Meeting Abstract
Among the two extant lineages of turtles, pleurodires show derived specializations of the pelvic skeleton that are correlated with novel originations of several hind limb muscles. Despite such novelties, pleurodires exhibit locomotor kinematics during both swimming and walking that are broadly similar to those of many generalized cryptodires. Because the function of individual muscles can depend strongly on their locations of origin, it is possible that the functional roles of some muscles may differ between pleurodires and cryptodires, even during the performance of the same behavior. To test this possibility, we measured hind limb muscle activity (EMGs) and kinematics of the aquatic generalist pleurodire Emydura subglobosa while walking and swimming, and compared these data with previous results from a generalized aquatic cryptodire, Trachemys scripta. We found that some hip muscles with differing attachments showed different activity patterns between taxa. For example, puboischiofemoralis internus (PIFI) protracts the hip during swing in walking cryptodires, but also shows a novel low-amplitude burst during stance in E. subglobosa. Because the origin of PIFI has shifted ventrally to the shell in pleurodires, this additional burst could aid limb adduction or stabilization. However, activity patterns also differ between the taxa for some muscles in which attachments are similar: for example, the knee extensor femorotibialis shows a later burst in E. subglobosa than in T. scripta, corresponding with delayed knee extension. Our results suggest that, in turtles, novel neuromotor patterns can be correlated with differences in muscular arrangement, but also between muscles that retain similar attachments.
