Metriorhynchus

Metriorhynchus Temporal range: 167–155 Ma PreЄ Є O S D C P T J K Pg N Callovian - Kimmeridgian
Metriorhynchus superciliosus at the Muséum national d'Histoire naturelle, Paris
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
(unranked):	Mesoeucrocodylia
Suborder:	Thalattosuchia
Family:	Metriorhynchidae
Genus:	Metriorhynchus von Meyer, 1830 [1]
Species
M. geoffroyii von Meyer, 1832 (type) [2] M. hastifer (Eudes-Deslongchamps, 1867) M. superciliosus (Blainville, 1853)

Metriorhynchus is an extinct genus of marine crocodyliform that lived in the oceans during the Middle to Late Jurassic. Metriorhynchus was named by the German palaeontologist Christian von Meyer in 1830.^[1] Metriorhynchus was a carnivore that spent much, if not all, its life out at sea. No Metriorhynchus eggs or nests have been discovered, so little is known of the reptile's lifecycle, unlike other large marine reptiles of the Mesozoic, such as plesiosaurs or ichthyosaurs which are known to give birth to live young out at sea. Where Metriorhynchus mated, whether on land or at sea, is currently unknown. The name Metriorhynchus means "Moderate snout", and is derived from the Greek Metrio- ("moderate") and -rhynchos ("snout").

Discovery and species

Fossil specimens referrable to Metriorhynchus are known from Middle-Late Jurassic deposits of England, France and Germany.^[3]

Valid species

Species in this genus are traditionally classed into two skull groups: longirostrine (long, narrow jaws) and brevirostrine (short, broad jaws). However there has been some contention as to how many of these species are valid, especially those from the Callovian.

• Eudes-Deslongchamps (1867–69) found there to be four Callovian species: M. superciliosus, M. moreli, M. blainvillei, and M. brachyrhynchus.^[4]
• Andrews (1913) considered there to be seven valid species: M. superciliosus, M. moreli, M. brachyrhynchus, M. durobrivensis, M. cultridens, M. leedsi and M. laeve.^[5]
• Adams-Tresman (1987) using linear morphometrics however could only distinguish between the two skull groups, so she found there to be two species: M. superciliosus and M. brachyrhynchus.^[6]
• Vignaud (1997) however, considered there to be three Callovian species: M. superciliosus, M. brachyrhynchus and M. leedsi.^[7]

Longirostrine

Metriorhynchus superciliosus

Specimen formerly assigned to M. jaekeli

• M. superciliosus: Western Europe (England, France and Germany) of the Middle-Late Jurassic (Callovian and Oxfordian); M. moreli, M. blainvillei, and M. jaekeli are junior synonyms.
• M. hastifer: Western Europe (France) of the Late Jurassic (Kimmeridgian)
• M. geoffroyii: (type species) Western Europe (England, France and Switzerland) of the Late Jurassic (Kimmeridgian)^[2]; M. palpebrosus, and M. temporalis are junior synonyms. ^[8]

Two longirsotrine species, M. acutus and M. leedsi have been referred to the genus Gracilineustes.^[8]

Brevirostrine

• All brevirostrine species have been transferred to the genera: Purranisaurus and Suchodus.^[8]

Unnamed species

Fragmentary remains of Metriorhynchus are known from South America during the Bajocian ^[9] and Bathonian (both Middle Jurassic).^[10] However, phylogenetic analysis has shown neither of these species can be referred to Metriorhynchus.^[8][11]

Taxonomy and phylogeny

The genera Purranisaurus and Suchodus have been considered junior synonyms of Metriorhynchus,^[3] Recent phylogenetic analyses however, do not support the monophyly of Metriorhynchus.^[12][13][14] Some of the longirostrine forms, however, do appear to form a natural group.^[12][14][15]

The cladogram presented below follows an analysis by Mark Young and Marco Brandalise de Andrade, published in November 2009.^[11]

Metriorhynchus	unnamed M. superciliosus M. moreli unnamed M. palpebrosus unnamed M. hastifer M. sp.

Cladogram after Cau & Fanti (2010).^[16]

Metriorhynchus	M. superciliosus M. geoffroyii M. hastifer M. sp.

