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 might contribute to limb excursion in turtles is unclear, because the bony shell surrounding the body presents a major obstacle to their visualization. In cryptodires, one of the two major lineages of turtles, pelvic anatomy indicates the potential for rotation inside the shell. However, in pleurodires, the other major lineage of turtles, the pelvis shows a derived fusion to the shell, likely 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 subglobossa) turtles. We found that the pelvis yawed substantially in cryptodires during walking and, to a lesser extent, during swimming. These movements contributed to cryptodires having greater femoral protraction in both walking and swimming when compared to pleurodires, in which the pelvis was immobile. Though 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.
- Received April 7, 2016.
- Accepted June 15, 2016.
- © 2016. Published by The Company of Biologists Ltd