Metriorhynchidae Explained

Metriorhynchidae is an extinct family of specialized, aquatic metriorhynchoid crocodyliforms from the Middle Jurassic to the Early Cretaceous period (Bajocian to early Aptian^[1]) of Europe, North America and South America. The name Metriorhynchidae was coined by the Austrian zoologist Leopold Fitzinger in 1843.^[2] The group contains two subfamilies, the Metriorhynchinae and the Geosaurinae.^{[3] [4]} They represent the most marine adapted of all archosaurs.

Description

Metriorhynchids are fully aquatic crocodyliforms. Their forelimbs were small and paddle-like, and unlike living crocodylians, they lost their osteoderms ("armour scutes"). Their body shape maximised hydrodynamy (swimming efficiency), as they did have a shark-like tail fluke.^[5] Like ichthyosaurs and plesiosaurs, metriorhynchids developed smooth, scaleless skin.^[6]

Metriorhynchids were the only group of archosaurs to become fully adapted to the marine realm, becoming pelagic in lifestyle.^[7] 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, these characters suggest that metriorhynchids gave live birth.^[8] A fossil of a pregnant Dakosaurus female recovered from the Late Jurassic plattenkalk, 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.^{[9] [10]} 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 (unlike other reptilian groups such as mesosaurs, phytosaurs, thalattosaurians, saurosphargids, ichthyosauriforms, sauropterygians, pleurosaurids or mosasauroids, as well as mammalian cetaceans or sirenians).^[11] The family has a wide geographic distribution, with material found in Argentina, Chile, Cuba, England, France, Germany, Italy, Mexico, Poland, Russia, Switzerland and Czech Republic.^[12]

Classification

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 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.^[3] The monophyly of Metriorhynchus^{[13] [14] [15]} and Teleidosaurus^{[13] [16]} is also unsupported, and the species of these genera are pending reclassification.^[3]

The classification presented by Young and Andrade in 2009 was approved in later studies of the Metriorhynchidae.^{[4] [17] [18]} Metriorhynchidae is a node-based taxon defined in 2009 as the least inclusive clade consisting of Metriorhynchus geoffroyii and Geosaurus giganteus.^[3] The cladogram below follows the topology from the 2020 analyses by Young et al. and reduced to genera only.^[19]

List of genera

The type genus of the family Metriorhynchidae is Metriorhynchus from the Middle to Late Jurassic.^[19] 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.^[20]

Within this family, the genus Neustosaurus and Enaliosuchus are considered nomen dubium ("doubtful name").^[21]

The genus Capelliniosuchus was once thought to be a metriorhynchid similar to Dakosaurus.^[22] However, it was later found to be a mosasaur.^[23]

Genus	Status	Author	Age	Location	Description	Synonyms	Images
Aggiosaurus		Ambayrac, 1913	late Oxfordian	France.	Sometimes considered to be a nomen dubium.
Cricosaurus	Valid	Wagner, 1858	middle Oxfordian to upper Valanginian	Argentina, Chile, Cuba, England, France, Germany, Mexico, Russia and Switzerland.
Dakosaurus^[24]	Valid	von Quenstedt, 1856	upper Kimmeridgian to lower Berriasian	Argentina, England, France, Germany, Mexico, Poland, Switzerland and possibly Russia.		Dacosaurus (lapsus calami)
Enaliosuchus^[25]	nomen dubium^[26]	Koken, 1883	Valanginian	Germany.
Geosaurus^[27]	Valid	Cuvier, 1824	upper Kimmeridgian to upper Valanginian	France, Germany, Italy and Switzerland.		Brachytaenius Halilimnosaurus
Gracilineustes^[28]	Valid	Young et al., 2010	middle Callovian to lower Kimmeridgian	England and France.
Maledictosuchus	Valid	Parrilla-Bel et al., 2013	middle Callovian to Kimmeridgian	Spain and Mexico.
Metriorhynchus	Valid	von Meyer, 1832	lower Kimmeridgian.	France.		Metiorychus (lapsus calami)
Neptunidraco	Valid	Cau & Fanti, 2011	earliest Bathonian	Italy.
Neustosaurus	nomen dubium		Valanginian		- potential senior synonym of Enaliosuchus
Plesiosuchus	Valid	Owen, 1884	late Kimmeridgian to early Tithonian	England and possibly Spain.
Purranisaurus	Valid	Rusconi, 1948	upper Tithonian	Argentina and Chile.
Rhacheosaurus	Valid	von Meyer, 1831	lower Tithonian	Germany.
Suchodus	Valid	Lydekker, 1890	middle Callovian to lower Oxfordian	England and France.
Thalattosuchus	Valid	Young et al., 2020	lower Callovian to lower Oxfordian	England and France.
Torvoneustes^[29]	Valid	Andrade et al., 2010	Kimmeridgian to Tithonian	England.
Tyrannoneustes	Valid	Young et al., 2013	Callovian	England.

