The evolution of neck retraction mechanisms in basal turtles

• Applicant: Professor Dr. Walter Joyce
• Subject Area: Palaeontology
• Term: from 2011 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 184182171

Turtles are unique among vertebrates in that they possess a bony shell under which they can withdraw their heads and necks. In pleurodiran turtles, the head and neck are folded along the horizontal plane below the shell, whereas in cryptodiran turtles, the head and neck are retracted inside the shell between the shoulder girdles. Although the neck retraction mechanisms of living turtles are generally wellunderstood, virtually nothing is known about the evolution of neck mobility among fossil turtles and the origin of these mechanisms thus remains unclear. To complement what is known about the muscle system of extant turtles, I propose as the first step to sample the remaining tree space by dissecting the necks of four extant turtles. Within a phylogenetic framework, this will allow reconstructing the muscle system of the hypothetical turtle ancestor. For the second step, I propose investigating the mechanical constraints that the musculoskeletal system imposes on the necks of extant turtles, by documenting the maximum allowed flexibility of fresh turtle necks using x-ray photography. With the data obtained from the first and second step, it then will be possible to 3D model the neck movement of several well-preserved fossil taxa that will have been CT or laser scanned for that purpose and to synthesize the evolution of neck retraction mechanisms in turtles.

• DFG Programme: Research Grants