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Abstract Tusks are ever‐growing teeth present in mammals of the clade Paenungulata. Unlike the perpetually growing incisors of rodents, tusks are not used in mastication, and in at least some paenungulatans, the tusk is composed of dentin alone in adults. Few studies have provided tissue‐level information on tusks of adult paenungulatans with embedding techniques that identify epithelial and other soft tissues. In order to examine the mineralized tissues as well as the cells that form teeth, we studied a single, subadult rock hyrax (Procavia capensis) using microCT and paraffin histology with traditional staining as well as RUNX2 immunohistochemistry, and compared its teeth to scans of adult hyraxes. Three‐dimensional reconstructions from microCT volumes revealed that the tusk of this specimen is the only fully erupted replacement tooth, the first adult premolar (P1) is starting to erupt, and the first permanent molar (M1) is fully erupted, whereas all other replacement teeth and M2 remain in crypts. The tusk has a thin layer of enamel on its dorsal side; this is confirmed by histology. All deciduous premolars still possess roots that are in the process of resorption. Amelogenesis has progressed to maturation or nearly so in P1–P3. Notable histological characteristics of replacement premolars include the lack of a stellate reticulum in all except P4, and expression of RUNX2 in ameloblasts, a marker which is expressed by ameloblasts at all stages of amelogenesis. Since the pulp chambers of replacement premolars are relatively large compared to adults, a lengthy time in crypts may be important for dentin production. The results confirm that the hyrax has thin enamel on tusks, supporting the hypothesis that enamel is of limited importance for non‐feeding behaviors.
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The significance of enamel thickness in the teeth of Alligator mississippiensis and its diversity among crocodyliforms
Abstract Enamel is the hardest tissue in the vertebrate body. Although variation in enamel microstructure is often linked with diet, the gross proportions of the tissues that compose vertebrate teeth remain relatively unexplored in reptiles. To investigate the patterns of enamel thickness in crocodyliforms, we used micro‐computed tomography scanning to evaluate enamel thickness in teeth ofAlligator mississippiensisfrom rostral, intermediate and caudal locations in the tooth row from an ontogenetic range of animals. We also evaluated enamel thickness in the derived teeth of several extinct crocodyliforms with disparate craniodental morphologies. Our data show that enamel thickness scales isometrically with skull length. We also show that enamel is relatively thicker in caudal teeth than teeth in more rostral positions, concordant with the higher bite forces they experience during feeding. We compared our data with existing enamel thickness data reported from dinosaurs and mammalian taxa to find that archosaurs have markedly thinner enamel than most mammals. These findings serve as a basis for future investigations into the diversity and function of the proportions of dental tissues.
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- Award ID(s):
- 1631684
- PAR ID:
- 10360468
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Zoology
- Volume:
- 309
- Issue:
- 3
- ISSN:
- 0952-8369
- Page Range / eLocation ID:
- p. 172-181
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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