Palaeobiology

Description

Life restoration of a pair of Metriorhynchus superciliosus

Averaging 3 metres (9.8 ft) in length, Metriorhynchus was of a similar size to modern crocodiles. However, it had a streamlined body and a finned tail, making it a more efficient swimmer than modern crocodilian species.^[17]

Salt glands

Recent examination of the fossil specimens of Metriorhynchus superciliosus, have shown that adults of this species had well-developed salt glands.^[18] This means that like Geosaurus it would have been able to "drink" salt-water (necessary for a pelagic animal) and eat prey that have the same ionic concentration as the surrounding sea water (i.e. cephalopods) without dehydrating.^[19]

Diet

Metriorhynchus was a versatile and opportunistic predator, predated upon both the armoured belemnites, fast moving fish and the giant filter feeding fish Leedsichthys. Occasionally it was also capable of capturing flying animals such as the pterosaurs and scavenging on plesiosaur carcasses on the seafloor.^[20]

Palaeoecology

Predators

Even though Metriorhynchus was an effective predator, it was vulnerable to predation from apex predators such as Liopleurodon which could grow in excess of 10 meters in length. Since Metriorhynchus had lost its osteoderms, "Armour scutes", to become more efficient swimmers it would have had little defense against larger marine predators.

In popular culture

Metriorhynchus has featured in the Jurassic episode of the BBC television series Sea Monsters.

A metriorhynchus named Cretaceous was one of the main antagonists in Ice Age: The Meltdown.

See also

Paleontology portal

• List of marine reptiles

References

1. ^ ^{a b} Meyer H Von. 1830. Achte Versammlung der Naturforscher und Aerzte zu Heidelberg im September 1829. Isis von Oken, 1830: 517-519.
2. ^ ^{a b} Meyer H von 1832. Paleologica zur Geschichte der Erde. Franfurt am Main, 560 pp.
3. ^ ^{a b} Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag,116 pp.
4. ^ Eudes-Deslongchamps E. 1867-1869. Notes Paléontologiques. Caen and Paris: 320-392.
5. ^ Andrews CW. 1913. A descriptive catalogue of the marine reptiles of the Oxford Clay, Part Two. London: British Museum (Natural History), 206 pp.
6. ^ Adams-Tresman SM. 1987. The Callovian (Middle Jurassic) marine crocodile Metriorhynchus from Central England. Palaeontology 30 (1): 179-194.
7. ^ Vignaud P. 1997. La morphologie dentaire des Thalattosuchia (Crocodylia, Mesosuchia). Palaeovertebrata 26: 35-59.
8. ^ ^{a b c d} 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: 801-859.
9. ^ Gasparini Z, Vignaud P, Chong G. 2000. The Jurassic Thalattosuchia (Crocodyliformes) of Chile: a paleobiogeographic approach. Bulletin Société Géologique de France 171 (6): 657-664
10. ^ Gasparini Z, Cichowolski M, Lazio DG. 2005. First record of Metriorhynchus (Reptilia: Crocodyliformes) in the Bathonian (Middle Jurassic) of the Eastern Pacific. Journal of Paleontology 79 (4): 801–805.
11. ^ ^{a b} Young, Mark T., and 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: 551-585.
12. ^ ^{a b} Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology 27 (3): 170A.
13. ^ Gasparini Z, Pol D, Spalletti LA. 2006. An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia. Science 311: 70-73.
14. ^ ^{a b} 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.
15. ^ Mueller-Töwe IJ. 2005. Phylogenetic relationships of the Thalattosuchia. Zitteliana A45: 211–213.
16. ^ Andrea Cau; Federico Fanti (2010). "The oldest known metriorhynchid crocodylian from the Middle Jurassic of North-eastern Italy: Neptunidraco ammoniticus gen. et sp. nov.". Gondwana Research in press. doi:10.1016/j.gr.2010.07.007. 
17. ^ Massare JA. 1988. Swimming capabilities of Mesozoic marine reptiles; implications for method of predation. Paleobiology 14 (2):187-205.
18. ^ Gandola R, Buffetaut E, Monaghan N, Dyke G. 2006. Salt glands in the fossil crocodile Metriorhynchus. Journal of Vertebrate Paleontology 26 (4): 1009-1010.
19. ^ Fernández M, Gasparini Z. 2008. Salt glands in the Jurassic metriorhynchid Geosaurus: implications for the evolution of osmoregulation in Mesozoic crocodyliforms. Naturwissenschaften 95: 79-84.
20. ^ Forrest R. 2003. Evidence for scavenging by the marine crocodile Metriorhynchus on the carcass of a plesiosaur. Proceedings of the Geologists’ Association 114: 363-366.

Suggested reading

• Buffetaut E. 1982. Radiation évolutive, paléoécologie et biogéographie des Crocodiliens mésosuchienes. Mémoires Societé Geologique de France 142: 1–88

External links

• Metriorhynchus fact files