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Stratesaurus (UK Lower Jurassic plesiosaur) anatomy

Ben Creisler

 A new online paper:

Roger B J. Benson, Mark Evans & Michael A. Taylor (2015)
The anatomy of Stratesaurus (Reptilia, Plesiosauria) from the
lowermost Jurassic of Somerset, United Kingdom.
Journal of Vertebrate Paleontology (advance online publication)

We provide a complete description of one of the oldest plesiosaurians,
Stratesaurus taylori from the earliest Hettangian of the United
Kingdom. At least 25 apomorphies distinguish S. taylori from the
sympatric Thalassiodracon hawkinsii, to which all three specimens of
S. taylori were originally referred. Several features of the skull of
S. taylori suggest specialization on small prey items, or sieve
feeding. In particular, it has anteriorly inclined premaxillary and
mesial maxillary teeth and an only weakly heterodont maxillary
dentition. This indicates niche partitioning among sympatric
small-bodied plesiosaurians: T. hawkinsii has a pronouncedly
heterodont dentition. With a body length estimated around 2 m, S.
taylori is one of the smallest plesiosaurians, comparable to T.
hawkinsii. Our anatomical review of S. taylori suggests difficulty
determining its precise phylogenetic affinities. This is consistent
with a general lack of phylogenetic resolution among earliest Jurassic
plesiosaurians, which may result from missing data on their Triassic
ancestry. However, due to its plesiomorphic morphology and
well-characterized anatomy, we recommend S. taylori as an ingroup
representative of Plesiosauria for future cladistic analyses of
Triassic sauropterygians.