# Metriorhynchus

Metriorhynchus is an extinct genus of marine crocodyliform that lived in the oceans during the Late Jurassic. The type species, M. brevirostris was named in 1829 as a species of Steneosaurus before being named as a separate genus by the German palaeontologist Christian von Meyer in 1832. 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 Kimmeridgian (Late Jurassic) deposits of France.

### Valid species

Only one valid species is recognized today, the type species M. geoffroyii (now called M. brevirostris). "Metriorhynchus" hastifer and "M." palpebrosus are generically distinct from the Metriorhynchus type species, with hastifer being recovered as a geosaurine. Species in this genus were traditionally classed into two skull groups: longirostrine (long, narrow jaws) and brevirostrine (short, broad jaws). However, most of brevirostrine species have been transferred to the genera Purranisaurus and Suchodus. Metriorhynchus superciliosus was also shown to be generically distinct from the type species, M. brevirostris, and now has its own genus Thalattosuchus.
The genera Purranisaurus and Suchodus have been considered junior synonyms of Metriorhynchus. Recent phylogenetic analyses however, do not support the monophyly of Metriorhynchus, as believed during the 1860s-2010.
Eudes-Deslongchamps (1867–69) recognized four Callovian species of Metriorhynchus: M. superciliosus, M. moreli, M. blainvillei, and M. brachyrhynchus. Later, Andrews (1913) considered there to be seven valid species: M. superciliosus, M. moreli, M. brachyrhynchus, M. durobrivensis, M. cultridens, M. leedsi and M. laeve. However, Adams-Tresman (1987), using linear morphometrics, could only distinguish between the two skull groups, so she found there to be two species from the Oxford Clay, M. superciliosus and M. brachyrhynchus. Vignaud (1997) however, considered there to be three Callovian species: M. superciliosus, M. brachyrhynchus and M. leedsi, and a 2022 study describing a new metriorhynchid specimen advocated returning to this taxonomic system, considering Gracilineustes and Thalattosuchus junior synonyms of Metriorhynchus.

### Unnamed species

Fragmentary remains attributed to Metriorhynchus are known from South America during the Bajocian and Bathonian (both Middle Jurassic). However, phylogenetic analysis has shown that these species cannot be referred to Metriorhynchus.

## Description

Metriorhynchus was a thalattosuchian, a group of marine crocodylomorphs. It was a member of the Metriorhynchidae, a group of thalattosuchians with a tail anatomy which indicates that they had a tail fluke similar to that of a shark. Unlike many other pseudosuchians, they did not have extensive osteoderms covering the body. Instead it appears that they had smoother skin similar to other marine reptiles like plesiosaurs and ichthyosaurs. Metriorhynchids also had a hip anatomy conducive for live birth and evidence from the genus Dakosaurus does show that they did this.. Metriorhynchus can be distinguished from other metriorhynchids in that the three front teeth get bigger from front to back, with the first being round and the third more oval-shaped. The jaws have a narrow point where different parts of the upper jaw meet, and there are at least 13 teeth before the palatine bones start. The teeth are mostly oval-shaped, but after the third one, they become rounder. The front part of the nasal bones stops near the eighth tooth, and unlike most animals, it has a single large external nostril instead of two separate ones. The opening for the nostrils begins behind the first tooth and ends just past the last one in the front section of the jaw. It was 3 meters (9.8 feet).

## Paleoecology

Metriorhynchus was a carnivore. One fossil shows it has eaten the gill apparatus of a giant fish known as Leedsichthys. The idea of Metriorhynchus attacking weak Leedsichthys individuals has been speculated to be the case in the past such as in the BBC and Discovery Channel documentary Sea Monsters.