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]
^Herrera, Yanina; Gasparini, Zulma; Fernández, Marta S. (2015-02-20). "Purranisaurus potens Rusconi, an enigmatic metriorhynchid from the Late Jurassic–Early Cretaceous of the Neuquén Basin". Journal of Vertebrate Paleontology. 35 (2): e904790. doi:10.1080/02724634.2014.904790. hdl:11336/13737. ISSN0272-4634. S2CID128937976.
^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. doi:10.1016/j.annpal.2022.102539. ISSN0753-3969. S2CID254175334.