Libonectes (Plesiosauria) skull and jaw muscles

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

New in Palaeontologia Electronica:

Ricardo Araújo and Michael J. Polcyn (2013)
A biomechanical analysis of the skull and adductor chamber muscles in
the Late Cretaceous Plesiosaur Libonectes.
Palaeontologia Electronica  16(2): 10A: 25p
http://palaeo-electronica.org/content/2013/418-plesiosaur-mastication


Plesiosaurs were a diverse clade of marine reptiles that spanned
nearly three-quarters of the Mesozoic (earliest Jurassic to latest
Cretaceous). They exhibit variation in head and neck morphology that
presumably relates to functional differences in feeding habits.
However, from a biomechanical standpoint, these marine creatures have
a cranial organization shared with few reptile clades: the neodiapsid
condition. Nevertheless, basic structural features in some derived
clades, such as elasmosaurids, remain poorly understood, namely the
presence of large supratemporal fenestrae, tall temporal bars, and
high parietal crests. These features present biomechanical compromises
with paleobiological implications for feeding habits. Here we test
specific hypotheses regarding skull structure and mechanics in the
elasmosaurid plesiosaur Libonectes morgani from the Late Cretaceous of
Texas (USA). Using finite element analysis and loadings based on a
detailed reconstruction of adductor chamber musculature, we provide
estimates of stress and strain distributions for the Libonectes skull.
We also digitally morphed different anatomical variants of the
Libonectes skull, in order to assess the role of those traits in
skull's mechanical performance (e.g., height of the temporal bar). Our
results show that a larger physiological cross-section of the adductor
muscles is achieved by an enlarged supratemporal fenestra which
although it reduces mechanical performance of the skull, it is offset
by increased strength of a taller parietal crest and temporal bar,
given the loading is largely symmetrical, the lateral components are
offsetting yielding a vertical force vector. This arrangement also
increases the length of the adductor musculature and thus the total
muscle mass. We propose that the reduced pterygoid flange indicates a
diminished role for the pterygoideus muscle, reflecting a shift of the
majority of the bite force to the adductor mandibulae externus,
pseudotemporalis, and adductor mandibulae posterior muscles. Reduction
of the pterygoideus falsifies the dual adductor system hypothesis, in
which kinetic inertia and static pressure coexist.