Sarcosuchus

Sarcosuchus (/ˌsɑːrkoʊˈsuːkəs/; meaning "flesh crocodile") is an extinct genus of crocodyliform and distant relative of living crocodylians that lived 112 million years ago. It dates from the early Cretaceous Period of what is now Africa and South America and is one of the largest crocodile-like reptiles that ever lived. It was almost twice as long as the modern saltwater crocodile and weighed up to 8 tonnes (7.9 long tons; 8.8 short tons).

The first remains were discovered during several expeditions led by the French paleontologist Albert-Félix de Lapparent, spanning from 1946 to 1959, in the Sahara. These remains were fragments of the skull, vertebrae, teeth, and scutes. In 1964, an almost complete skull was found in Niger by the French CEA, but it was not until 1997 and 2000 that most of its anatomy became known to science, when an expedition led by the American paleontologist Paul Sereno discovered six new specimens, including one with about half the skeleton intact and most of the spine.

Sarcosuchus
Temporal range: Aptian-Albian
~112 Ma
Museum of Natural History Sarcosuchus
S. imperator, Muséum national d'histoire naturelle, Paris
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Family: Pholidosauridae
Genus: Sarcosuchus
Broin & Taquet 1966
Type species
Sarcosuchus imperator
Broin & Taquet 1966
Species
  • S. imperator Broin & Taquet 1966
  • S. hartti Marsh 1869 (originally Crocodylus)

Description

Sarcosuchus Illustration
Life restoration of Sarcosuchus imperator

Sarcosuchus was a giant relative of crocodiles, with fully grown individuals estimated to have reached up to 11–12 m (36–39 ft) in total length and 8 tonnes (8.8 short tons) in weight.[1] It had somewhat telescoped eyes and a long snout comprising 75% of the length of the skull. There were 35 teeth in each side of the upper jaw, while in the lower jaw there were 31 teeth in each side. The upper jaw was also noticeably longer than the lower one leaving a gap between them when the jaws were shut, creating an overbite. In young individuals the shape of the snout resembled that of the living gharial but in fully grown individuals it became considerably broader.[1][2]

Bulla

At the end of its snout, Sarcosuchus presented an expansion, known as a bulla, which has been compared to the ghara seen in gharials. However, unlike the ghara, which is only found in male gharial, the bulla is present in all Sarcosuchus skulls that have been found so far, suggesting that it was not a sexually dimorphic trait. The purpose of this structure remains enigmatic.

Osteoderms

Sarcosuchus scutes
Scutes of S. imperator

The osteoderms, also known as dermal scutes, of Sarcosuchus were similar to those goniopholodids like Sunosuchus and Goniopholis; they formed an uninterrupted surface that started in the posterior part of the neck up to the middle of the tail like is seen in Araripesuchus and other basal crocodyliforms, different from the pattern seen in living crocodiles, which present discontinuity between the osteoderms of the neck and body.[1]

Size

Large crocodyliformes
Size of S. imperator (blue) compared to other crocodyliforms

A common method to estimate the size of crocodiles and crocodile-like reptiles is the use of the length of the skull measured in the midline from the tip of the snout to the back of the skull table,[1] since in living crocodilians there is a strong correlation between skull length and total body length in subadult and adult individuals irrespective of their sex,[3] this method is preferred for Sarcosuchus due to the absence of a complete enough skeleton.

Two regression equations were used to estimate the size of S. imperator, they were created based on measurements gathered from 17 captive gharial individuals from northern India and from 28 wild saltwater crocodile individuals from northern Australia,[1] both datasets supplemented by available measurements of individuals over 1.5 m (4.92 ft) in length found in the literature.[1][4] The largest known skull of S. imperator (the type specimen) is 1.6 m (5.25 ft) long, and it was estimated that the individual it belonged to had a total body length of 11.65 m (38.2 ft),[1] its snout-vent length of 5.7 m (18.7 ft) was estimated using linear equations for the saltwater crocodile[5] and in turn this measurement was used to estimate its body weight at 8 tonnes (8.8 short tons).[1] This shows that Sarcosuchus was able to reach a maximum body size not only greater than previously estimated[1] but also greater than that of the Miocene Rhamphosuchus,[6] the Late Cretaceous Deinosuchus[7][8] and the Miocene Purussaurus.[9]

Classification

Super croc
Reconstructed S. imperator skeleton from behind at the Indianapolis Children's Museum

Sarcosuchus is commonly classified as part of the clade Pholidosauridae,[1][10][11] a group of crocodile-like reptiles (Crocodyliformes) related but outside Crocodylia (the clade containing living crocodiles, alligators and gharials).[1] Within this group it is most closely related to the North American genus Terminonaris.[1] Most members of Pholidosauridae had long, slender snouts and they all were aquatic, inhabiting several different environments, some forms are interpreted as marine, capable of tolerating saltwater while others, like Sarcosuchus, were freshwater forms, the most primitive members of the clade, however, were found in coastal settings, zones of mixing of freshwater and marine waters.[11] Sarcosuchus stands out among pholidosaurids for being considered a generalist predator, different from most known members of the clade which were specialized piscivores.[1]

Simplified cladogram after Fortier et al. (2011).[11]

