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Hastanectes. new leptocleidid plesiosaur from Early Cretaceous of England



From: Ben Creisler
bcreisler@gmail.com


A new plesiosaur taxon in an online paper.



Roger B. J. Benson, Hilary F. Ketchum, Darren Naish & Langan E. Turner (2012)
A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis
Formation (Early Barremian–early Aptian; Early Cretaceous) of the Isle
of Wight and the evolution of Leptocleididae, a controversial clade
Journal of Systematic Palaeontology (advance online publication)
DOI:10.1080/14772019.2011.634444
http://www.tandfonline.com/doi/full/10.1080/14772019.2011.634444

Among the most enigmatic and controversial plesiosaurian clades is the
Early Cretaceous Leptocleididae, a small group of (mostly)
short-necked taxa with ‘intermediate’ or ‘pliosauromorph’ body
proportions. Leptocleidids have often been interpreted as basal
members of Pliosauroidea, and their presence in marginal marine and
even freshwater facies has led to suggestions that they might
represent late-surviving relicts, perhaps related to the Lower
Jurassic rhomaleosaurids. We describe a new leptocleidid, Vectocleidus
pastorum gen. et sp. nov., from the late Barremian part of the
Cowleaze Chine Member (Vectis Formation), Isle of Wight, UK, and
undertake a detailed reassessment of leptocleidid anatomy and
relationships. New data on the long-necked Brancasaurus gives extra
support to a monophyletic Leptocleididae with taxa of ‘intermediate’
body plan and robust skulls, Leptocleidus superstes, Leptocleidus
capensis, Nichollssaura and Vectocleidus. Thus, leptocleidids adopted
a range of body plans on the pliosauromorph–plesiosauromorph spectrum.
Support for a placement of Leptocleididae within Pliosauroidea is
weak, and most proposed synapomorphies fail the test of similarity.
However, numerous synapomorphies, including many new observations,
support a derived position within Plesiosauroidea. Thus, the
‘intermediate’ body plan of many leptocleidids is not plesiomorphic,
and plesiosaurian body plan evolution was complex and highly plastic.
We also summarize the anatomy of ‘Cimoliasaurus’ valdensis, a
short-necked Early Cretaceous taxon. ‘C.’ valdensis is a valid taxon
for which we erect the new monotypic genus Hastanectes. Hastanectes
shows evidence of possible pliosaurid affinities. Thus, multiple
plesiosaurian clades may have invaded margin and freshwater
environments.

http://zoobank.org/urn:lsid:zoobank.org:pub:8A0A8BD0-F6BB-4F74-BB18-79CBBA2F105