Movements of the pelvic girdle facilitate terrestrial locomotor performance in a wide range of vertebrates by increasing hind limb excursion and stride length. The extent to which pelvic movements contribute to limb excursion in turtles is unclear because the bony shell surrounding the body presents a major obstacle to their visualization. In the Cryptodira, which are one of the two major lineages of turtles, pelvic anatomy indicates the potential for rotation inside the shell. However, in the Pleurodira, the other major suborder, the pelvis shows a derived fusion to the shell, preventing pelvic motion. In addition, most turtles use their hind limbs for propulsion during swimming as well as walking, and the different locomotor demands between water and land could lead to differences in the contributions of pelvic rotation to limb excursion in each habitat. To test these possibilities, we used X-ray reconstruction of moving morphology (XROMM) to compare pelvic mobility and femoral motion during walking and swimming between representative species of cryptodire (Pseudemys concinna) and pleurodire (Emydura subglobosa) turtles. We found that the pelvis yawed substantially in cryptodires during walking and, to a lesser extent, during swimming. These movements contributed to greater femoral protraction during both walking and swimming in cryptodires when compared with pleurodires. Although factors related to the origin of pelvic-shell fusion in pleurodires are debated, its implications for their locomotor function may contribute to the restriction of this group to primarily aquatic habits.
The authors declare no competing or financial interests.
C.J.M. and R.W.B. conceived the study and performed surgical procedures; C.J.M., E.L.B. and R.W.B. collected data; C.J.M. and E.L.B. analyzed data. All authors contributed to manuscript preparation and approved the manuscript.
This work was supported by a travel grant from The Company of Biologists to C.J.M.; Clemson University creative inquiry funds [grant no. 479 to R.W.B.]; and the National Science Foundation [1262156 to E.L.B.].
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.141622.supplemental
- Received April 7, 2016.
- Accepted June 15, 2016.
- © 2016. Published by The Company of Biologists Ltd