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New species of Torvoneustes (metriorhynchid crocodylomorph) from Upper Jurassic of England



From: Ben Creisler
bcreisler@gmail.com

A recent paper not yet mentioned on the DML:

Mark T. Young, Marco Brandalise De Andrade, Steve Etches & Brian L.
Beatty (2013)
Zoological Journal of the Linnean Society 169 (4): 820–848
A new metriorhynchid crocodylomorph from the Lower Kimmeridge Clay
Formation (Late Jurassic) of England, with implications for the
evolution of dermatocranium ornamentation in Geosaurini.
DOI: 10.1111/zoj.12082
http://onlinelibrary.wiley.com/doi/10.1111/zoj.12082/abstract


A new metriorhynchid crocodylomorph from the Lower Kimmeridge Clay
Formation (Kimmeridgian, Upper Jurassic) of England is described. This
specimen, a three-dimensionally preserved skull and left mandibular
ramus, is referred to a new species: Torvoneustes coryphaeus sp. nov.
Within the genus Torvoneustes, T. coryphaeus sp. nov. is unique as it
has a long anteromedial process of the frontal, ornamented
dermatocranium, and the supraorbital notch forms a strongly acute
angle. Our phylogenetic analysis confirms the placement of this
specimen in Torvoneustes. The dentition of T. coryphaeus sp. nov.,
like that of the type species, has a blunt apex, crown basal–mid
regions with numerous tightly packed apicobasally aligned ridges, and
apical region with an anastomosed pattern of ridges that interact with
the carinae. Within Thalattosuchia these dental characteristics are
only found in Torvoneustes and the teleosaurid Machimosaurus. The
heavily ornamented dermatocranium of T. coryphaeus sp. nov. is in
contrast to the unornamented (nasals and frontal)–lightly ornamented
(maxillae and premaxillae) pattern seen in Torvoneustes carpenteri.
Curiously, this pattern of reduction and loss of dermatocranium
ornamentation is also observed in Metriorhynchus, Dakosaurus, and the
subclade Rhacheosaurini. We hypothesize that the ‘smooth’
dermatocranium of Late Jurassic metriorhynchids evolved independently
in each subclade (parallel evolution), and would have reduced drag,
thereby making locomotion through water more energy efficient.