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Tyrannoneustes, oldest metriorhynchid super-predator crocodile



From: Ben Creisler
bcreisler@gmail.com


A new online paper:

Mark T. Young, Marco Brandalise de Andrade, Stephen L. Brusatte,
Manabu Sakamoto & Jeff Liston (2013)
The oldest known metriorhynchid super-predator: a new genus and
species from the Middle Jurassic of England, with implications for
serration and mandibular evolution in predacious clades.
Journal of Systematic Palaeontology (advance online publication)
DOI:10.1080/14772019.2012.704948
http://www.tandfonline.com/doi/full/10.1080/14772019.2012.704948


The Oxford Clay Formation of England has yielded numerous sympatric
species of metriorhynchid crocodylomorphs, although disagreement has
persisted regarding the number of valid species. For over 140 years
teeth reminiscent of the genus Dakosaurus have been known from the
Oxford Clay Formation but these have never been properly described and
their taxonomy and systematic affinity remain contentious.
Furthermore, an enigmatic mandible and associated postcranial skeleton
discovered by Alfred Leeds in the Fletton brick pits near Peterborough
also remains undescribed. We show that this specimen, and several
isolated teeth, represents the oldest known remains of a large-bodied
predatory metriorhynchid. This material is described herein and
referred to Tyrannoneustes lythrodectikos gen. et sp. nov. This
species has a unique occlusal pattern: the dentition was arranged so
that the posterior maxillodentary teeth interlock in the same plane
and occlude mesiodistally. It is the first described crocodylomorph
with microscopic denticles that are not contiguous along the carinae
(forming short series of up to 10 denticles) and do not noticeably
alter the height of the keel. Additionally, the dorsally expanded and
curved posterior region of the mandible ventrally displaced the
dentary tooth row relative to the jaw joint facilitating the
enlargement of the dentition and increasing optimum gape. Therefore,
Tyrannoneustes would have been a large-bodied marine predator that was
well-suited to feed on larger prey than other contemporaneous
metriorhynchids. A new phylogenetic analysis finds Tyrannoneustes to
be the sister taxon to the subclade Geosaurini. An isolated tooth,
humerus, and well-preserved mandible suggest a second species of
metriorhynchid super-predator may also have lived in the Oxford Clay
sea. Finally, we revise the diagnoses and descriptions of the other
Oxford Clay metriorhynchid species, providing a guide for
differentiating the many contemporaneous taxa from this exceptional
fossil assemblage.