Meeting Abstract
Both modern birds and crocodilians have derived respiratory systems with divergent morphologies. This is coupled with divergent modifications to the ribcage, and differences in the mechanics of ventilation between these two groups. However, understanding the co-evolution of ribcage morphology and ventilation mechanics in living archosaurs has been hindered by a lack of integration between kinematic and anatomical data, which in turn creates difficulties in reconstructing motion in fossils. Here, we employ a joint-based approach to represent both bone morphology and motion. In vivo rib kinematics were recorded during ventilation in living crocodilians and birds using XROMM (X-ray reconstruction of moving morphology), with motion measured relative to the articular surfaces of the costovertebral joint; axes of rib translation and rotation were defined with respect to specific homologous landmarks on the ribs and vertebrae. This approach then served as the basis for “scientific motion transfer”, applying motion patterns observed in modern archosaurs to their fossil relatives- specifically, non-avian dinosaurs- in a framework grounded in the anatomy of the costovertebral joint. This new approach provides a testable and repeatable way of predicting ventilation kinematics in extinct taxa. Morphometric analysis of archosaur vertebral morphology suggest that dinosaurs had costovertebral joints most similar to modern birds, and may have employed bird-like rib kinematics. However, the initial XROMM results also show that bony morphology alone is not a good predictor of rib motion, and greater consideration should be given to the soft-tissue anatomy of the costovertebral joint.
