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Osteological redescription of the skull of Microcleidus homalospondylus (Sauropterygia, Plesiosauria) from the Lower Jurassic of England

Published online by Cambridge University Press:  14 July 2015

David Brown ,
Peggy Vincent  and
Nathalie Bardet
David Brown
Affiliation:
School of Dental Sciences, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4BW, UK,
Peggy Vincent
Affiliation:
CR2P-UMR 7207 CNRS, Muséum National d'Histoire Naturelle, Univ. Paris 06, 57 rue Cuvier, CP38, F-75005, Paris, France, ; Staatliches Museum für Naturkunde, Rosenstein 1, D-70191 Stuttgart, Germany
Nathalie Bardet
Affiliation:
CR2P-UMR 7207 CNRS, Muséum National d'Histoire Naturelle, Univ. Paris 06, 57 rue Cuvier, CP38, F-75005, Paris, France, ;
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Abstract

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.

Type
Research Article
Information
Journal of Paleontology , Volume 87 , Issue 4 , July 2013 , pp. 537 - 549
Copyright
Copyright © The Paleontological Society 

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