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Metriorhynchus is an extinct genus of marine crocodyliformes that lived in the oceans during the Late Jurassic. The type species, M. brevirostris was named in 1829 as a species of Steneosaurus before being named as a separate genus by the Germans palaeontologist Christian von Meyer in 1832. The name Metriorhynchus means "moderate snout", and is derived from the Ancient Greek Metrio- ("moderate") and - rhynchos ("snout").
The earliest discovered specimen of Metriorhynchus brevirostris is MNHN.F.RJN 116, a jaw collected from the Marnes de Villers by Charles Bacheley during the early 1770s, who believed it belonged to a fish in 1778 and then a dolphin or a sperm whale in 1808,Bacheley, C. (1778) Notice des pétrifications & autres faits d’histoire naturelle qui se trouvent le long des côtes du Pays d’Auge. In: Lépecq de la Clôture, L. Collection d’observations sur les maladies et constitutions épidémiques. Rouen: Imprimerie privilégiée, pp. 357–359.Brignon, A. (2016) Abbé Bacheley and the discovery of the first dinosaurs and marine crocodilians from the Jurassic of the Vaches Noires (Callovian/Oxfordian, Normandy, France). Comptes Rendus Palevol 15 : 595–605 (in French with an abridged English version). that was described by Georges Cuvier (1808).Cuvier, G. (1808). Sur les ossemens fossiles de crocodiles, et particulièrement sur ceux des environs du Havre et de Honfleur, avec des remarques sur les squelettes des sauriens de la Thuringe. Annales du Muséum d’Histoire Naturelle 12: 73–110, pl. 10–11. The holotype of M. brevirostris is MHNG V02232, a partial rostrum from Le Havre, and Georges Cuvier mentioned that it was in the collection of the Museum of the Academy of Geneva in 1811.Cuvier, G. (1824). Recherches sur les ossemens fossiles, où l’on rétablit les caractères de plusieurs animaux dont les révolutions du globe ont détruit les espèces, nouvelle édition, 2e partie, Vol. 5. Paris: G. Dufour et E. d’Ocagne. In 1824, Cuvier then described multiple "Gharial" remains and came to the now-incorrect conclusion that he was describing two species (what would later become Metriorhynchus and Streptospondylus); Cuvier had also grouped into the remains the lectotype of Steneosaurus.
When naming Steneosaurus in 1825, Étienne Geoffroy Saint-Hilaire created two species for the genus: Steneosaurus rostro-major (now S. rostromajor) and S. rostro-minor.Geoffroy Saint-Hilaire, É. (1825) Recherches sur l’organisation des gavials, sur leurs affinités naturelles desquelles résulte la nécessité d’une autre distribution générique: Gavialis, Teleosaurus, Steneosaurus; et sur cette question, si les gavials (Gavialis), aujourd’hui répandus dans les parties orientales de l’Asie, descendent, par voie non interrompue de génération, des gavials antidiluviens, soit des gavials fossiles, dits crocodiles de Caen ( Teleosaurus), soit des gavials fossiles du Havre et de Honfleur ( Steneosaurus). Mémoires du Muséum d’Histoire Naturelle 12: 97–155, pl. 5–6. He assigned MNHN.F.RJN 116 to S. rostro-major and Friedrich Holl created Steneosaurus brevirostris in 1829 to solely classify MHNG V02232.Holl, F. (1829). Handbuch der Petrefactenkunde Teil 1.Dresden: Hilscher, 416. In 1831, John Edward Gray instead assigned the specimen to the gharial species Gavialis jurinii.Gray, J.E. (1831) Synopsis reptilium or short descriptions of the species of reptiles. Part I: Cataphracta, tortoises, crocodiles, and enaliosaurians. London: Treuttel, Wurz & Co., 85. The next year, Hermann von Meyer separated Cuvier's two "gharial" species and created Metriorhynchus brevirostris, Metriorhynchus geoffroyi (to house MHNG V02232) and Streptospondylus altdorfensis (now recognised as a Theropoda dinosaur). Amongst the splitting of the "gavial" species, von Meyer (1832) incorrectly placed MNHN.F.RJN 116 within S. altdorfensis.
François Jules Pictet suggested that Metriorhynchus was a synonym of Steneosaurus and in 1845 was the first author to invalidate S. rostro-minor as a species.Pictet, F.J. (1845). Traité élémentaire de paléontologie ou histoire naturelle des animaux fossiles considérés dans leurs rapports zoologiques et géologiques, tome 2.Paris: Langlois et Leclerq. Metriorhynchus as a genus was later reinstated, and Eugène Eudes-Deslongchamps (1867–69) recognized four Callovian species of Metriorhynchus: M. superciliosus, M. moreli, M. blainvillei, and M. brachyrhynchus, and he also standardised the use of the genus name Metriorhynchus.
Richard Lydekker in 1888a suggested it to be "advisable" to retain the name Metriorhynchus,Lydekker, R. (1888a). Catalogue of the fossil Reptilia and Amphibia in the British Museum (Natural History), Cromwell Road, S.W., Part 1. Containing the orders Ornithosauria, Crocodilia, Dinosauria, Squamata, Rhynchocephalia, and Proterosauria. London: British Museum of Natural History, 309. and in 1889a he suggested that Metriorhynchus was similar to Cricosaurus and therefore he concluded the genus was crocodilian.Lydekker, R. (1889). On the remains and affinities of five genera of Mesozoic reptiles. Quarterly Journal of the Geological Society 45: 41–59. Steel moved MHNG V02232 back into Metriorhynchus geoffroyii in 1973.
Young et al. (2010) was the first to restrict M. brevirostris by re-assigning specimens to other genera, and MHNG V02232 was designated as the holotype of M. brevirostris by Young et al. (2019). Young et al. (2019) also synonymised M. geoffroyii with M. brevirostris and reassigned MNHN.F.RJN 116 to M. brevirostris.
The genera Purranisaurus and Suchodus have been considered junior synonyms of Metriorhynchus.Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag,116 pp. Recent phylogenetic analyses however, do not support the monophyly of Metriorhynchus, as believed during the 1860s-2010.Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology 27 (3): 170A.
Eudes-Deslongchamps (1867–69) recognized four Callovian species of Metriorhynchus: M. superciliosus, M. moreli, M. blainvillei, and M. brachyrhynchus.Eudes-Deslongchamps E. (1867-1869). Notes Paléontologiques. Caen and Paris: 320-392. Later, Andrews (1913) considered there to be seven valid species: M. superciliosus, M. moreli, M. brachyrhynchus, M. durobrivensis, M. cultridens, M. leedsi and M. laeve.Andrews CW. 1913. A descriptive catalogue of the marine reptiles of the Oxford Clay, Part Two. London: British Museum (Natural History), 206 pp. However, Adams-Tresman (1987), using linear morphometrics, could only distinguish between the two skull groups, so she found there to be two species from the Oxford Clay, M. superciliosus and M. brachyrhynchus.Adams-Tresman SM. 1987. The Callovian (Middle Jurassic) marine crocodile Metriorhynchus from Central England. Palaeontology 30 (1): 179-194. Vignaud (1997) however, considered there to be three Callovian species: M. superciliosus, M. brachyrhynchus and M. leedsi,Vignaud P. (1997). La morphologie dentaire des Thalattosuchia (Crocodylia, Mesosuchia). Palaeovertebrata 26: 35-59. and a 2022 study describing a new metriorhynchid specimen advocated returning to this taxonomic system, considering Gracilineustes and Thalattosuchus junior synonyms of Metriorhynchus.
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