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Skeletal development in sloths and the evolution of mammalian vertebral patterning


Hautier, L; Weisbecker, V; Sánchez-Villagra, M R; Goswami, A; Asher, R J (2010). Skeletal development in sloths and the evolution of mammalian vertebral patterning. Proceedings of the National Academy of Sciences of the United States of America (PNAS), 107(44):18903-18908 + supp. material.

Abstract

Mammals show a very low level of variation in vertebral count, particularly in the neck. Phenotypes exhibited at various stages during the development of the axial skeleton may play a key role in testing mechanisms recently proposed to explain this conservatism. Here, we provide osteogenetic data that identify developmental criteria with which to recognize cervical vs. noncervical vertebrae in mammals. Except for sloths, all mammals show the late ossification of the caudal-most centra in the neck after other centra and neural arches. In sloths with 8–10 ribless neck vertebrae, the caudal-most neck centra ossify early, matching the pattern observed in cranial thoracic vertebrae of other mammals. Accordingly, we interpret the ribless neck vertebrae of three-toed sloths caudal to V7 as thoracic based on our developmental criterion. Applied to the unusual vertebral phenotype of long-necked sloths, these data support the interpretation that elements of the axial skeleton with origins from distinct mesodermal tissues have repatterned over the course of evolution.

Abstract

Mammals show a very low level of variation in vertebral count, particularly in the neck. Phenotypes exhibited at various stages during the development of the axial skeleton may play a key role in testing mechanisms recently proposed to explain this conservatism. Here, we provide osteogenetic data that identify developmental criteria with which to recognize cervical vs. noncervical vertebrae in mammals. Except for sloths, all mammals show the late ossification of the caudal-most centra in the neck after other centra and neural arches. In sloths with 8–10 ribless neck vertebrae, the caudal-most neck centra ossify early, matching the pattern observed in cranial thoracic vertebrae of other mammals. Accordingly, we interpret the ribless neck vertebrae of three-toed sloths caudal to V7 as thoracic based on our developmental criterion. Applied to the unusual vertebral phenotype of long-necked sloths, these data support the interpretation that elements of the axial skeleton with origins from distinct mesodermal tissues have repatterned over the course of evolution.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Uncontrolled Keywords:constraint | heterochrony | vertebrae | ontogeny | Xenarthra
Language:English
Date:2010
Deposited On:13 Jan 2011 16:34
Last Modified:07 Dec 2017 05:49
Publisher:National Academy of Sciences
ISSN:0027-8424
Publisher DOI:https://doi.org/10.1073/pnas.1010335107

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