Conserved patterns and locomotor-related evolutionary constraints in the hominoid vertebral column

The evolution of the hominoid lineage is characterized by pervasive homoplasy, notably in regions such as the vertebral column, which plays a central role in body support and locomotion. Few isolated and fewer associated vertebrae are known for most fossil hominoid taxa, but identified specimens indicate potentially high levels of convergence in terms of both form and number. Homoplasy thus complicates attempts to identify the anatomy of the last common ancestor of hominins and other taxa and stymies reconstructions of evolutionary scenarios. One way to clarify the role of homoplasy is by investigating constraints via phenotypic integration, which assesses covariation among traits, shapes evolutionary pathways, and itself evolves in response to selection. We assessed phenotypic integration and evolvability across the subaxial (cervical, thoracic, lumbar, sacral) vertebral column of macaques (n = 96), gibbons (n = 77), chimpanzees (n = 92), and modern humans (n = 151). We found a mid-cervical cluster that may have shifted cranially in hominoids, a persistent thoracic cluster that is most marked in chimpanzees, and an expanded lumbosacral cluster in hominoids that is most expanded in gibbons. Our results highlight the highly conserved nature of the vertebral column. Taxa appear to exploit existing patterns of integration and ontogenetic processes to shift, expand, or reduce cluster boundaries. Gibbons appear to be the most highly derived taxon in our sample, possibly in response to their highly specialized locomotion.

Methods
This dataset includes linear data from the subaxial vertebral column (cervical, thoracic, lumbar, and sacral) of 96 Macaca mulatta, 76 Hylobates lar, 92 Pan troglodytes, and 29 Homo sapiens individuals. 

Data were collected using a Mitutoyo Digital Caliper accurate to 0.02 mm and are reported in millimeters (mm). "." is used to denote a decimal throughout. Raw linear data are provided for all available elements for each individual. Missing data is noted with 'NA' and indicates the element or trait was missing. Intraobserver error ranges between 1.06-1.28%. 

Not all individuals display the modal formula for that taxon. Vertebral IDs have been adjusted as described in the associated manuscript and README file.

Human data from the British Museum are anonymized.