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Plioplatecarpus braincase and endosseous labyrinth

Ben Creisler

A new online paper:

Robin Cuthbertson, Hillary C. Maddin, Robert Holmes and Jason S. Anderson (2015)
The braincase and endosseous labyrinth of Plioplatecarpus peckensis
(Mosasauridae, Plioplatecarpinae), with functional implications for
locomotor behaviour.
The Anatomical Record (advance online publication)
DOI: 10.1002/ar.23180

Adaptations of mosasaurs to the aquatic realm have been extensively
studied from the perspective of modifications to the post-cranial
skeleton. In recent years, imaging techniques such as computed
tomography have permitted the acquisition of anatomical data from
previously inaccessible sources. An exquisitely preserved specimen of
the plioplatecarpine mosasaur Plioplatecarpus peckensis presents an
opportunity to examine the detailed structure of the braincase, as
well as the form of the otic capsule endocast. These data elaborate
upon previous descriptions of the braincase of Plioplatecarpus, and
provide a detailed, three dimensional reconstruction of the osseous
labyrinth for the first time. The otic capsule endocasts reveal that
the size of the labyrinth relative to head size is comparable to that
of other squamates, suggesting that labyrinth size was not a factor in
increasing sensitivity. However, all three semicircular canals are
tall and strongly arced to a degree comparable to, and even exceeding,
that observed in arboreal and aquatic lizards. Comparison of the
sensitivity of the canals in each of the three major axes of rotation
suggests Plioplatecarpus peckensis may have been most sensitive to
movements in the pitch axis. Although early mosasaurs were probably
anguilliform swimmers, most are thought to have been subcarangiform to
thunniform locomotors with a near-rigid body form and likely decreased
maneuverability. The data from the labyrinth presented here add a
potential new dimension to this model of locomotion for further
consideration, wherein changes in orientation, such as pitch, may have
been more common locomotor behaviours than previously thought.