Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341402
Title: A taxonomic and functional study of the Callovian (Middle Jurassic) Pliosauroidea (Reptilia, Sauropterygia)
Author: Noe`, Leslie Francis
Awarding Body: University of Derby
Current Institution: University of Derby
Date of Award: 2001
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Abstract:
The short-snouted Callovian pliosaurs, Liopleurodon ferox SAUVAGE 1873, Simolestes vorax ANDREWS 1909 and Pachycostasaurus dawni CRUICKSHANK, MARTILL and NOE 1996, of the Peterborough Member, Oxford Clay Formation are of considerable palaeontological importance. The restricted geographical and temporal range, exceptional preservation, relative abundance, and easy removal of matrix, make the Callovian pliosaurs excellent subjects for detailed study. Skull material is known from all Callovianpliosaurs, but has been little studied, and much excellent material remains undescribed. The taxonomy of the short-snouted Callovian pliosaurs is thus in need of critical revision. Cranial functional morphology goes largely undiscussed, and the palaeoecological position of the short-snouted genera is poorly understood. The taxonomy of the short-snouted Callovian pliosaurs is critically revised, and the genera Liopleurodon, Simolestes and Pachycostasaurus shown to be monospecific and taxonomically valid. The holotype material for Liopleurodon ferox is poor (a single tooth) but exhibits sufficient characteristics for taxonomic definition. The holotype material of Simolestes vorax and Pachycostasaurus dawni, an incomplete skull and postcranial skeleton in each case, is taxonomically robust. Never before attempted cranial reconstructions, in multiple views, are presented for each genus. Detailed cranial, mandibular and dental descriptions of Liopleurodon and Simolestes are presented, with description of many new, newly recognised and previously unfigured specimens. The presence of nasals is definitively demonstrated for the first time in any pliosaur genus. The likely presence of a lacrimal in Liopleurodon indicates the relatively plesiomorphic position of the pliosaurs within the Plesiosauria. The skull ofPachycostasaurus is described for the first time, although in less detail than the other two genera due to relatively poor preservation. The teeth of all three genera are described in detail, and a number of new parameters, such as crown stoutness and crown curvature, presented. A comprehensive structural and functional analysis indicates the skull is highly akinetic, and firmly internally braced. The superficial sutural pattern is adapted to resist deformation imposed by muscular action, particularly when feeding. The inference of strongly procumbent teeth in the short-snouted Callovian pliosaurs is shown to be based on the incorrect interpretation of badly crushed specimens. The skull musculature is reconstructed for the first time in a Callovian pliosaur, and an analysis of the lever systems exhibited by the jaws and muscles is presented. The adductor musculature is interpreted as a `geared' system providing mechanical advantage no matter where the teeth strike the prey, rather than the `snap and hold system' previously interpreted in non-Callovian pliosaurs. An analysis of tooth form, preserved stomach contents, and comparison with an existing model allows interpretation of prey preference and ecological position. Liopleurodon, and possibly Pachycostasaurus, are interpreted as shake and bolt feeding, high order predators of large boned, vertebrate prey. Simolestes is reinterpreted as an invertebrate feeder, possibly twist feeding, with a short, wide, high skull and a powerful bite. Comparison is made to the long-snouted genus Peloneustes which is considered ichthyophagous. The potential problems associated with a predominantly invertebrate diet are explored. Simolestes is interpreted as gaining a considerable electrolyte load through a diet of invertebrates. To avoid physiological problems Simolestesp robably possessedla rge, orbitally positioned, cephalic salt secreting glands. All Callovian pliosaur genera probably also possessed salt secreting glands, but of smaller size
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.341402  DOI: Not available
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