Fossils reveal the complex evolutionary history of the mammalian regionalized spine

A unique characteristic of mammals is a vertebral column with anatomically distinct regions, but when and how this trait evolved remains unknown. We reconstructed vertebral regions and their morphological disparity in the extinct forerunners of mammals, the nonmammalian synapsids, to elucidate the evolution of mammalian axial differentiation. Mapping patterns of regionalization and disparity (heterogeneity) across amniotes reveals that both traits increased during synapsid evolution. However, the onset of regionalization predates increased heterogeneity. On the basis of inferred homology patterns, we propose a “pectoral-first” hypothesis for region acquisition, whereby evolutionary shifts in forelimb function in nonmammalian therapsids drove increasing vertebral modularity prior to differentiation of the vertebral column for specialized functions in mammals.


Publication Date:
Sep 21 2018
Date Submitted:
Jul 10 2019
ISSN:
0036-8075
Citation:
Science




 Record created 2019-07-10, last modified 2019-07-12

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