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.[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.

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. All brevirostrine species have been transferred to the genera: Purranisaurus and Suchodus.
 * Eudes-Deslongchamps (1867–69) found there to be four Callovian species: M. superciliosus, M. moreli, M. blainvillei, and M. brachyrhynchus.[5]
 * Andrews (1913) considered there to be seven valid species: M. superciliosus, M. moreli, M. brachyrhynchus, M. durobrivensis, M. cultridens, M. leedsi and M. laeve.[6]
 * 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.[7]
 * Vignaud (1997) however, considered there to be three Callovian species: M. superciliosus, M. brachyrhynchus and M. leedsi.
 * 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.[4]

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

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.

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.

Cladogram after Cau & Fanti (2010).