Serial disparity in the carnivoran backbone unveils a complex adaptive role in metameric evolution

Organisms comprise multiple interacting parts, but few quantitative studies have analysed multi-element systems, limiting understanding of phenotypic evolution. We investigate how disparity of vertebral morphology varies along the axial column of mammalian carnivores - a chain of 27 subunits - and the extent to which morphological variation have been structured by evolutionary constraints and locomotory adaptation. We find that lumbars and posterior thoracics exhibit high individual disparity but low serial differentiation. They are pervasively recruited into locomotory functions and exhibit relaxed evolutionary constraint. More anterior vertebrae also show signals of locomotory adaptation, but nevertheless have low individual disparity and constrained patterns of evolution, characterised by low-dimensional shape changes. Our findings demonstrate the importance of the thoracolumbar region as an innovation enabling evolutionary versatility of mammalian locomotion. Moreover, they underscore the complexity of phenotypic macroevolution of multi-element systems and that the strength of ecomorphological signal does not have a predictable influence on macroevolutionary outcomes. Figueirido et al. use a 3D geometric morphometric approach to study functional among-species disparity in the vertebral column of Carnivora, as well as assessing the effect of different sampling methods on homology. Disparity is generally higher in more caudal regions, compared to more cranial regions, but recruitment for locomotor function is pervasive throughout the whole studied column.

Automated summary

The research found that lumbar and posterior thoracic vertebrae exhibit high individual disparity but low serial differentiation, while more anterior vertebrae show constrained patterns of evolution. The thoracolumbar region is considered as a key innovation enabling evolutionary versatility of mammalian locomotion.