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Marmornectes, new plesiosaur from England



From: Ben Creisler
bh480@scn.org

This new plesiosaur has been on the Web for a couple of weeks. Before
people who attended the SVP meeting start posting about the talks, I
thought I might get this one in.

Ketchum, Hilary F.  & Benson, Roger B. J.  (2011)
A new pliosaurid (Sauropterygia, Plesiosauria) from the Oxford Clay
Formation (Middle Jurassic, Callovian) of England: evidence for a gracile,
longirostrine grade of Early?Middle Jurassic pliosaurids.
Special Papers in Palaeontology (Studies on Fossil Tetrapods) 86: 109-129
doi:10.1111/j.1475-4983.2011.01083.x
http://www.palass.org/beta/eps/shop/product/sp-studies-on-fossil-tetrapods/
http://datadryad.org/handle/10255/dryad.34260?show=full

A partial skeleton from the Sigiloceras enodatum ammonite Subzone (early
Callovian, Middle Jurassic) of the Oxford Clay Formation of Quest Pit, near
Stewartby, Bedfordshire, UK respresents one of the basalmost Middle
Jurassic pliosaurids. Marmornectes candrewi gen. et sp. nov. possesses
seven autapomorphies and a longirostrine snout. Reassessment of pliosauroid
relationships demonstrates that Thalassiodracon hawkinsii, Hauffiosaurus
spp. and Attenborosaurus conybeari are successively more derived basal
representatives of Pliosauridae. This indicates that a longirostrine snout
was acquired among Early Jurassic pliosaurids (such as Hauffiosaurus), but
that these early taxa had a small body size, long neck, and gracile skull
and limb bones relative to the contemporaneous rhomaleosaurids, which were
robust, large-bodied macropredators. The pliosaurid lineage only acquired
its ?characteristic? large size, robust skull and short neck in the late
Middle Jurassic after the extinction of Rhomaleosauridae.

Type specimen:  BEDFM 1999.201, a partial skeleton. Its type locality is
Quest Pit, east of Stewartby, which is in a Callovian marine mudstone in
the Oxford Clay Formation of the United Kingdom. 


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