Sunday, April 03, 2011

A Tiny Maniraptoran From England

A tiny maniraptoran dinosaur in the Lower Cretaceous Hastings Group: Evidence from a new vertebrate-bearing locality in southeast England. 2011. D. Nash and S.C. Sweetman. Cretaceous Research, in press

Abstract [edit]: Here we report the cervical vertebra of a small dinosaur from the Pevensey Pit at Ashdown Brickworks, a site located north-west of Bexhill, East Sussex. The pit yields a rich assemblage of vertebrate fossils from the Valanginian Wadhurst Clay Formation of the Hastings Group.

The new specimen, a near-complete but water-worn posterior cervical vertebra, is tiny (total centrum length = 7.1 mm) but evidently from an adult theropod. Its large hypapophysis, X-shaped neural arch and amphicoelous centrum suggest referral to Maniraptora, and the subparallel anterior and posterior articular surfaces imply that it does not belong to a deinonychosaur. The X-shaped neural arch recalls a similar condition seen in oviraptorosaurs while the high neural canal/articular surface ratio (0.70) is bird-like.

The specimen is significant in representing the first maniraptoran to be reported from the Hastings Group but is otherwise indeterminate. By comparing the specimen to better known maniraptorans and estimating the proportions of the animal to which it belongs, we suggest that the total skeletal length of this maniraptoran was somewhere between 16 and 40 cm. It may therefore have been among the smallest of known Mesozoic dinosaurs.