RT Journal Article
SR Electronic
T1 Skeletal development in sloths and the evolution of mammalian vertebral patterning
JF Proceedings of the National Academy of Sciences
JO Proc Natl Acad Sci USA
FD National Academy of Sciences
SP 18903
OP 18908
DO 10.1073/pnas.1010335107
VO 107
IS 44
A1 Hautier, Lionel
A1 Weisbecker, Vera
A1 Sánchez-Villagra, Marcelo R.
A1 Goswami, Anjali
A1 Asher, Robert J.
YR 2010
UL http://www.pnas.org/content/107/44/18903.abstract
AB 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.