Meeting Abstract
Archosaurs (birds, crocodylians, and their extinct relatives) evolved a wide diversity of hind limb skeletal morphologies, suggesting highly divergent articular soft tissue anatomies. However, the general lack of understanding on the dynamic interaction of archosaur joint soft tissues has hampered further functional and evolutionary inferences. Here we use contrast-enhanced computed tomography to generate 3D surface models of the pelves, femora, and joint soft tissues of the American alligator, an extant archosaur. The hip joints were then animated using marker-based XROMM to visualize soft tissue articulation and hip kinematics during forward terrestrial locomotion. The anatomical femoral head of the alligator travels beyond the cranial extent of the bony acetabulum and does not act as a central pivot as has been suggested for some extinct archosaurs. Moreover, the apex of the hyaline cartilage core interpenetrates with the ventral surface of the acetabular labrum during load-bearing phases of the high-walk, suggesting deformation of the labrum in response to compressive loads. Finally, the fibrocartilaginous surfaces of the alligator’s antitrochanter and femoral neck remain engaged during hip flexion and extension, similar to the articulation between homologous structures in birds. Our results illustrate the utility of XROMM for studying joint kinematics in light of articular soft tissue interactions. These results also allow us to propose functional hypotheses for crocodylian hip joint soft tissues, which expand our knowledge in vertebrate connective tissue biology, loading mechanics, and the role of joint soft tissues in locomotor behavior.
