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

Abstract

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 FindingsHere 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/SignificanceThe 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.

Sea surface temperature contributes to marine crocodylomorph evolution

“…An additional approach was applied to this generic data set for further refinement of the diversity: phylogenetic correction, superimposed on the stratigraphy by filling ghost ranges of genera (Supplementary Data 1). Phylogenetic corrections follow the topology recovered for Thalattosuchia 31 and the topology recovered for Dyrosauridae 34 . Pholidosauridae (two marine genera) are, in comparison with Thalattosuchia and Dyrosauridae, a relatively small marine radiation with a larger ancestral freshwater stock.…”

“…To reduce taxonomic bias as much as possible, another set of data considered only genera. This is because across the different lineages of marine crocodylomorphs considered here, two have recently been revised in depth leading to a burst of previously overlooked species diversity 31 . Species diversity, and to a lesser extent generic diversity, are unbalanced when comparing recently revised groups such as metriorhynchoids or dyrosaurids, versus other groups such as the Teleosauridae, whose taxonomic content has not been revised recently 32,33 .…”

A Jurassic pleuropholid fish (Teleostei, Pleuropholidae) in the Tethys Sea domain of North America

“…Andrade (2009) andYoung et al (2012) placed these species in the genus Cricosaurus Wagner, 1858, as C. vignaudi andC. saltillense, respectively.…”

Reptiles Extintos - Volumen en Homenaje a Zulma Gasparini

“…Upper Kimmeridgian, Staufenbei Giengen, Baden-Württemberg, Germany. Vignaud and Gasparini, 1996 Young et al, 2012;Wilberg, 2015). Based on skull length of MOZ-PV 6146, the body length estimation is 4.20 m (Herrera, 2012).…”

“…The skull is incompletely preserved, thus an estimation of body length can not be made. several taxa have been found (e.g., Gasparini and IturraldeVinent, 2001;Buchy et al, 2007;Buchy, 2008;Young et al, 2012Young et al, , 2013. In Patagonia, Oxfordian-Early Kimmeridgian marine levels are restricted to marine platform limestones Some undescribed Patagonian specimens need to be described.…”