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Microcleidus (Plesiosauria) skull redescribed



From: Ben Creisler
bcreisler@gmail.com

In the new issue Journal of Paleontology:

David Brown, Peggy Vincent  and Nathalie Bardet (2013)
Osteological Redescription of the Skull of Microcleidus
homalospondylus (Sauropterygia, Plesiosauria) from the Lower Jurassic
of England.
Journal of Paleontology 87(4):537-549. 2013
doi: http://dx.doi.org/10.1666/11-104
http://www.bioone.org/doi/abs/10.1666/11-104


The plesiosaur specimen NHMUK 36184 from the Lower Jurassic of Whitby,
Yorkshire and kept in the Natural History Museum of London, comprises
an almost entire skeleton with nearly complete skull. It was described
as one of two syntypes of Plesiosaurus homalospondylus by Owen, and
selected as the lectotype by Lydekker. Extensive preparation of the
skull has revealed it as one of the most complete and best-preserved
Jurassic plesiosaurian skulls known, and its description adds
much-needed data to our knowledge of the cranial osteology of the
Plesiosauria. The three-dimensional preservation permits a relatively
reliable reconstruction of its form. Microcleidus homalospondylus
displays an interesting combination of cranial characters present in
Jurassic plesiosauroids and Cretaceous Elasmosauridea. Its snout
presents a very distinctive sculpture; the first pair of premaxillae
teeth are extremely reduced; the frontal is partially overlain by the
premaxillae, contacts the pineal foramen but does not contact the
temporal fenestra; the jugal does not contact the orbit nor the
temporal fenestra; the squamosal contacts the postorbital but not the
maxilla and presents a bulb; the postfrontal contacts the
posterolateral orbit margin; the anterior interpterygoid vacuity is
absent; the pterygoids meet posterior to the posterior interpterygoid
vacuities and are pierced by a foramen at this level; the quadrate
ramus of the pterygoid presents a ventromedial flange; the
parasphenoid is crested; the epipterygoid contacts the parietal; the
paroccipital process is spatulate distally; the prootic presents an
anteroventral process; the mandibular symphysis is keeled and bears
four pairs of teeth. Microcleidus appears very similar to Hydrorion
and Occitanosaurus, and the three taxa share a great number of
plesiomorphic characters with basal plesiosaurians and pliosauroids.