Elucidating Turtle Origins with PPC-SRμCT

The turtle shell is a morphological innovation that allowed turtles to persist for more than 200 million years up to the present day. The turtle shell is not merely an external armour but an integral part of the skeleton, incorporating the vertebrae and ribs of the trunk in addition to parts of the shoulder girdle. Now, detailed morphological imaging of recently discovered fossils of Triassic stem-turtles has the potential to reconstruct how the turtle got its shell and other crucial anatomical characteristics. We propose to use propagation phase-contrast synchrotron microtomography (PPC-SRμCT) to study the anatomy of the “shell-less” stem-turtle Pappochelys and the oldest and best known fully shelled stem-turtle, Proganochelys. With these data, we will reconstuct how the closed turtle skull evolved from an “ancestral” reptilian condition, and how the turtle shell evolved by studying the anatomy and function of the thickened dorsal ribs and the rest of the Pappochelys skeleton.