Patellar shape diversity as a functional indicator of locomotor specialization in selected ruminant species

Abstract

This study investigates interspecific and intraspecific variation in patellar morphology among the examined species of ruminants and explores whether these differences are consistent with their reported locomotor ecology. While the patella functions as a crucial lever during locomotion, the extent to which this relatively small bone reflects adaptive variation across species remains uncertain. This research aims to characterize patellar shape diversity in five selected ruminant species and to explore its potential functional implications within this limited comparative framework. A total of 352 patellae representing five ruminant species (Bos taurus, Bison bonasus, Ovis aries, Capra hircus, and Capreolus capreolus) belonging to the families Bovidae and Cervidae were digitized as three-dimensional models and analyzed using geometric morphometrics. Morphospace distributions, shape variation, and allometric relationships were assessed. Distinct patellar morphologies were observed among the examined species. Bos taurus formed a distinct cluster, whereas European bison (Bison bonasus) largely overlapped with the sheep cluster in shape space. Nevertheless, Bovids tended to exhibit relatively more medio-lateral expansion and more developed cartilaginous processes, consistent with greater weight-bearing demands and joint stability. In contrast, Capreolus capreolus and Capra hircus displayed slender, elongated patellae with reduced projections, a morphology that may be associated with agility and speed-related locomotor demands. Ovis aries occupied an intermediate morphospace, overlapping partially with both large and small ruminants. Procrustes ANOVA confirmed significant shape differences among the examined species, excluding sheep and goats. Allometric analyses revealed a strong association between patellar shape and centroid size in this dataset of five species. These findings demonstrate that, in the studied species, patellar morphology reflects an intricate interplay of functional adaptation, phylogenetic relatedness, and allometric scaling. Despite its small size, the patella may serve as an informative morphological marker of ecological and functional differentiation among ruminant species within the comparative framework examined here, and the patterns observed in this study may help generate hypotheses for broader comparative analyses in other ruminant taxa.