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Libonectes (elasmosaurid plesiosaur) re-examined

Ben Creisler

A new online paper:

Sven Sachs & Benjamin P. Kear (2014)
Postcranium of the paradigm elasmosaurid plesiosaurian Libonectes
morgani (Welles, 1949).
Geological Magazine (advanced online publication)
DOI: http://dx.doi.org/10.1017/S0016756814000636

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.