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Hadrosaur chewing: Brachylophosaurus and Edmontosaurus lacked pleurokinesis

From: Ben Creisler

A new online paper:

Cuthbertson, R. S., Tirabasso, A., Rybczynski, N. and Holmes, R. B. (2012)
Kinetic Limitations of Intracranial Joints in Brachylophosaurus
canadensis and Edmontosaurus regalis (Dinosauria: Hadrosauridae), and
Their Implications for the Chewing Mechanics of Hadrosaurids.
The Anatomical Record (advance online publication)
doi: 10.1002/ar.22458

The highly specialized tooth morphology and arrangement of the dental
battery of hadrosaurids has led to much speculation surrounding the
chewing mechanics of this successful group of herbivorous dinosaurs.
Pleurokinesis, a long established hypothesis explaining the ornithopod
chewing mechanism, proposes a transverse power stroke in hadrosaurids
that was accommodated by vertical adduction of the mandible, lateral
rotation of the maxilla at the maxilla-premaxilla joint, lateral
rotation of the jugal-maxilla complex at its contact with the
lacrimal, and posterolateral rotation of the quadrate at its contact
with the squamosal. A secondary series of movements were also thought
to have occurred as a consequence of these primary movements. In this
article, the intracranial joint morphology is described for both
Brachylophosaurus canadensis and Edmontosaurus regalis and their
permissive kinematics are established. Based on this evidence, the
movements associated with pleurokinesis are not accommodated in these
hadrosaurine dinosaurs. Rather, the movements that seem most likely to
have produced the observed dental wear patterns are those associated
with the mandible about the jaw joint. The structure of this joint
appears well-suited to have accommodated some translation as well as
rotation of the mandible about the quadrate condyle. Three-dimensional
modeling of the alternate mandibular movements reveals that not all
the combined labiolingual width of the lingual and buccal facets of
the tooth row was involved in the power stroke. Rather, limits on the
degree of mandibular long axis rotation suggest that only the lingual
facet and the more medial portion of the buccal facet were utilized.