A Review and Evaluation of the Scientific Literature on the Early Evolution of Turtles

Abstract

Turtles are unique organisms within the animal kingdom. Unlike any other living reptile, their skulls have neither an upper nor lower opening in the temporal region. All other living reptiles and birds are diapsid, possessing both temporal openings on each side of the skull. For the turtle shell to form, primitive turtles must have experienced several changes, including the rib cage surrounding the shoulder blades and the flattening and extending of the ribs. Because of these unique features, it has been difficult to place turtles into a taxonomic group, a debate that has been going on since Reptilia was first named in 1768. Despite the great amount of study on living and fossil turtles, there are many controversies remaining on their origins and on how they developed their unique features. Each new fossil discovery and idea proposed requires one to look back with a new perspective and reinterpret old literature. The purpose of this thesis is to review and summarize current and past research regarding the origin and early evolution of turtles, as well as their relationship with other animal groups. In this study I am also analyzing the information collected in order to determine the most likely hypotheses regarding these topics.