Meeting Abstract
Although primarily composed of the ribs and novel dermal bones, the turtle carapace (the dorsal portion of the turtle shell) also incorporates elements of the vertebral column. The vertebral column in turtles does not play the same locomotor roles as it does in other species, but there is nonetheless extensive variation in vertebral morphology among turtles. In some species, such as the matamata (Chelus fimbriatus) the vertebral column is well-developed, with expanded transverse processes and a large cross-sectional area. In other species, the vertebral column is relatively much smaller. We asked whether the vertebrae might function to increase the strength of the carapace, such that modifications in vertebral structure could be linked to changes in functional performance (even though the variation in vertebral structure might not be driven by selection for mechanical performance). We used CT slices to construct two finite element (FE) models of the same Kinosternon subrubrum (Eastern mud turtle) specimen – one with a vertebral column, and one without. The models were scaled to the same surface area (the specimen without the vertebral column was originally slightly smaller) and then each was subjected to a series of 200N loads on the carapace. For each load, both stress (von Mises stresses) and deformation were compared between models. The model without a vertebral column did indeed develop higher stresses for nearly all loads, although the difference in stress never exceeded 12%. Similarly, the two models showed slightly different patterns of deformation, particularly for loads directly over the vertebral column. The turtle vertebral column does contribute to the strength of the shell, raising the possibility of future studies investigating the effects of expanding different parts of the vertebrae for enhancing mechanical performance.
