Cricosaurus

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 Greek '- ("ring") and -' ("lizard").
Discovery.
"Cricosaurus" was first named by Wagner in 1858, as a reclassification of a specimen he had previously described in 1852 ("Stenosaurus" "elegans", "Stenosaurus" being a misspelling of "Steneosaurus").
Several other species have since been named, including "C. suevicus" by Fraas in 1901 (originally as a species of "Geosaurus"). One former species, "C. medius" (named by Wagner in 1858) has since been reclassified as a junior synonym of "Rhacheosaurus gracilis". Fossil specimens referrable to "Cricosaurus" are known from Late Jurassic deposits in England, France, Switzerland, Germany, Argentina (Vaca Muerta), Cuba (Jagua Formation), and Mexico (La Caja and Pimienta Formations).
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. Some phylogenetic analysis did not support the monophyly of "Cricosaurus", 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.
Cladogram after Young "et al." (2020).
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.
Salt glands.
Recent examination of the fossil specimens of "Cricosaurus araucanensis" have shown that both juveniles and adults of this species had well-developed salt glands. 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. cephalopods) without dehydrating. Adult specimens of "Metriorhynchus" also have these well-developed salt glands.
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.
From the slightly older Nusplingen Plattenkalk (late Kimmeridgian) 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.
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.