Meeting Abstract

P1.109  Thursday, Jan. 3  Skeletal Kinematics of Upper Bill Movement During Feeding in Mallard Ducks, Anas platyrhynchos DAWSON, M.M.*; METZGER, K.A.; BAIER, D.B.; BRAINERD, E.L.; Brown University megan_dawson@brown.edu

Cranial kinesis in extant birds involves movement of the upper bill (maxilla) relative to the braincase at the craniofacial hinge. Here we use CTX, a new visualization technique that combines two x-ray fluoroscopic views with a static CT scan, to visualize cranial kinesis in Mallard Ducks during feeding. The braincase, maxilla, quadrate, mandible and jugal were surgically marked with tantalum beads, allowing us to reconstruct the movement of these bones in animation software. The duck craniofacial hinge consists of a pair of synovial joints between the maxilla and frontal bones, with two thin laminae of bone crossing the joint medially. During feeding, the maxilla rotates upward with respect to the braincase, by as much as 15�. The anatomy of the craniofacial hinge, combined with the movement we observed at this joint, suggest that the thin laminae in the center of this joint are bending with every cycle of maxillary elevation. How this is possible without fatigue failure remains to be determined by histological and mechanical characterization of this tissue. Previous studies based on manipulations of models and post-mortem specimens have suggested that the maxilla is raised by transferring force from rotation of the quadrate through the jugal bar and the pterygoid-palatine complex. Our reconstruction allows us to describe the translation and rotation of the quadrate, which previously has not been done in vivo. Preliminary results show quadrate rotation in phase with maxillary elevation, in support of the proposed model. We also expect that our CTX data will allow us to determine whether upper jaw and lower jaw movement are coupled.