Metriorhynchus

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. 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, Germany, Argentina, and Chile.

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.
 * Andrews (1913) considered there to be seven valid species: M. superciliosus, M. moreli, M. brachyrhynchus, M. durobrivensis, M. cultridens, M. leedsi and M. laeve.
 * 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.
 * Vignaud (1997) however, considered there to be three Callovian species: M. superciliosus, M. brachyrhynchus and M. leedsi.

Longirostrine
 * M. superciliosus: Western Europe (England and France) of the Middle-Late Jurassic (Callovian and Oxfordian); M. moreli, M. blainvillei, and M. jaekeli are junior synonyms.
 * M. leedsi: Western Europe (England) of the Middle Jurassic (Callovian); M. laeve is a junior synonym.
 * M. palpebrosus: Western Europe (England) of the Late Jurassic (Kimmeridgian); M. temporalis is a junior synonym.
 * M. hastifer: Western Europe (France) of the Late Jurassic (Kimmeridgian)
 * M. acutus: Western Europe (France) of the Late Jurassic (Kimmeridgian)
 * M. geoffroyii: (type species) Western Europe (France) of the Late Jurassic (Kimmeridgian)

Brevirostrine
 * M. brachyrhynchus: Western Europe (England and France) of the Middle-Late Jurassic (Callovian and Oxfordian); M. cultridens is a junior synonym.
 * M. durobrivensis: Western Europe (England and France) of the Middle Jurassic (Callovian). Was originally the type species of the genus Suchodus, but it was regarded as a junior synonym of Metriorhynchus by Andrews, 1913.
 * M. casamiquelai: Middle Jurassic of Chile (Callovian);
 * M. westermanni: Middle Jurassic of Chile (Callovian). Although previously considered a junior synonym of M. casamiquelai, it has been revalidated;
 * M. potens: End Jurassic of Argentina (Tithonian). Was originally the type species of the genus Purranisaurus, but it was regarded as a possible junior synonym of Metriorhynchus by Gasparini.

Unnamed species
Fragmentary remains of Metriorhynchus are known from South America during the Bajocian and Bathonian (both Middle Jurassic).

Taxonomy and phylogeny
The genera Purranisaurus and Suchodus are junior synonyms of Metriorhynchus, Recent phylogenetic analyses however, do not support the monophyly of Metriorhynchus. Some of the longirostrine forms, however, do appear to form a natural group.

Description
Averaging 3 meters (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.

Salt glands
Recent examination of the fossil specimens of Metriorhynchus superciliosus, have shown that adults of this species had well-developed salt glands. 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.

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.

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 metres in length. Since Metriorhynchus had lost its osteoderms, "armour scutes", to become more efficient swimmers it would have had little defence against larger marine predators.

Suggested reading

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