Dental histology of Coelophysis bauri and the evolution of tooth attachment tissues in early dinosaurs

Abstract

Studies of dinosaur teeth have focused primarily on external crown morphology and thus, use shed or in situ tooth crowns, and are limited to the enamel and dentine dental tissues. As a result, the full suites of periodontal tissues that attach teeth to the jaws remain poorly documented, particularly in early dinosaurs. These tissues are an integral part of the tooth and thus essential to a more complete understanding of dental anatomy, development, and evolution in dinosaurs. To identify the tooth attachment tissues in early dinosaurs, histological thin sections were prepared from the maxilla and dentary of a partial skull of the early theropod Coelophysis bauri from the Upper Triassic (Rhaetian- 209-201 Ma) Whitaker Quarry, New Mexico, USA. As one of the phylogenetically and geologically oldest dinosaurs, it is an ideal candidate for examining dental tissues near the base of the dinosaurian clade. The teeth of C. bauri exhibited a fibrous tooth attachment in which the teeth possessed five tissues: enamel, dentine, cementum, periodontal ligament (PDL), and alveolar bone. Our findings, coupled with those of more recent studies of ornithischian teeth, indicate that a tripartite periodontium, similar to that of crocodilians and mammals, is the plesiomorphic condition for dinosaurs. The occurrence of a tripartite periodontium in dinosaurs adds to the growing consensus that the presence of these tissues is the plesiomorphic condition for the major amniote clades. Furthermore, this study establishes the relative timing of tissue development and growth directions of periodontal tissues and provides the first comparative framework for future studies of dinosaur periodontal development, tooth replacement, and histology. J. Morphol. 277:916-924, 2016. © 2016 Wiley Periodicals, Inc.

Mosasaurs and snakes have a periodontal ligament: timing and extent of calcification, not tissue complexity, determines tooth attachment mode in reptiles

“…; Fong et al. ; García & Zurriaguz, ; LeBlanc et al. ,b), further emphasizing the evolutionary conservatism in amniote tooth attachment tissues.…”

“…; Fong et al. ) thecodonty is a geometric term related to the amount of bony support around a tooth, whereas tooth attachment describes the degree of calcification of the tooth to the jaw. Thecodonty displays extensive homoplasy across Amniota (Dumont et al.…”

Description of Tooth Ontogeny and Replacement Patterns in a Juvenile Tarbosaurus bataar (Dinosauria: Theropoda) Using CT‐Scan Data

“…The present study provides the first quantitative estimation of the relative time intervals of tooth replacement stages in a theropod and as well as in various crocodilians. The data on MPC‐D 107/7 Tarbosaurus bataar was consistent with the interpretations made in previous studies (Edmund, ; Fong et al, ; LeBlanc et al, ) that replacement teeth spend much formative time and grow to large sizes outside of the pulp cavity of their predecessors. In MPC‐D 107/7, Stages i–iii combined occupied 38% of the tooth life span whereas Stages iv and v combined took up 12% of it (Fig.…”

“…In addition, the value of the Stages i–iii combined in MPC‐D 107/7 was greater than those found in the crocodilians examined here. In extant crocodilians, especially Alligator mississippiensis , in contrast, much of the formative time has been considered to occur within the pulp cavity of the predecessor (Edmund, , , ; Fong et al, ; LeBlanc et al, ). The relative time intervals estimated here, however, show that the percentages of Stages iv and v combined varied greatly among the examined crocodilians.…”

Osteopontin regulates dentin and alveolar bone development and mineralization

“…This question, while both clinically relevant and critical to understanding the basic biology of the periodontium, may also lie at the heart of the evolution of the periodontium (tooth in socket, or gomphosis joint), as the ability to promote and restrict mineralization in a site-specific fashion would be key for creating and maintaining these hard-soft interfaces. This evolutionary concept is supported by studies pointing to an ancient origin of cementum and documenting variable regulation of periodontal mineralization in extinct and extant species [17–21]. …”