Meeting Abstract
Mammalian locomotion relies on bending in the dorsoventral plane to achieve asymmetric gaits, which increase speed and facilitate respiratory-locomotor coupling. This is in contrast to other amniote groups (i.e., lepidosaurs) which emphasize lateral bending during locomotion. To enable this behavior, the mammalian trunk is highly specialized. In particular, the anatomy of the ribless lumbar region promotes dorsoventral mobility, and thus is central to the evolution of fast gaits in mammals. To understand the link between vertebral anatomy and mammalian locomotion, we quantitatively examined vertebral variation across a broad sample of mammals, and compared it to that of lepidosaurs and archosaurs. We compared vertebral anatomy among synapsids and diapsids using 3D geometric morphometrics (n=48, 250 vertebrae). Sixty-four landmarks were taken, including 44 fixed and 20 sliding semilandmarks, at five vertebral positions. Variation was examined using Principal Components Analysis, within extant groups and across the amniote clade. The influence of vertebral position, body size and phylogenetic relationships was examined. Comparisons of extant taxa (36 mammals, 12 diapsids) revealed significant variation based on vertebral position and locomotor mode. Mammals had the greatest intracolumn variation, due to their extreme dorsal regionalization. Variation between taxa is greatest in the lumbar region, while thoracic vertebrae tends to sort phylogenetically. Implications for mammal evolution are discussed.
