Metriorhynchidae


Metriorhynchidae is an extinct family of specialized, aquatic metriorhynchoid crocodyliforms from the Middle Jurassic to the Early Cretaceous period of Europe, North America and South America. The name Metriorhynchidae was coined by the Austrian zoologist Leopold Fitzinger in 1843. The group contains two subfamilies, the Metriorhynchinae and the Geosaurinae.

Description

Metriorhynchids are fully aquatic crocodyliforms. Their forelimbs were small and paddle-like, and unlike living crocodilians, they lost their osteoderms. Their body shape maximised hydrodynamy, as they did have a shark-like tail fluke.
Metriorhynchids were the only group of archosaurs to become fully adapted to the marine realm, becoming pelagic in lifestyle. With tail flukes, reduced limb musculature, and long bones histologically 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 the viviparous Keichousaurus, this has lent credence to the suggestion that metriorhynchids gave live birth. 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 external nares.
The family has a wide geographic distribution, with material found in Argentina, Chile, Cuba, England, France, Germany, Italy, Mexico, Poland, Russia and Switzerland.

Classification

analyses published during the 2000s cast doubt on the idea that many traditional metriorhynchid genera formed natural groups. The traditional species of Geosaurus, Dakosaurus and Cricosaurus 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. The monophyly of Metriorhynchus and Teleidosaurus is also unsupported, and the species of these genera are pending reclassification.
The classification presented by Young and Andrade in 2009 was approved in later studies of the Metriorhynchidae. Metriorhynchidae is a node-based taxon defined in 2009 as the least inclusive clade consisting of Metriorhynchus geoffroyii and Geosaurus giganteus. The cladogram below follows the topology from a 2020 analysis by Young et al. and reduced to genera only.

List of genera

The type genus of the family Metriorhynchidae is Metriorhynchus from the Middle to Late Jurassic. Other genera included within this family are Cricosaurus, Geosaurus, and Dakosaurus. Though once considered a metriorhynchid, Teleidosaurus has since been found to be slightly more distantly related to these animals within the superfamily Metriorhynchoidea.
Within this family, the genus Neustosaurus is considered nomen dubium.
The genus Capelliniosuchus was once thought to be a metriorhynchid similar to Dakosaurus. However, Sirotti demonstrated that it is a junior synonym of Mosasaurus.
GenusStatusAuthorAgeLocationDescriptionSynonymsImages

  • Aggiosaurus
Ambayrac, 1913late OxfordianFrance.Sometimes considered to be a nomen dubium.






  • Cricosaurus
ValidWagner, 1858middle Oxfordian to upper ValanginianArgentina, Chile, Cuba, England, France, Germany, Mexico, Russia and Switzerland.






  • Dakosaurus
Validvon Quenstedt, 1856lower Oxfordian to lower BerriasianArgentina, England, France, Germany, Mexico, Poland, Switzerland and possibly Russia.
  • Dacosaurus






  • Enaliosuchus
nomen dubiumKoken, 1883ValanginianGermany.-






  • Geosaurus
ValidCuvier, 1824upper Kimmeridgian to upper ValanginianFrance, Germany, Italy and Switzerland.
  • Brachytaenius
  • Halilimnosaurus






  • Gracilineustes
ValidYoung et al., 2010lower KimmeridgianEngland and France.






  • Maledictosuchus
ValidParrilla-Bel et al., 2013Spain.






  • Metriorhynchus
Validvon Meyer, 1830lower Callovian to upper Kimmeridgian.England, France, Germany and Switzerland.
  • Metiorychus






  • Neptunidraco
ValidCau & Fanti, 2011late Bajocian to earliest BathonianItaly.






  • Neustosaurus
nomen dubium— potential senior synonym of Cricosaurus





  • Plesiosuchus
ValidOwen, 1884late Kimmeridgian to early TithonianEngland and possibly Spain.






  • Purranisaurus
ValidRusconi, 1948lower Callovian to lower TithonianArgentina and Chile.






  • Rhacheosaurus
Validvon Meyer, 1831lower TithonianGermany.






  • Suchodus
ValidLydekker, 1890lower Callovian to lower OxfordianEngland and France.






  • Torvoneustes
ValidAndrade et al., 2010upper KimmeridgianEngland.






  • Tyrannoneustes
ValidYoung et al., 2013CallovianEngland.





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