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Cricosaurus is an extinct genus of marine crocodyliforms of the Late Jurassic. belonging to the family Metriorhynchidae. The genus was established by Johann Andreas Wagner in 1858 for three skulls from the Tithonian (Late Jurassic) of Germany. The name Cricosaurus means "Ring lizard", and is derived from the Ancient Greek Krikos- ("ring") and σαῦρος]] - sauros ("lizard"). It was a relatively small reptile, with C. suevicus and C. araucanensis measuring and in total body length, respectively.
Several other species have since been named, including C. suevicus by Fraas in 1901 (originally as a species of Geosaurus).Fraas E. 1901. Die Meerkrokodile (Thalattosuchia n. g.) eine neue Sauriergruppe der Juraformation. Jahreshefte des Vereins für vaterländische Naturkunde, Württemberg 57: 409-418. One former species, C. medius (named by Wagner in 1858) has since been reclassified as a junior synonym of Rhacheosaurus. Fossil specimens referrable to Cricosaurus are known from Late Jurassic deposits in England, France, Switzerland, Germany, Argentina (Vaca Muerta),Gasparini ZB, Dellapé D. 1976. Un nuevo cocodrilo marino (Thalattosuchia, Metriorhynchidae) de la Formación Vaca Muerta (Jurasico, Tithoniano) de la Provincia de Neuquén (República Argentina). Congreso Geológico Chileno 1: c1-c21. Cuba (Jagua Formation), and Mexico (La Caja
Cladogram after Young et al. (2020).
Cladogram after Sachs et al. (2021):Sven Sachs, Mark Thomas Young, Pascal Abel, Heinrich Mallison (2021). A new species of Cricosaurus (Thalattosuchia, Metriorhynchidae) based upon a remarkably well-preserved skeleton from the Upper Jurassic of Germany. Palaeontologia Electronica, 24.2.a24.
From the Nusplingen Plattenkalk (early Tithonian) of southern Germany, both C. suevicus and Dakosaurus maximus are contemporaneous. As with Solnhofen, C. suevicus feed upon fish, while D. maximus was the top predator.Dietl G, Dietl O, Schweigert G, Hugger R. 2000. Der Nusplinger Plattenkalk (Weißer Jura zeta) - Grabungskampagne 1999.
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and Pimienta Formations).Frey, E., Buchy, M.-C., Stinnesbeck, W. & López-Oliva, J.G. 2002. Geosaurus vignaudi n. sp. (Crocodylia, Thalattosuchia), first evidence of metriorhynchid crocodilians in the Late Jurassic (Tithonian) of central-east Mexico (State of Puebla). Canadian Journal of Earth Sciences 39: 1467–1483. and from the earliest Cretaceous (lower Berriasian) of Argentina. C. schroederi from Valanginian of Germany is later reclassified to Enalioetes.
Classification
The original three skulls (all assigned to different species) were poorly known, and the genus had been considered a junior synonym of Metriorhynchus, Geosaurus or Dakosaurus by different palaeontologists in the past.Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag, 116 pp. Some phylogenetic analysis did not support the monophyly of Cricosaurus,Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology 27 (3): 170A. However, a more comprehensive analysis in 2009 showed that the species contained in Cricosaurus were valid, and furthermore that several long-snouted species formerly classified in the related genera Geosaurus, Enaliosuchus and Metriorhynchus were in fact more closely related to the original specimens of Cricosaurus, and thus were re-classified into this genus.Young, M.T. and de Andrade, M.B. (2009). "What is Geosaurus? Redescription of Geosaurus giganteus (Thalattosuchia: Metriorhynchidae) from the Upper Jurassic of Bayern, Germany." Zoological Journal of the Linnean Society, 157: 551-585.
Paleobiology
All currently known species would have been three metres or less in length. When compared to living crocodilians, Cricosaurus can be considered moderate to small-sized. Its body was streamlined for greater hydrodynamic efficiency, which along with its finned tail made it a more efficient swimmer than modern crocodilian species.Massare JA. 1988. Swimming capabilities of Mesozoic marine reptiles; implications for method of predation. Paleobiology 14 (2):187-205.
