Kinematics of the quadrate bone during feeding in mallard ducks
Published abstract (PDF,65KB).
The avian quadrate is complex in both its shape and kinematics, making it a difficult bone to describe and understand functionally. Because the quadrate plays a central role in feeding mechanics, particularly in the elevation of the upper bill, understanding its kinematics and interaction with other bones is important for more general analysis of feeding function. It has been hypothesized that the movement of the quadrate is transferred primarily through the pterygoid and palatine bones to the upper bill. Despite being key to upper bill movement, previous studies have not been able to adequately describe the movements of the quadrate. It has been suggested that the quadrate swings anteriorly and medially about its articulation with the braincase during upper bill elevation, but has not been demonstrated in vivo. Here, we use X-ray Reconstruction of Moving Morphology (XROMM) to study the movements of the quadrate and their effects on articulating bones during filter feeding in mallard ducks, Anas platyrhynchos. Rather than swinging in a single plane, the quadrate rotates about several axes during a bill elevation cycle. To describe this complex motion, we use a combination of axes defined by anatomical landmarks and helical axes. We found, as expected, that quadrate movement correlates with upper bill elevation. During upper bill elevation, the quadrate rotates anteriorly at the quadrate-braincase joint about a mediolateral axis and medially about a rostrocaudal axis. These rotations act to produce anterior and medial movement of the articulation between the quadrate and pterygoid. In addition, the quadrate rotates clockwise (viewed from above) about a dorsoventral axis during upper bill elevation, contributing to the medial and anterior movement.
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