Metriorhynchoid crocodylians represent the pinnacle of marine specialization within Archosauria. Not only were\ud they a major component of the Middle Jurassic–Early Cretaceous marine ecosystems, but they provide further\ud examples that extinct crocodilians did not all resemble their modern extant relatives. Here, we use a varied toolkit\ud of techniques, including phylogenetic reconstruction, geometric morphometrics, diversity counts, discrete character\ud disparity analysis, and biomechanical finite-element analysis (FEA), to examine the macroevolutionary history of\ud this clade. All analyses demonstrate that this clade became more divergent, in terms of biodiversity, form, and\ud function, up until the Jurassic–Cretaceous boundary, after which there is no evidence for recovery or further\ud radiations. A clear evolutionary trend towards hypercarnivory in Dakosaurus is supported by phylogenetic\ud character optimization, morphometrics, and FEA, which also support specialized piscivory within Rhacheosaurus\ud and Cricosaurus. Within Metriorhynchoidea, there is a consistent trend towards increasing marine specialization,\ud with the hypermarine Cricosaurus exhibiting numerous convergences with other Mesozoic marine reptiles (e.g. loss\ud of the deltopectoral crest and retracted external nares). In addition, biomechanics, morphometrics, and characterdisparity\ud analyses consistently distinguish the two newly erected metriorhynchid subfamilies. This study illustrates\ud that together with phylogeny, quantitative assessment of diversity, form, and function help elucidate the\ud macroevolutionary pattern of fossil clades

The holotype and referred specimens of Geosaurus giganteus, a metriorhynchid crocodile from the Tithonian (Upper Jurassic) of Germany, is redescribed, along with a historical overview of the genus and species. This taxon is unique among metriorhynchids as its serrated, strongly lateromedially compressed dentition is arranged as opposing blades, suggesting it was adapted to efficiently slice through fleshy prey. A new phylogenetic analysis of Crocodylomorpha is presented, which finds G. giganteus to be nested within what is currently considered Dakosaurus, whereas the other species currently assigned to Geosaurus form a clade with Enaliosuchus and the holotype of Cricosaurus. The phyletic relationship of G. giganteus with other metriorhynchids indicates that the current definition of the genus Geosaurus is polyphyletic, and that the inclusion of subsequent longirostrine species to this genus is in error. The re-analysis presented herein demonstrates Geosaurus to be composed of three species sensu stricto. The appropriate taxonomic amendments to the Metriorhynchidae are also provided.

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.

Machimosaurus was a large-bodied genus of teleosaurid crocodylomorph, considered to have been durophagous/chelonivorous, and which frequented coastal marine/estuarine ecosystems during the Late Jurassic. Here, we revise the genus based on previously described specimens and revise the species within this genus. We conclude that there were three European Machimosaurus species and another taxon in Ethiopia. This conclusion is based on numerous lines of evidence: craniomandibular, dental and postcranial morphologies; differences in estimated total body length; geological age; geographical distribution; and hypothetical lifestyle. We re-diagnose the type species Machimosaurus hugii and limit referred specimens to only those from Upper Kimmeridgian–Lower Tithonian of Switzerland, Portugal and Spain. We also re-diagnose Machimosaurus mosae, demonstrate that it is an available name and restrict the species to the uppermost Kimmeridgian–lowermost Tithonian of northeastern France. We re-diagnose and validate the species Machimosaurus nowackianus from Harrar, Ethiopia. Finally, we establish a new species, Machimosaurus buffetauti, for the Lower Kimmeridgian specimens of France and Germany (and possibly England and Poland). We hypothesize that Machimosaurus may have been analogous to the Pliocene–Holocene genus Crocodylus in having one large-bodied taxon suited to traversing marine barriers and additional, geographically limited taxa across its range.

A new species, Goniopholis kiplingi sp. nov., based on an exceptionally preserved skull from the Lower Cretaceous of England is described in detail. It shows great similarity with Goniopholis simus and Goniopholis baryglyphaeus, but can be distinguished by the presence of longer lachrymals, smooth (not edged) dorsal surface of the quadrate, and proportionally longer rostrum. A comprehensive phylogenetic analysis of Mesoeucrocodylia (104 taxa; 486 characters) focused on goniopholidids (14 species) places G. kiplingi as sister‐group of G. simus, and as part of a monophyletic group also containing G. baryglyphaeus. The relationships of Nannosuchus gracilidens and three undescribed European taxa are explored, and preliminary analyses of Denazinosuchus kirtlandicus (Upper Cretaceous, USA) and ‘Goniopholis’ phuwiangensis (Lower Cretaceous, Thailand) are presented. The assignment of taxa to the genus Goniopholis is discussed. Goniopholis, in its traditional sense, is considered paraphyletic and a restricted updated definition is proposed, with comments on the evolution of other goniopholidids. Morphological characteristics of fragmentary material attributed to Goniopholis are not considered sufficient to secure their generic/specific assignment, and provide no support for the presence of Goniopholis in Gondwanan and/or Upper Cretaceous sedimentary units. Currently Goniopholis is restricted to the Upper Jurassic−Lower Cretaceous of Europe. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, S66–S108.