Salt glands
Recent examination of the fossil specimens of Cricosaurus araucanensis have shown that both juveniles and adults of this species had well-developed . This means that it would have been able to "drink" salt-water from birth (necessary for a pelagic animal) and eat prey that have the same ionic concentration as the surrounding sea water (i.e. ) without dehydration.Fernández M, Gasparini Z. 2000. Salt glands in a Tithonian metriorhynchid crocodyliform and their physiological significance. Lethaia 33: 269-276.Fernández M, Gasparini Z. 2008. Salt glands in the Jurassic metriorhynchid Geosaurus: implications for the evolution of osmoregulation in Mesozoic crocodyliforms. Naturwissenschaften 95: 79-84. Adult specimens of Metriorhynchus also have these well-developed salt glands.Gandola R, Buffetaut E, Monaghan N, Dyke G. 2006. Salt glands in the fossil crocodile Metriorhynchus. Journal of Vertebrate Paleontology 26 (4): 1009-1010.
Niche partitioning
Several species of metriorhynchids are known from the Mörnsheim Formation (Solnhofen limestone, early Tithonian) of Bavaria, Germany: Cricosaurus suevicus, Dakosaurus maximus, Geosaurus giganteus and Rhacheosaurus gracilis. It has been hypothesised that niche partitioning enabled several species of crocodyliforms to co-exist. The top predators of this Formation appear to be D. maximus and G. giganteus, which were large, short-snouted species with serrated teeth. The long-snouted C. suevicus and R. gracilis would have fed mostly on fish, although the more lightly built Rhacheosaurus may have specialised towards feeding on small prey. In addition to these four species of metriorhynchids, a moderate-sized species of Steneosaurus was also contemporaneous.Andrade MB, Young MT. 2008. High diversity of thalattosuchian crocodylians and the niche partition in the Solnhofen Sea . The 56th Symposium of Vertebrate Palaeontology and Comparative Anatomy
Possible viviparity
The hip of Cricosaurus araucanensis contains several features that create an unusually large pelvic opening. The acetabulum, or femur articulation on the hip, is placed very far towards of the bottom of the body relative to the vertebral column, and the sacral ribs are angled downwards at 45°, further increasing the distance between the vertebral column and the pubis-ischium. The hip was effectively a vertical ellipse in cross-section, being tall and wide. In other pseudosuchians like Steneosaurus, Machimosaurus, and Pelagosaurus, the sacral ribs are less angled and more horizontal; in this way, Cricosaurus is actually more similar to aquatic reptiles like Chaohusaurus, Utatsusaurus, and Keichousaurus, the latter of which live birth has been suggested for. In an evaluation of different reproductive hypotheses for Cricosaurus and other metriorhynchids, Herrera et al. considered viviparity more likely than oviparity.
External links
Categories: Thalattosuchia, Prehistoric Pseudosuchian Genera, Oxfordian Genus First Appearances, Kimmeridgian Genera, Tithonian Genera, Valanginian Genus Extinctions, Prehistoric Marine Crocodylomorphs, Late Jurassic Crocodylomorphs Of Europe, Fossils Of France, Jurassic Germany, Fossils Of Germany, Solnhofen Fauna, Late Jurassic Crocodylomorphs Of North America, Jurassic Cuba, Fossils Of Cuba, Jurassic Mexico, Fossils Of Mexico, Late Jurassic Crocodylomorphs Of South America, Jurassic Argentina, Fossils Of Argentina, Neuquén Basin, Fossil Taxa Described In 1858, Taxa Named By Johann Andreas Wagner, Early Cretaceous Crocodylomorphs Of Europe, Early Cretaceous Crocodylomorphs Of South America, Berriasian Genera, Cretaceous Argentina, Cretaceous Germany, Jurassic France
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