The Cranial Osteology and Feeding Ecology of the Metriorhynchid Crocodylomorph Genera Dakosaurus and Plesiosuchus from the Late Jurassic of Europe

YOUNG, M. T.; BRUSATTE, S. L. ; BRANDALISE DE ANDRADE, M.; DESOJO, J. B.; BEATTY, B. L.; STEEL, L.; FERNANDEZ, M. S; SAKAMOTO, M.; RUIZ-OMEÑACA; SCHOCH, R

PLOS ONE

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2012 vol. 7 p. 1 - 42

1932-6203

Background: Dakosaurus and Plesiosuchus are characteristic genera of aquatic, large-bodied, macrophagous metriorhynchidcrocodylomorphs. Recent studies show that these genera were apex predators in marine ecosystems during the latter partof 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 thetype species of both genera, and in doing so we resurrect the genus Plesiosuchus for the species Dakosaurus manselii. Bothspecies are diagnosed with numerous autapomorphies. Dakosaurus maximus has premaxillary ?lateral plates?; stronglyornamented maxillae; macroziphodont dentition; tightly fitting tooth-to-tooth occlusion; and extensive macrowear on themesial and distal margins. Plesiosuchus manselii is distinct in having: non-amblygnathous rostrum; long mandibularsymphysis; microziphodont teeth; tooth-crown apices that lack spalled surfaces or breaks; and no evidence for occlusal wearfacets. Our phylogenetic analysis finds Dakosaurus maximus to be the sister taxon of the South American Dakosaurusandiniensis, and Plesiosuchus manselii in a polytomy at the base of Geosaurini (the subclade of macrophagousmetriorhynchids 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 crownbreakage. Assuming this morphofunctional complex is indicative of diet, then Plesiosuchus would be a specialist feeding onother marine reptiles while Dakosaurus would be a generalist and possible suction-feeder. This hypothesis is supported byPlesiosuchus 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 trophicspecialisation enabled these two large-bodied species to coexist in the same ecosystem.