Metriorhynchus is an extinctgenus 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 GermanpalaeontologistChristian von Meyer in 1832.[2] The name Metriorhynchus means "Moderate snout", and is derived from the GreekMetrio- ("moderate") and -rhynchos ("snout").
Discovery and species
Fossil specimens referrable to Metriorhynchus are known from Kimmeridgian (Late Jurassic) deposits of France.[1]
Valid species
Only one valid species is recognized today, the type species M. geoffroyii (now called M. brevirostris).[1]"Metriorhynchus" hastifer and "M." palpebrosus are generically distinct from the Metriorhynchus type species, with hastifer being recovered as a geosaurine.[3][4] 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.[5][6]Metriorhynchus superciliosus was also shown to be generically distinct from the type species, M. brevirostris, and now has its own genus Thalattosuchus.[1]
Life reconstruction of Metriorhynchus brevirostris
The genera Purranisaurus and Suchodus have been considered junior synonyms of Metriorhynchus.[7] Recent phylogenetic analyses however, do not support the monophyly of Metriorhynchus, as believed during the 1860s-2010.[8][9][10][1]
Eudes-Deslongchamps (1867–69) recognized four Callovian species of Metriorhynchus: M. superciliosus, M. moreli, M. blainvillei, and M. brachyrhynchus.[11] 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.[12] 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.[13] Vignaud (1997) however, considered there to be three Callovian species: M. superciliosus, M. brachyrhynchus and M. leedsi,[14] and a 2022 study describing a new metriorhynchid specimen advocated returning to this taxonomic system, considering Gracilineustes and Thalattosuchus junior synonyms of Metriorhynchus.[15]
Unnamed species
Fragmentary remains attributed to Metriorhynchus are known from South America during the Bajocian[16] and Bathonian (both Middle Jurassic).[17] However, phylogenetic analysis has shown that these species cannot be referred to Metriorhynchus.[5][18][1]
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.[19] Metriorhynchids also had a hip anatomy conducive for live birth and evidence from the genus Dakosaurus does show that they did this..[20]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.[1] It was 3 meters (9.8 feet).[21]
Paleoecology
Metriorhynchus was a carnivore, one fossil shows it having eaten the gill apparatus of giant fish known as Leedsichthys. The idea of Metriorhynchus attacking weak Leedsichthys individuals has been speculated of having been the case in the past such as in the BBC and Discovery Channel documentary, Sea Monsters.[22][23]
^Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag,116 pp.
^Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology27 (3): 170A.
^Eudes-Deslongchamps E. 1867-1869. Notes Paléontologiques. Caen and Paris: 320-392.
^Andrews CW. 1913. A descriptive catalogue of the marine reptiles of the Oxford Clay, Part Two. London: British Museum (Natural History), 206 pp.
^Adams-Tresman SM. 1987. The Callovian (Middle Jurassic) marine crocodile Metriorhynchus from Central England. Palaeontology30 (1): 179-194.
^Vignaud P. (1997). La morphologie dentaire des Thalattosuchia (Crocodylia, Mesosuchia). Palaeovertebrata26: 35-59.
^Le Mort, Jonas; Martin, Jeremy E.; Picot, Laurent; Hua, Stéphane (2022-07-01). "First description of the most complete Metriorhynchus aff. superciliosus (Thalattosuchia) specimen from the Callovian of the Vaches-Noires cliffs (Normandy, France) and limitations in the classification of Metriorhynchidae". Annales de Paléontologie. 108 (3): 102539. Bibcode:2022AnPal.10802539L. doi:10.1016/j.annpal.2022.102539. ISSN0753-3969. S2CID254175334.
.jpg){kind=small}
