The Caudofemoralis Longus Muscle and Musculoskeletal Plasticity in the American Alligator

Event Center A&B

The caudofemoralis longus muscle (CFL) - a major retractor and medial thigh rotator- is welldeveloped in reptiles with a sprawling gait and a long tail. The CFL originates on the transverse processes and chevrons of the caudal vertebrae and inserts on the fourth trochanter of the femur. Evolutionary changes to hindlimb orientation and tail morphology among theropod dinosaurs have been ascribed to a reduced role of the CFL in terrestrial locomotion, but no experimental alteration of CFL function has been attempted. To investigate the interplay between CFL and skeleton, we used bilateral tenotomy to deactivate the CFL in juvenile (n=12) American alligators (Alligator mississippiensis). After eight months, experimental CFL wet mass and fiber length were significantly reduced by 23% and 13% respectively, compared to controls. Femur length, and external diameter and position of the fourth trochanter were similar between groups. Femur cross sections taken at the fourth trochanter revealed that cross sectional area, and polar movement of inertia were also similar between groups. CFL tenotomy thus elicited changes in terrestrial locomotor performance were observed following tenotomy, our results suggest that voluntary locomotor patterns in crocodilians are dictated primarily by skeletal morphology rather than muscle morphology. Further monitoring of bone growth/remodeling following tenotomy will allow us to investigate the CFL-driven phenotypic plasticity of the archosaur locomotor system and elucidate the role musculoskeletal strain in shaping the evolutionary transformation of the hindlimb/tail module in archosaurs.