Meeting Abstract

P3.201  Sunday, Jan. 6  Anatomy of archosaur hip joint soft tissues and its significance for interpreting hindlimb function TSAI, H.T.*; HOLLIDAY, C.M.; Univ. of Missouri, Columbia; Univ. of Missouri, Columbia hptkr7@mail.missouri.edu

Reconstructing the appendicular joint anatomy of archosaurs is critical for understanding their posture, locomotor behavior, ecology, and evolution. Soft tissue significantly contributes to the shape and size of archosaur joints, such that fossil archosaurs often exhibit incongruent bony articular surfaces. This study infers the amount of soft tissue once present in archosaur hip joints via congruence tests, as well as investigates the hip joint cartilage anatomy of archosaurs. Differences in the mediolateral depth, as well as dorsoventral and craniocaudal diameters of the femoral head and the acetabulum are used to test for congruence of the hip joint in each axis. Hip joints of suchians and basal dinosaurs (i.e. Shuvosaurus and Coelophysis) are more congruent along the craniocaudal axis than those of derived non-avian dinosaurs (i.e. hadrosaurids, sauropods, tetanurans). Furthermore, non-avian dinosaurs exhibit mediolaterally longer femoral articular surface than the depth of the acetabulum, whereas basal suchians exhibit mediolaterally wider acetabulum than the femoral articular surface. Dissections and histology of extant archosaur hip joints show that articular cartilage exhibits localized morphological differences associated with assumed loading regimes. These results indicate that an increased amount of femoral articular cartilage is associated with the medial rotation of the proximal femur during non-avian dinosaur evolution, which impact our hypotheses of femoral regional homology and hip joint function.