The hidden teeth of sloths: evolutionary vestiges and the development of a simplified dentition

Xenarthrans are unique among mammals in retaining simplified teeth that are rootless and homodont, which makes it difficult to determine dental homologies. We apply computerized tomography to prenatal developmental series of extant sloths, Bradypus and Choloepus , to further elucidate the patterns o...

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Bibliographic Details
Published in:Scientific reports 2016-06, Vol.6 (1), p.27763-27763, Article 27763
Main Authors: Hautier, Lionel, Gomes Rodrigues, Helder, Billet, Guillaume, Asher, Robert J.
Format: Article
Language:English
Subjects:
631/136/1455
631/181/414
Adults
Animal biology
Animals
Biological Evolution
Dentition
Humanities and Social Sciences
Imaging, Three-Dimensional
Life Sciences
Mammals
Mineralization
Morphology
multidisciplinary
Palate - anatomy & histology
Science
Sloths - anatomy & histology
Teeth
Tomography, X-Ray Computed
Tooth - anatomy & histology
Tooth - embryology
Vertebrate Zoology
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Summary:Xenarthrans are unique among mammals in retaining simplified teeth that are rootless and homodont, which makes it difficult to determine dental homologies. We apply computerized tomography to prenatal developmental series of extant sloths, Bradypus and Choloepus , to further elucidate the patterns of morphological variation in their dentition. We also propose new criteria based on sequences of dental mineralization and the presence of vestigial teeth, to distinguish between caniniforms and postcaniniforms. We report for the first time the presence of vestigial incisors in Bradypus . We also show the presence of a vestigial tooth in front of the lower caniniform in both extant sloth genera and the existence of two generations for the upper caniniform in Choloepus . The study of their sequence of mineralization indicates that the lower and upper caniniform teeth are not homologous in sloths and suggests that upper caniniforms are not homologous between the two extant sloth genera. Our results show that assessing the developmental processes and functional constraints remains crucial to understand the dental variations observed in sloths and more generally, tooth class homology issues in mammals. Applied to the tooth row of all extinct sloths, these developmental data illuminate a potentially ancestral dental formula for sloths.
ISSN:2045-2322
2045-2322
DOI:10.1038/srep27763