See also

• List of marine reptiles

External links

• Web site: Crocodilia: Crocodyliformes (Gobiosuchids, Teleosaurs & Metriorhynchids). Palaeos. https://web.archive.org/web/20230217000801/http://palaeos.com/vertebrates/crocodilia/crocodyliformes.html#Metriorhynchidae. 2023-02-17. live.

Notes and References

1. 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 . 10.1016/j.cretres.2015.07.001 . 2318/1537833 . free .
2. Fitzinger LJFJ. 1843. Systema Reptilium. Wien: Braumüller et Seidel, 106 pp.
3. Mark T. Young . Marco Brandalise de Andrade . 2009 . What is Geosaurus? Redescription of Geosaurus giganteus (Thalattosuchia: Metriorhynchidae) from the Upper Jurassic of Bayern, Germany . Zoological Journal of the Linnean Society . 157 . 3 . 551–585 . 10.1111/j.1096-3642.2009.00536.x . free .
4. Mark T. Young . Stephen L. Brusatte . Marcello Ruta . Marco Brandalise de Andrade . 2010 . The evolution of Metriorhynchoidea (Mesoeucrocodylia, Thalattosuchia): an integrated approach using geometrics morphometrics, analysis of disparity and biomechanics . Zoological Journal of the Linnean Society . 4 . 158 . 801–859 . 10.1111/j.1096-3642.2009.00571.x . free .
5. Fraas E . 1902 . Die Meer-Krocodilier (Thalattosuchia) des oberen Jura unter specieller Berücksichtigung von Dacosaurus und Geosaurus . Palaeontographica . 49 . 1–72 .
6. Spindler. Frederik. Lauer. René. Tischlinger. Helmut. Mäuser. Matthias. 2021-07-05. The integument of pelagic crocodylomorphs (Thalattosuchia: Metriorhynchidae). Palaeontologia Electronica. English. 24. 2. 1–41. 10.26879/1099. 1094-8074. free.
7. Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag,116 pp.
8. Y. . Herrera . M.S. . Fernandez . S.G. . Lamas . L. . Campos . M. . Talevi . Z. . Gasparini . Morphology of the sacral region and reproductive strategies of Metriorhynchidae: a counter-inductive approach . 10.1017/S1755691016000165 . Earth and Environmental Science Transactions of the Royal Society of Edinburgh . 106 . 4 . 247–255 . 2017. free . 11336/66599 . free .
9. Book: 2019. Spindler, Frederik. Live Birth in a Jurassic Marine Crocodile [abstract]. In: Abstracts of the 90th Annual Meeting of the Paläontologische Gesellschaft]. SNSB - BSPG, München. 141. 978-3-946705-07-9. https://web.archive.org/web/20230517045802/https://www.palaeontologie.geowissenschaften.uni-muenchen.de/pdfs/palges2019_abstracts.pdf#page=141. 2023-05-17. live.
10. Book: 2019. Spindler, Frederik. When Bavaria was the Ancient Caribbean – Plattenkalk Fossil Treasures from Painten [abstract]. In: Abstracts of the 90th Annual Meeting of the Paläontologische Gesellschaft]. SNSB - BSPG, München. 10. 978-3-946705-07-9. https://web.archive.org/web/20230517045802/https://www.palaeontologie.geowissenschaften.uni-muenchen.de/pdfs/palges2019_abstracts.pdf#page=10. 2023-05-17. live.
11. Young, M.T.. Sachs, S.. Abel, P.. Foffa, D.. Herrera, Y.. Kitson, J.J.N.. 2020. Convergent evolution and possible constraint in the posterodorsal retraction of the external nares in pelagic crocodylomorphs . Zoological Journal of the Linnean Society . 189. 2. 494–520. 10.1093/zoolinnean/zlaa021. free. 11336/137182. free.
12. Daniel Madzia, Sven Sachs, Mark T. Young, Alexander Lukeneder, Petr Skupien. 2021. Evidence of two lineages of metriorhynchid crocodylomorphs in the Lower Cretaceous of the Czech Republic. Acta Palaeontologica Polonica. 66. 2. 1-11. 10.4202/app.00801.2020. https://web.archive.org/web/20210521113300/https://www.app.pan.pl/archive/published/app66/app008012020.pdf. 2021-05-21. dead.
