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Postcranium of the paradigm elasmosaurid plesiosaurian Libonectes morgani (Welles, 1949)

Published online by Cambridge University Press:  20 November 2014

SVEN SACHS  and
BENJAMIN P. KEAR
SVEN SACHS*
Affiliation:
Im Hof 9, 51766 Engelskirchen, Germany
BENJAMIN P. KEAR
Affiliation:
Palaeobiology Programme, Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden
*
†Author for correspondence: sachs.pal@gmail.com
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Abstract

Elasmosauridae constitutes one of the most immediately recognizable plesiosaurian radiations. Their distinctive body plan represents the popular model for Plesiosauria, and is typified by an osteological morphology especially adapted for hyper-elongation of the neck. Nevertheless, many archetypal elasmosaurids are known only from incomplete and/or inadequately documented material, a problem that has contributed to their uncertain intra-clade relationships. A prime example of this is Libonectes morgani from the Upper Cretaceous of Texas, USA, which is frequently presented as an elasmosaurid structural proxy because of its three-dimensionally preserved holotype skull. Perplexingly though, both the taxonomic diagnosis and phylogenetic placement of L. morgani rely primarily upon the cervical vertebrae, together with the pectoral girdle and forelimb, yet most of these elements are now lost and figured only as line drawings. We therefore reviewed the remnant postcranial skeleton of L. morgani first-hand with the objective of clarifying its defining character states. Our observations showed that the existing diagnosis of L. morgani is indeed inadequate. Moreover, the only identifiable autapomorphies occurred within the axial skeleton. This concurred with an examination of character scores used in published plesiosaurian phylogenies, and highlights the persistent significance of postcranial elements for discriminating elasmosaurid taxa.

Keywords

Plesiosauriaaxial skeletonatlas-axis complexsystematics
Type
Original Articles
Information
Geological Magazine , Volume 152 , Issue 4 , July 2015 , pp. 694 - 710
Copyright
Copyright © Cambridge University Press 2014 

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