Data from: Phenotypic integration in the carnivoran backbone and the evolution of functional differentiation in metameric structures

Explaining the origin and evolution of a vertebral column with
anatomically distinct regions that characterizes the tetrapod body plan
provides understanding of how metameric structures become repeated and how
they acquire the ability to perform different functions. However, despite
many decades of inquiry, the advantages and costs of vertebral column
regionalization in anatomically distinct blocks, their functional
specialization, and how they channel new evolutionary outcomes are poorly
understood. Here, we investigate morphological integration (and how this
integration is structured [modularity]) between all the presacral
vertebrae of mammalian carnivorans to provide a better understanding of
how regionalization in metameric structures evolves. Our results
demonstrate that the subunits of the presacral column are highly
integrated. However, underlying to this general pattern, three sets of
vertebrae are recognized as presacral modules –the cervical module, the
antero-dorsal module, and the postero-dorsal module– as well as one weakly
integrated vertebra (diaphragmatic) that forms a transition between both
dorsal modules. We hypothesize that the strength of integration organizing
the axial system into modules may be associated with motion capability.
The highly integrated anterior dorsal module coincides with a region with
motion constraints to avoid compromising ventilation, while for the
posterior dorsal region motion constraints avoid exceeding extension of
the posterior back. On the other hand, the weakly integrated diaphragmatic
vertebra belongs to the ‘Diaphragmatic joint complex’ –a key region of the
mammalian column of exceedingly permissive motion. Our results also
demonstrate that these modules do not match with the traditional
morphological regions, and we propose natural selection as the main factor
shaping this pattern in order to stabilize some regions and to allow
coordinate movements in others.