulp (0.0551 and 0.0837) and dentine
Summary
The Rhynchocephalia are today represented by a single living species, the New Zealand tuatara (Sphenodon punctatus), but during the Mesozoic they were diverse and widespread [1,2,3,4,5,6]. As the earliest referred members are dated to the Late Triassic [11], eilenodontines potentially represent the oldest radiation of herbivorous lepidosaurs (snakes and lizards þ tuatara) They are characterized by deep jaws, broad and closely packed teeth with conspicuous wear facets and unusually thick enamel [7,8]. Their stout teeth possess relatively large bases, apparently suited to withstand high loading and bending forces [1,2,3].
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