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

[David Marjanovic <david.marjanovic@gmx.at>]

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

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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.