Meeting Abstract

P3.72  Wednesday, Jan. 6  The evolution of turtle shell kinesis: A comparative review CORDERO, G.A.; Iowa State University gcordero@iastate.edu

Recently discovered fossil evidence from the Triassic (220 MYA) suggests that the presence of the plastron preceded that of the carapace in the oldest known ancestral form of modern turtles. Beginning in the Tertiary, the shell underwent substantial diversification as turtles left the oceans to colonize terrestrial environments. Such diversifying events likely facilitated the evolution of shell kinesis as a structural adaptation enhancing predator defense, diet, and reproduction. Specifically, kinesis allows for the complete withdrawal of limbs, the opening of the anterior carapace to accommodate larger prey items, and of the posterior in species that lay large eggs. To frame shell kinesis within a systematic context, we review all currently available descriptions of turtle species and emphasize their position on a molecular phylogenetic tree. Additionally, we map the distributions of the taxa in question to draw biogeographical inferences. Our analysis suggests that plastral kinesis has evolved independently in families Kinosternidae, Emydidae, Geoemydidae, Pelomedusidae, and Testudinidae. Moreover, distinct variations of kinesis mechanisms occur among subclades of those families. Carapacial kinesis and pankinesis are less common but have arisen independently in the Testudinidae and Trionychidae, respectively. Moreover, kinesis appears independently in turtles in North and South America, Europe, Africa, and Asia. Thus, this adaptation in an iconic trait provides an excellent model of morphological convergence in a successful, globally distributed clade.