Geometric morphometric analysis of tibial shape and presentation among Catarrhine taxa

The proximal component of the talo-crural joint, the tibia, was compared, using geometric morphometrics, in 240 specimens from 10 extant taxa to identify differences in shape and the factors influencing them. The specimens were laser scanned, digitally reconstructed, and landmarked. Regression analysis was used to evaluate tibial shape, and significant amounts of shape variation among taxa were due to body mass, tibial size, superfamily, and substrate preference in the whole tibia, as well as, separate analysis of the distal tibial articular facets, and the medial malleolar facet. The most important factor for whole tibial shape was tibial robusticity, which closely correlated with body mass. However, substrate preference was also a significant factor in tibial shape and independent from body mass. Substrate preference was also the most important factor defining distal articular morphology. Principal components analysis and pairwise permutation tests were used to compare differences in morphology among taxa. Nearly all were significantly different in overall tibial shape, and distal morphology. Shape and presentational morphology associated with body mass, tibial size, superfamily, and substrate preference were identified, along with the similarities and differences among individual taxa. These were visualized by TPS deformation of an exemplar surface. Relationships among these factors were assessed with their dot-product. Results demonstrated that size significantly influenced proximal presentation, while substrate preference influenced articular morphology.