''Cricosaurus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of marine crocodyliforms of the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

. belonging to the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Metriorhynchidae Metriorhynchidae is an extinct family of specialized, aquatic metriorhynchoid crocodyliforms from the Middle Jurassic to the Early Cretaceous period (Bajocian to early Aptian) of Europe, North America and South America. The name Metriorhync ...

. The genus was established by

Johann Andreas Wagner Johann Andreas Wagner (21 March 1797 – 17 December 1861) was a German palaeontologist, zoologist and archaeologist who wrote several important works on palaeontology. Career Wagner was a professor at the University of Munich, and curator ...

in 1858 for three skulls from the

Tithonian In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by the K ...

(

) of

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

. The name ''Cricosaurus'' means "Ring lizard", and is derived from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

'- ("ring") and -' ("lizard"). It was a relatively small reptile, with ''C. suevicus'' and ''C. araucanensis'' measuring and in total body length, respectively.

Discovery

''Cricosaurus'' was first named by Wagner in 1858,Wagner A. 1858. Zur Kenntniss der Saurier aus den lithographischen Schiefern. ''Abhandlungen der Mathemat.-Physikalischen Classe der Königlich Bayerischen Akademie der Wissenschaften'' 8: 415-528. as a reclassification of a specimen he had previously described in 1852 ("Stenosaurus" ''elegans'', "Stenosaurus" being a misspelling of ''

Steneosaurus ''Steneosaurus'' (from el, στενός , 'narrow' and el, σαῦρος , 'lizard') is a dubious genus of teleosaurid crocodyliform from the Middle or Late Jurassic (Callovian or early Oxfordian) of France. The genus has been used as a was ...

'').Wagner A. 1852. Neu-aufgefundene Saurier-Überreste aus dem lithographischen Schiefern und dem oberen Jurakalk. ''Abhandlungen der Mathemat.-Physikalischen Classe der Königlich Bayerischen Akademie der Wissenschaften'' 6: 661-710. 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 gracilis ''Rhacheosaurus'' is an extinct genus of marine crocodyliform belonging to the family Metriorhynchidae. The genus was established by Christian Erich Hermann von Meyer in 1831 for skeletal remains from the Tithonian (Late Jurassic) of Germany.Mey ...

''. Fossil specimens referrable to ''Cricosaurus'' are known from Late Jurassic deposits in

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

(

Vaca Muerta The Vaca Muerta Formation, commonly known as Vaca Muerta (Spanish for ''Dead Cow''), is a geologic formation of Late Jurassic to Early Cretaceous age, located in the Neuquén Basin in northern Patagonia, Argentina. It is well known as the host roc ...

),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 Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...

(

Jagua Formation The Jagua Formation is a Late Jurassic (middle to late Oxfordian) geologic formation in the Sierra de los Órganos and Sierra del Rosario mountain ranges in Pinar del Río Province, western Cuba. Plesiosaur, pliosaur, pterosaur,Barrett et al., ...

), and

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

( La Caja and

Pimienta Formation The Pimienta Formation is a geologic formation in Mexico. It preserves fossils dating back to the Tithonian-Berriasian. The formation is considered laterally equivalent to the La Casita Formation. The Metriorhynchid '' Cricosaurus vignaudi'' is k ...

s).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 In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ago) ...

) of Argentina and Valanginian of Germany.

Classification

The original three skulls (all assigned to different species) were poorly known, and the genus had been considered a

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

of ''

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 ...

'', ''

Geosaurus ''Geosaurus'' is an extinct genus of marine crocodyliform within the family Metriorhynchidae, that lived during the Late Jurassic and the Early Cretaceous. ''Geosaurus'' was a carnivore that spent much, if not all, its life out at sea. No ''Geosa ...

'' or ''

Dakosaurus ''Dakosaurus'' is an extinct genus of crocodylomorph within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially (flattened from side to ...

'' by different palaeontologists in the past.Steel R. 1973. ''Crocodylia. Handbuch der Paläoherpetologie, Teil 16''. Stuttgart: Gustav Fischer Verlag, 116 pp. Some

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis did not support the

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

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.

Cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

after Young ''et al.'' (2020). Cricosaurus bambergensis 455445

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. DOI: 10.26879/928

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

salt gland The salt gland is an organ for excreting excess salts. It is found in the cartilaginous fishes subclass elasmobranchii (sharks, rays, and skates), seabirds, and some reptiles. Salt glands can be found in the rectum of sharks. Birds and reptile ...

s. This means that it would have been able to "drink" salt-water from birth (necessary for a

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

animal) and eat prey that have the same ionic concentration as the surrounding sea water (i.e.

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s) without

dehydrating In physiology, dehydration is a lack of total body water, with an accompanying disruption of Metabolism, metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental tempe ...

.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 ''

'' 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 Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total lan ...

, Germany: ''Cricosaurus suevicus'', ''

Dakosaurus maximus ''Dakosaurus'' is an extinct genus of crocodylomorph within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially (flattened from side t ...

'', ''

Geosaurus giganteus ''Geosaurus'' is an extinct genus of marine crocodyliform within the family Metriorhynchidae, that lived during the Late Jurassic and the Early Cretaceous. ''Geosaurus'' was a carnivore that spent much, if not all, its life out at sea. No ''Geo ...

'' and ''

''. It has been hypothesised that

niche partitioning In ecology, niche differentiation (also known as niche segregation, niche separation and niche partitioning) refers to the process by which competing species use the environment differently in a way that helps them to coexist. The competitive excl ...

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 ''

'' 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 From the

Nusplingen Nusplingen is a municipality of the Zollernalbkreis, Zollernalb district of Baden-Württemberg, Germany. History In 1803, Nusplingen became a possession of the Principality of Hohenzollern-Sigmaringen, who traded the town in 1813 to the Kingdom ...

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.

Possible viviparity

The hip of ''Cricosaurus araucanensis'' contains several features that create an unusually large pelvic opening. The

acetabulum The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) that c ...

, or

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

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 ischium () form ...

. The hip was effectively a vertical ellipse in cross-section, being tall and wide. In other pseudosuchians like ''

'', ''

Machimosaurus ''Machimosaurus'' is an extinct genus of machimosaurid crocodyliform from the Late Jurassic (Kimmeridgian and Tithonian) and Early Cretaceous. The type species, ''Machimosaurus hugii'', was found in Switzerland. Other fossils have been found ...

'', and ''

Pelagosaurus ''Pelagosaurus'' (meaning "lizard of the open sea") is an extinct genus of thalattosuchian crocodyliform that lived during the Toarcian stage of the Lower Jurassic, around 183 Ma to 176 Ma (million years ago), in shallow epicontinental seas that ...

'', the sacral ribs are less angled and more horizontal; in this way, ''Cricosaurus'' is actually more similar to aquatic reptiles like ''

Chaohusaurus ''Chaohusaurus'' is an extinct genus of basal ichthyopterygian, depending on definition possibly ichthyosaur, from the Early Triassic of Chaohu and Yuanan, China. Discovery The type species ''Chaohusaurus geishanensis'' was named and des ...

'', ''

Utatsusaurus ''Utatsusaurus hataii'' is the earliest-known ichthyopterygian which lived in the Early Triassic period (c. 245–250 million years ago). It was nearly long with a slender body. The first specimen was found in Utatsu-cho (now part of Minamisan ...

'', and ''

Keichousaurus ''Keichousaurus'' (key-cho-saurus) is a genus of marine reptile in the pachypleurosaur family which went extinct at the close of the Triassic in the Triassic-Jurassic extinction event. The name derives from Kweichow (now Guizhou Province) in Ch ...

'', 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 Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...

more likely than

oviparity Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and m ...

References

External links

When Crocodiles Once Dived Like Dolphins and Whales
NY Times article on marine Thalattosuchian fossils, including Cricosaurus. Published April 20, 2020; Updated June 25, 2020 {{Taxonbar, from=Q147582 Thalattosuchians 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