13. Young MT . 2007 . The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia) . 10.1080/02724634.2007.10010458. Journal of Vertebrate Paleontology . 27 . 3. 170A .
14. Wilkinson LE, Young MT, Benton MJ . 2008 . A new metriorhynchid crocodilian (Mesoeucrocodylia: Thalattosuchia) from the Kimmeridgian (Upper Jurassic) of Wiltshire, UK. . Palaeontology . 51 . 6. 1307–1333 . 10.1111/j.1475-4983.2008.00818.x. free .
15. Gasparini Z, Pol D, Spalletti LA . 2006 . An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia . Science . 311 . 5757. 70–73 . 10.1126/science.1120803. 16282526 . 2006Sci...311...70G . 10312971 . free . 11336/73480 . free .
16. Mueller-Töwe IJ . 2005 . Phylogenetic relationships of the Thalattosuchia . Zitteliana . A45 . 211–213 .
17. Andrea 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 . 10.1016/j.gr.2010.07.007. 2011GondR..19..550C .
18. Mark T. Young . Mark A. Bell . Stephen L. Brusatte . 2011 . Craniofacial form and function in Metriorhynchidae (Crocodylomorpha: Thalattosuchia): modelling phenotypic evolution with maximum-likelihood methods . Biology Letters . 7 . 6 . 913–916 . 10.1098/rsbl.2011.0357 . 21543396 . 3210659.
19. Young, M.T., Brignon, A., Sachs, S., Hornung J.J., Foffa, D., Kitson, J.J.N., Johnson, M.M., Steel, L.. November 2020. Zoological Journal of the Linnean Society. 192. 2. 10.1093/zoolinnean/zlaa092.
20. Stéphane Hua. May 2020. A new specimen of Teleidosaurus calvadosii (Eudes-Deslongchamps, 1866) (Crocodylia, Thalattosuchia) from the Middle Jurassic of France. Annales de Paléontologie. 106. 4. 10.1016/j.annpal.2020.102423.
21. Buffetaut E . 1982 . Radiation évolutive, paléoécologie et biogéographie des Crocodiliens mésosuchienes . Mémoires de la Société Géologique de France . 142 . 1–88 .
22. 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 .
23. Fanti . Federico . Cau . Andrea . Negri . Alessandra . 2014-05-01 . A giant mosasaur (Reptilia, Squamata) with an unusually twisted dentition from the Argille Scagliose Complex (late Campanian) of Northern Italy . Cretaceous Research . en . 49 . 91–104 . 10.1016/j.cretres.2014.01.003 . 0195-6671.
24. Quenstedt FA. 1856. Sonst und Jetzt: Populäre Vortäge über Geologie. Tübingen: Laupp, 131.
25. Koken E . 1883 . Die reptilian der norddeutschen unteren Kreide . Zeitschrift der Deutschen Geologischen Gesellschaft . 35 . 735–827 .
26. Sachs S, Young MT, Hornung JJ . 2020 . The enigma of Enaliosuchus, and a reassessment of the Lower Cretaceous fossil record of Metriorhynchidae . Cretaceous Research . 114 . 104479 . 10.1016/j.cretres.2020.104479 . 20.500.11820/c52d1d56-1bf3-4aae-b2e1-38c85eed44fa . 218996914 . free .
27. 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
28. Young Mark T., Brusatte Stephen L., Ruta M., Andrade Marco B. . 2009 . The evolution of Metriorhynchoidea (Mesoeucrocodylia, Thalattosuchia): an integrated approach using geometrics morphometrics, analysis of disparity and biomechanics . Zoological Journal of the Linnean Society . 158 . 4. 801–859 . 10.1111/j.1096-3642.2009.00571.x. free .
29. 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 . 10.1080/02724634.2010.501442. 83985855 . 11336/69039 . free .