Meeting Abstract
Novel structures have been found to convey strong functional consequences in a variety of taxa. We examined the functional significance of the fusion of the pelvis to the plastron (the ventral portion of the shell), a feature unique to pleurodiran turtles. Pleurodires are one of the two extant groups of turtles, and while Cryptodires (the other extant taxa) have invaded a variety of terrestrial and aquatic habitats, nearly all pleurodire species are highly aquatic. As with all aquatic animals, they are thus subject to a myriad of potentially destabilizing forces while swimming, resulting in both rotational (pitch and yaw) and translational (heave and sideslip) movements. These motions can decrease locomotor performance, making their minimization advantageous. We hypothesized that pelvic-plastral fusion in pleurodires might improve lateral stability by reducing potential movements of the girdle relative to the shell. We used high-speed video to compare hydrodynamic stability during swimming between a pleurodiran turtle (Emydura subglobosa) and previously collected data from a cryptodiran species (Chrysemys picta) which lacks pelvic-plastral fusion. Data were collected at similar size-normalized speeds. We found that, as predicted, extraneous lateral movements (slideslip and yaw) are reduced in pleurodires. Moreover, while pleurodires and cryptodires experience similar pitch, pleurodires exhibit lower heave. We also observed E. subglobosa perform a novel gait among turtles, in which it would periodically use synchronous extension of both fore and hind limbs, producing movements that resemble an underwater ‘gallop’. Our data indicate that pleurodiran swimming may differ from that of cryptodires in a variety of parameters, which may relate to the novel pelvic construction of this group.
