The adaptive significance of vertebral form in the pelvic regions of Mabuya capensis and Acontias plumbeus (Reptilia: Scincidae)

Abstract

Vertebral form in the pelvic regions of the terrestrial Mabuya capensis and the subterrestrial Acontias plumbeus reflect characteristics related to a combination of flexibility and strength. In M. capensis both the pre-and postsacral vertebrae become relatively shorter and broader towards the sacrum. This not only results in greater flexibility of the pelvic region but also provides a large bone area over which the forces generated during locomotion can be distributed. In A. plumbeus the precaudal and caudal vertebrae become relatively shorter and broader towards the precaudal-caudal transition giving its pelvic region attributes similar to that of M. capensis. The articular surfaces of the zygapophyses in A. plumbeus are larger and stretch further laterally than those of M. capensis probably allowing its vertebrae a greater degree of lateral movement. The condyles and therefore also the cotyles of A. plumbeus are broader and shorter (shallower) than those of M. capensis allowing the compressive forces generated during locomotion to be distributed over a larger bone area while also allowing the vertebrae more freedom of lateral movement. In both skinks the vertebrae have procoelous centra.