Meeting Abstract

P1-76   -   Regionalization in the lizard axial column Stefanic, CM*; Jones, KE; Turner, AH; Stony Brook University; The University of Manchester; Stony Brook University candice.stefanic@stonybrook.edu

The vertebrate axial column often has discernable regions, but recent studies reveal cryptic regions in mammals and sauropsids. Morphological changes in limb and girdle muscles with axial insertions may drive the evolution of regionalization, which in turn may facilitate specialization in locomotor capabilities. Regionalization, however, has only been studied in-depth in mammals. Our study uses patterns of presacral vertebral regionalization to explore the link between vertebral morphology and ecology in lizards, another diverse amniote clade. Lizards have a wide range of body sizes (0.2 g Brookesia nana, 100+ kg Varanus komodoensis) and ecologies (arboreal, terrestrial, aquatic). We performed segmented regression analyses on 3D vertebral shape data to uncover axial column region boundaries. Results show that presacral vertebrae across all examined species fit a four-region model, supporting the hypothesis that lizard presacral vertebrae group into finer categories than the long-accepted two-region model of a cervical and dorsal region. The anteriormost region boundary detected was between the fifth and sixth vertebrae and the posteriormost region included the last two or three presacrals. The marine iguana, Amblyrhynchus, stood out with the boundary between its anteriormost two regions falling between the sixth and seventh vertebrae and with five vertebrae comprising its posteriormost presacral region. We hypothesize that Amblyrhynchus has relatively more posterior dorsal vertebrae because, as a fully aquatic animal, it uses lateral bending of its posterior trunk and pelvis to propel itself during swimming. Extra anterior cervical vertebrae in Amblyrhynchus could relate to neck musculature associated with its unique underwater algae feeding. Our results suggest that although the number of presacral regions in lizards is conserved, the relative length of each region has implications for ecology and locomotion.