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Dakosaurus and Plesiosuchus (Thalattosuchia) skull osteology and feeding



From: Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:

Mark T. Young, Stephen L. Brusatte, Marco Brandalise de Andrade, Julia
B. Desojo, Brian L. Beatty, Lorna Steel, Marta S. Fernández, Manabu
Sakamoto, Jose Ignacio Ruiz-Omeñaca & Rainer R. Schoch (2012)
The Cranial Osteology and Feeding Ecology of the Metriorhynchid
Crocodylomorph Genera Dakosaurus and Plesiosuchus from the Late
Jurassic of Europe.
PLoS ONE 7(9): e44985.
doi:10.1371/journal.pone.0044985
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0044985



Background

Dakosaurus and Plesiosuchus are characteristic genera of aquatic,
large-bodied, macrophagous metriorhynchid crocodylomorphs. Recent
studies show that these genera were apex predators in marine
ecosystems during the latter part of the Late Jurassic, with robust
skulls and strong bite forces optimized for feeding on large prey.

Methodology/Principal Findings

Here we present comprehensive osteological descriptions and systematic
revisions of the type species of both genera, and in doing so we
resurrect the genus Plesiosuchus for the species Dakosaurus manselii.
Both species are diagnosed with numerous autapomorphies. Dakosaurus
maximus has premaxillary ‘lateral plates’; strongly ornamented
maxillae; macroziphodont dentition; tightly fitting tooth-to-tooth
occlusion; and extensive macrowear on the mesial and distal margins.
Plesiosuchus manselii is distinct in having: non-amblygnathous
rostrum; long mandibular symphysis; microziphodont teeth; tooth-crown
apices that lack spalled surfaces or breaks; and no evidence for
occlusal wear facets. Our phylogenetic analysis finds Dakosaurus
maximus to be the sister taxon of the South American Dakosaurus
andiniensis, and Plesiosuchus manselii in a polytomy at the base of
Geosaurini (the subclade of macrophagous metriorhynchids that includes
Dakosaurus, Geosaurus and Torvoneustes).

Conclusions/Significance

The sympatry of Dakosaurus and Plesiosuchus is curiously similar to
North Atlantic killer whales, which have one larger ‘type’ that lacks
tooth-crown breakage being sympatric with a smaller ‘type’ that has
extensive crown breakage. Assuming this morphofunctional complex is
indicative of diet, then Plesiosuchus would be a specialist feeding on
other marine reptiles while Dakosaurus would be a generalist and
possible suction-feeder. This hypothesis is supported by Plesiosuchus
manselii having a very large optimum gape (gape at which multiple
teeth come into contact with a prey-item), while Dakosaurus maximus
possesses craniomandibular characteristics observed in extant
suction-feeding odontocetes: shortened tooth-row, amblygnathous
rostrum and a very short mandibular symphysis. We hypothesise that
trophic specialisation enabled these two large-bodied species to
coexist in the same ecosystem.