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Plotosaurus (Mosasauridae) cranial kinesis loss



From: Ben Creisler
bcreisler@gmail.com

In the new JVP:


Aaron R. H. LeBlanc, Michael W. Caldwell & Johan Lindgren (2013)
Aquatic adaptation, cranial kinesis, and the skull of the mosasaurine
mosasaur Plotosaurus bennisoni.
Journal of Vertebrate Paleontology 33(2): 349-362
DOI:10.1080/02724634.2013.726675
http://www.tandfonline.com/doi/full/10.1080/02724634.2013.726675



New anatomical observations of the holotype skull of Plotosaurus
bennisoni from the Maastrichtian Moreno Formation of California,
U.S.A., are used as a framework to examine cranial kinesis in derived
members of the Mosasaurinae. Enlarged posteromedial flanges of the
frontal and extensive lateral contacts of the prefrontal and
postorbitofrontal contributed to increased rigidity along the
frontoparietal suture (the mesokinetic joint). Sutural contacts of the
parietal with the supraoccipital posteriorly and the prootic ventrally
would have restricted metakinetic movements. Furthermore, the unusual
shape of the epipterygoid, and its dorsal contact with the prootic and
parietal, shows that the epipterygoid and pterygoid were probably not
capable of anteroposterior movements. Most strikingly, Plotosaurus
exhibits a tight association of the quadrate with the temporal arcade,
suggesting that streptostyly was limited or lost in this derived
mosasaurine, the loss of such a feature having never been described in
a mosasaur. These charcteristics are placed in a functional context to
examine aquatic adaptations in mosasaurs. As one of the most
specialized mosasaurs known, the loss of cranial kinesis may have
evolved as a result of its piscivorous diet.