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

<div><h3>Background</h3><p><em>Dakosaurus</em> and <em>Plesiosuchus</em> 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.</p> <h3>Methodology/Principal Findings</h3><p>Here we present comprehensive osteological descriptions and systematic revisions of the type species of both genera, and in doing so we resurrect the genus <em>Plesiosuchus</em> for the species <em>Dakosaurus manselii</em>. Both species are diagnosed with numerous autapomorphies. <em>Dakosaurus maximus</em> has premaxillary ‘lateral plates’; strongly ornamented maxillae; macroziphodont dentition; tightly fitting tooth-to-tooth occlusion; and extensive macrowear on the mesial and distal margins. <em>Plesiosuchus manselii</em> 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 <em>Dakosaurus maximus</em> to be the sister taxon of the South American <em>Dakosaurus andiniensis</em>, and <em>Plesiosuchus manselii</em> in a polytomy at the base of Geosaurini (the subclade of macrophagous metriorhynchids that includes <em>Dakosaurus</em>, <em>Geosaurus</em> and <em>Torvoneustes</em>).</p> <h3>Conclusions/Significance</h3><p>The sympatry of <em>Dakosaurus</em> and <em>Plesiosuchus</em> 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 <em>Plesiosuchus</em> would be a specialist feeding on other marine reptiles while <em>Dakosaurus</em> would be a generalist and possible suction-feeder. This hypothesis is supported by <em>Plesiosuchus manselii</em> having a very large optimum gape (gape at which multiple teeth come into contact with a prey-item), while <em>Dakosaurus maximus</em> 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.</p>