Meeting Abstract
Mammalian cervical vertebrae enable a variety of critical functions, including supporting the head, allowing flexion, extension, and rotation of the neck, influencing posture and locomotor behavior, housing the spinal cord, and anchoring axial muscles. The atlas (C1) in particular has a distinct functional role and exhibits pronounced variation among species. However, functional morphology of the cervical vertebrae has not been widely studied, and previous quantitative work on atlas shape in relation to ecology is focused only on haplorrhine primates. To investigate how atlas shape is influenced by the functional demands of supporting the head and flexing and extending the neck, we used 3D geometric morphometrics to quantify the shape of the atlas in 64 species of Euarchontogliran mammals. Our ecologically and taxonomically diverse sample includes primates, rodents, lagomorphs, tree shrews, and colugos. Data on body size, relative head size, posture, and locomotion were gathered from the literature and analyzed in relation to 3D atlas shape using phylogenetic generalized least squares (PGLS) regression. The first principal component axis of shape describes variation in the anterior-posterior length of the vertebra, while the second axis describes variation in the dorsal-ventral height and the convexity of the edge of the transverse process. When phylogeny was taken into account, shape variation along both PCs was not correlated with any size or behavioral variables. Our findings indicate that atlas vertebra shape may be influenced by phylogenetically inherited constraints at broad taxonomic scales in mammals.
