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Pleurokinesis or no pleurokinesis, that is the question...

Somehow nobody seems to post SVP meeting abstracts this year. I don't know why -- there are plenty of interesting ones. Like this one:


Robin Cuthbertson (p. 64A): Pleurokinesis revisited, kinetic limitations of cranial joints in hadrosaurine dinosaurs

Pleurokinesis, a complex cranial kinetic model, has been proposed for all ornithopod dinosaurs. In hadrosaurids, this hypothesized chewing mechanism includes vertical adduction of the mandible with lateral displacement of the maxilla in combination with posterolateral movement of the quadrate. These primary actions drive a series of linked secondary motions (described below). However, based on the kinematic limitations imposed by joint structure, this collective series of motions cannot be recreated in *Brachylophosaurus canadensis* or *Edmontosaurus regalis*. Lateral movement of the maxilla is prevented by the structure of the joint between the anterior maxillary process and the premaxilla, and the articulation of the stationary lacrimal with the dorsolateral surface of the maxilla. Posterolateral rotation of the quadrate is also doubtful because this element forms a broad contact with the pterygoid, which in turn is rigidly linked to the palatine. Additional kinematic limitations render most of the imposed secondary movements unlikely. A scarf joint between the postorbital and the jugal effectively prevents translocation, and there is no evidence that the quadratojugal was capable of disarticulating from the quadrate. The proposed cylindrical movement between the pterygoid process of the basisphenoid and the pterygoid seems possible if this joint is considered in isolation, but, as noted above, the movement of the pterygoid is limited by its articulation with the palatine and quadrate. Movements that seem most likely are associated with the mandible, but they are not motions hypothesized by the pleurokinetic model. The structure of the mandibular glenoid, in particular the relatively broad and shallow articular surface of the surangular, appears capable of accommodating minimal translational movements, as well as rotation of the mandible about the quadrate condyle. Accordingly, a simplified model based on a rigid maxilla and lower jaw exhibiting limited freedom at its mandibular glenoid cannot be rejected. Further comparison of cranial joint morphology is required to establish whether a simplified chewing mechanism was present in the remaining hadrosaur taxa.