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Abelisauroid dinosaur from the Middle Jurassic of England (Laurasia)



From: Ben Creisler
bcreisler@gmail.com

Another new paper not yet mentioned on the DML(link has photos):


Martín D. Ezcurra & Federico L. Agnolín (2012)
PalaeobiogeographyAn abelisauroid dinosaur from the Middle Jurassic of
Laurasia and its implications on theropod palaeobiogeography and
evolution.
Proceedings of the Geologists' Association (advance online publication)
http://dx.doi.org/10.1016/j.pgeola.2011.12.003
http://www.sciencedirect.com/science/article/pii/S0016787811001374



We review here the phylogenetic relationships of a theropod distal end
of tibia (MB. R.2351) from the Middle Jurassic Stonesfield Slate
(Taunton Formation, middle Bathonian) of Oxfordshire, England. This
specimen was previously described as a small basal tetanuran, but our
reinterpretation suggests that it was an early member of the
Abelisauroidea. The new assignment is supported by the presence of an
apomorphic vertical facet for the reception of the ascending process
of the astragalus, sub-rectangular anterior scar of the astragalar
ascending process, median vertical ridge in the scar for the reception
of the ascending process of the astragalus, and posterolateral process
not distinctly offset from the lateral margin of the shaft. In
particular, the Stonesfield specimen shares an overall morphology and
a unique combination of apomorphies with the Middle Jurassic
Australian abelisauroid Ozraptor. Nevertheless, both specimens differ
in some punctual features. MB. R.2351 constitutes the oldest evidence
of an abelisauroid outside Gondwana and indicates that the group had
achieved a Pangean distribution during, at least, the Middle Jurassic.
Thus, the initial diversification of abelisauroids would have occurred
earlier than previously thought. Accordingly, the Middle and Late
Jurassic Pangean distribution of abelisauroids implies that the
absence of the group in Cretaceous Asiamerican assemblages would
reflect a regional extinction, in which a competitive replacement with
coelurosaurs (e.g. tyrannosauroids) is surely one of the hypotheses
that should be tested in future studies.
 (