Metriorhynchids are fully aquaticcrocodyliforms. Their forelimbs were small and paddle-like, and unlike livingcrocodylians, they lost theirosteoderms ("armour scutes"). Their body shape maximisedhydrodynamy (swimming efficiency), as they did have a shark-like tail fluke.[6] Likeichthyosaurs andplesiosaurs, metriorhynchids developed smooth, scaleless skin.[7]
Metriorhynchids were the only group ofarchosaurs to become fully adapted to the marine realm, becomingpelagic in lifestyle.[8] With tail flukes, reduced limb musculature, and long boneshistologically comparable to other obligately aquatic animals, they were almost certainly incapable of terrestrial locomotion; combined with an unusually tall hip opening, as also seen in other obligately aquatic reptiles including theviviparousKeichousaurus, these characters suggest that metriorhynchids gave live birth.[9] A fossil of a pregnantDakosaurus female recovered from the Late Jurassicplattenkalk, Bavaria, preserves the complete skeleton of a neonate with small, paddle-like forelimbs unsuited for walking on land, similar to those of adults, further supporting live birth in metriorhynchids.[10][11] Recent research posits that despite their successful adaptation to a pelagic lifestyle,basal metriorhynchids were uniquely disadvantaged among aquatic tetrapods in evolving into sustained swimmers due to little to no posterodorsal retraction of the externalnares (unlike other reptilian groups such asmesosaurs,phytosaurs,thalattosaurians,saurosphargids,ichthyosauriforms,sauropterygians,pleurosaurids ormosasauroids, as well as mammaliancetaceans orsirenians).[12] The family has a wide geographic distribution, with material found inArgentina,Chile,Cuba,England,France,Germany,Italy,Mexico,Poland,Russia,Switzerland andCzech Republic.[8][5][13]
Phylogenetic analyses published during the 2000s cast doubt on the idea that many traditional metriorhynchid genera formed natural groups (i.e., include all descendants of a common ancestor). The traditional species ofGeosaurus,[14][15][16]Dakosaurus[14] andCricosaurus[14] were found to represent unnatural groups, and the species traditionally classified in these genera were reshuffled in a study published in November 2009 by Mark T. Young and Marco Brandalise de Andrade.[4] Themonophyly ofMetriorhynchus[14][15][17] andTeleidosaurus[14][16] is also unsupported, and the species of these genera are pending reclassification.[4]
^Andrews, CW. (1913).A descriptive catalogue of the marine reptiles of the Oxford Clay, Part Two. London: British Museum (Natural History). p. 206.
^Alfio A. Chiarenza; Davide Foffa; Mark T. Young; Gianni Insacco; Andrea Cau; Giorgio Carnevale; Rita Catanzariti (2015). "The youngest record of metriorhynchid crocodylomorphs, with implications for the extinction of Thalattosuchia".Cretaceous Research.56:608–616.Bibcode:2015CrRes..56..608C.doi:10.1016/j.cretres.2015.07.001.hdl:2318/1537833.
^Fitzinger LJFJ. 1843.Systema Reptilium. Wien: Braumüller et Seidel, 106 pp.
^Fraas E (1902). "Die Meer-Krocodilier (Thalattosuchia) des oberen Jura unter specieller Berücksichtigung vonDacosaurus undGeosaurus".Palaeontographica.49:1–72.
^abcdeYoung MT (2007). "The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia)".Journal of Vertebrate Paleontology.27 (3): 170A.doi:10.1080/02724634.2007.10010458.
^abAndrea Cau; Federico Fanti (2011). "The oldest known metriorhynchid crocodylian from the Middle Jurassic of North-eastern Italy:Neptunidraco ammoniticus gen. et sp. nov".Gondwana Research.19 (2):550–565.Bibcode:2011GondR..19..550C.doi:10.1016/j.gr.2010.07.007.
^abYoung, M.T., Brignon, A., Sachs, S., Hornung J.J., Foffa, D., Kitson, J.J.N., Johnson, M.M., Steel, L. (November 2020). "Cutting the Gordian knot: a historical and taxonomic revision of the Jurassic crocodylomorphMetriorhynchus".Zoological Journal of the Linnean Society.192 (2):510–553.doi:10.1093/zoolinnean/zlaa092.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Stéphane Hua (May 2020). "A new specimen ofTeleidosaurus calvadosii (Eudes-Deslongchamps, 1866) (Crocodylia, Thalattosuchia) from the Middle Jurassic of France".Annales de Paléontologie.106 (4).Bibcode:2020AnPal.10602423H.doi:10.1016/j.annpal.2020.102423.
^Buffetaut E (1982). "Radiation évolutive, paléoécologie et biogéographie des Crocodiliens mésosuchienes".Mémoires de la Société Géologique de France.142:1–88.
^Simonelli V (1896). "Intoro agli avanzi di coccodrilliano scoperti a San Valentino (provincial di Reggio Emilia) nel 1886".Atli della Reale Accademia dei Lincei, Series Qunita Rendiconti.5 (2):11–18.
^Cuvier G. 1824. Sur les ossements fossiles de crocodiles, 5. In: Dufour & D'Occagne, eds.Recherches sur les ossements fossiles, 2nd édition. Paris: 143-160
^Andrade, M.B.D.; Young, M.T.; Desojo, J.B.; Brusatte, S.L. (2010). "The evolution of extreme hypercarnivory in Metriorhynchidae (Mesoeucrocodylia: Thalattosuchia) based on evidence from microscopic denticle morphology".Journal of Vertebrate Paleontology.30 (5):1451–1465.Bibcode:2010JVPal..30.1451D.doi:10.1080/02724634.2010.501442.hdl:11336/69039.S2CID83985855.
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