DOI: 10.5061/dryad.3j9kd51ft
title: Serial disparity in the carnivoran backbone unveil a complex adaptive role in metameric evolution

description: Multi-element systems such as the vertebral column of vertebrates
 represent a major challenge to phenotypic quantification and
 macroevolutionary analyses. The vertebral column is a metameric structure,
 composed of serially repeated subunits, and much of what is known so far
 has been inferred from sparse anatomical samples, providing little insight
 into local-scale (i.e. vertebra-to-vertebra) variation and its
 macroevolutionary importance. This limits understanding of how
 evolutionary constraints and functional adaptation interact during the
 evolution of multi-element phenotypes. Here, we quantify morphological
 disparity across all subunits (vertebrae) of the pre-sacral column in the
 mammalian order Carnivora. We address how vertebral morphology varies
 among elements, and the extent to which these patterns have been
 structured by constraints and/or evolutionary adaptation to locomotory
 capabilities, using 3D geometric morphometrics and multivariate analyses
 for high-dimensional phenotypes. We find that lumbars and posterior
 thoracics exhibit high individual disparity but low serial
 differentiation. These vertebrae are pervasively recruited into locomotory
 functions, exhibiting high-dimensional ecomorphological signals and
 patterns of evolution indicative of relaxed constraints. Cervical and
 anterior thoracic vertebrae have low individual disparity and greater
 serial differentiation. Individual vertebrae in these regions unexpectedly
 also show signals of locomotory adaptation that were not generally
 recognized by previous studies. These are characterized by low-dimensional
 ecomorphological signals and overall constrained patterns of evolution.
 Our findings support the hypothesis that the lumbar region is a key
 innovation that increases ecological versatility of mammalian locomotion.
 Nevertheless, locomotory adaptation is more widely distributed along the
 mammalian axial skeleton. This has been masked by local-scale variation
 and low phenotypic variability in comparison with other skeletal
 structures such as the skull or limbs. Our analyses demonstrate that the
 strength of ecomorphological signal does not have a predictable influence
 on macroevolutionary outcomes even within the same structure, and
 undermine the traditional view that highly constrained skeletal units are
 strongly limited in their potential to adapt to new ecological avenues.
 Our findings emphasize the importance of quantifying local-scale variation
 in functionally versatile, multi-element phenotypes such as the vertebral
 column, or indeed, the vertebrate skeleton as a whole.
description: All presacral vertebraewere
 scanned in 3D with either micro-computed tomography (CT) scanning or a
 NextEngine® surface scanner. CT scans were segmented in Avizo. This
 resulted in 3D models of 1097 vertebrae. The 3D models were imported into
 Meshlab (Cignoni et al. 2008) to reduce the size of the models. In
 addition, we used the software Netfabb to edit the 3D models and to
 separate each vertebrae of a given vertebral column. To capture the morphology of the
 vertebrae, we digitized 34 homologous landmarks on the cervical vertebrae
 (C03-C07), 32 homologous landmarks on the thoracic vertebrae (T01-T14),
 and 36 homologous landmarks on the lumbar vertebrae (L1-L7) (see Fig. 2;
 Table S2). The landmarks were digitized with the software
 <i>Landmark</i> from IDAV (Wiley et al. 2005) and the
 <i>x,y,z</i> coordinates of each landmark were exported as a
 Text file. Raw
 landmark data were imported into the R package <i>geomorph</i>
 version 3.1.0 (Adams et al. 2019). Each region of the vertebral column
 (cervical, thoracic, and lumbar) was separated into different datasets,
 and therefore, all subsequent analyses were performed
 independently.