Pholidosauridae 

Pholidosaurus

Terminonaris

Sarcosuchus

Discovery and naming

Early findings

Sarcosuchus imperator side
Specimen of S. imperator prior to restoration

During the course of several expeditions on the Sahara from 1946 to 1959, led by the French paleontologist Albert-Félix de Lapparent, several fossils of a crocodyliform of large size were unearthed in the region known as the Continental Intercalaire Formation, some of them were found in Foggara Ben Draou, in Mali and near the town of Aoulef, Algeria (informally named as the Aoulef Crocodile) while others came from the Ain el Guettar Formation of Gara Kamboute, in the south of Tunisia, the fossils found were fragments of the skull, teeth, scutes and vertebrae. In 1957, in the region now known as the Elrhaz Formation in the north of Niger several isolated teeth of great size were found by H. Faure. The study of this material by French paleontologist France De Broin helped identify them as coming from a new long snouted crocodile.[10]

Later, in 1964, the research team of the French CEA discovered an almost complete skull in region of Gadoufaoua, in the north of Niger, said skull was shipped to Paris for study and became the holotype of the then new genus and species Sarcosuchus imperator in 1966. The genus name comes from the Greek σάρξ (sarx) meaning flesh and σοῦχος (souchus) meaning crocodile.[10]

Fossils from Brazil

In 1977, a new species of Sarcosuchus was named, S. hartti, from remains found in the late 19th century in the Recôncavo Basin of Brazil.[2] In 1867, American naturalist Charles Hartt found two isolated teeth and sent them to the American paleontologist O. C. Marsh who erected a new species of Crocodylus for them, C. hartti,[12] this material, along with other remains were assigned in 1907 to the genus Goniopholis as G. hartti.[13] Now residing in the British Museum of Natural History the fragment of the lower jaw, dorsal scute and two teeth compromising the species G. hartti were reexamined and conclusively placed in the genus Sarcosuchus.[2]

Recent findings

Sarcosuchus imperator teeth
S. imperator teeth

The next major findings occurred during the expeditions led by the American paleontologist Paul Sereno in 1995 (Aoufous Formation, Morocco), 1997 and the follow-up trip in 2000. Partial skeletons, numerous skulls and 20 tons of assorted other fossils were recovered from the deposits of the Elrhaz Formation, which has been dated as late Aptian or early Albian stages of the Late Cretaceous. It took about a year to prepare the Sarcosuchus remains.[1][14]

Fossils were found in 2010 in the Ifezouane Formation of Morocco. Fossil teeth from the area of Nalut in northwestern Libya, possibly Hauterivian to Barremian in age, might be referable to S. imperator.[15]

Paleobiology

Growth pattern

Sereno took thin sections from trunk osteoderms of an estimated subadult individual (~80% of estimated maximum adult size).[1] Approximately 40 lines of arrested growth (LAG) were counted in these thin sections, suggesting that S. imperator took 50 to 60 years to reach adult size.[1] Given that extant wild crocodylians rarely reach these advanced ages,[3][16] Sereno suggested that S. imperator achieved its large size by extending its period of rapid, juvenile, growth.[1] A similar growth strategy has been suggested for the equally titanic crocodylian Deinosuchus, based on similar criteria.[7]

Diet

Sarcosuchus skull
Reconstructed S. imperator skull

Based on the broader snout of fully grown S. imperator when compared to the living gharial and other narrow-snouted crocodiles, along with a lack of interlocking of the smooth and sturdy-crowned teeth when the jaws were closed, Sereno et al.[1] hypothesized that S. imperator had a generalized diet similar to that of the Nile crocodile, which would have included large terrestrial prey such as the abundant dinosaurs that lived in the same region.[1]

However, a 2014 analysis of a biomechanical model of its skull suggested that unlike Deinosuchus, Sarcosuchus may not have been able to perform the "death roll" maneuver used by extant crocodylians to dismember their prey.[17][18] This suggests that if S. imperator did hunt big game, it probably did not dismember prey in the same fashion as extant crocodylians.

Habitat

The remains of S. imperator were found in a region of the Ténéré Desert named Gadoufaoua, more specifically in the Elrhaz Formation of the Tegama Group, dating from the late Aptian to the early Albian of the Early Cretaceous,[19] approximately 112 million years ago.[1] The stratigraphy of the region and the aquatic fauna that was found therein indicates that it was an inland fluvial environment, entirely freshwater in nature with a humid tropical climate.[1][10][19] S. imperator shared the waters with the holostean fish Lepidotus and the coelacanth Mawsonia.[2] The dinosaur fauna was represented by the iguanodontian Lurdusaurus, which was the most common dinosaur in the region, and its relative Ouranosaurus; there were also two sauropods, Nigersaurus and a currently unnamed sauropod while the theropod fauna included the spinosaurid Suchomimus, the carcharodontosaurid Eocarcharia and the abelisaurid Kryptops.[19][20]

Meanwhile, S. hartti was found in the Recôncavo Basin of Brazil, specifically in the Ilhas Formation of the Bahia series, it was a shallow lacustrine environment dating from the late Aptian, similar in age to the habitat of S. imperator, with similar aquatic fauna, including Lepidotus and two species of Mawsonia. The dinosaur fauna is of a very fragmentary nature and identification does not go beyond indeterminate theropod and iguanodontid remains.[2]

References

  1. ^ a b c d e f g h i j k l m n o p q r s t u Sereno, Paul C.; Larson, Hans C. E.; Sidor, Christian A.; Gado, Boubé (2001). "The Giant Crocodyliform Sarcosuchus from the Cretaceous of Africa". Science. 294 (5546): 1516–9. Bibcode:2001Sci...294.1516S. doi:10.1126/science.1066521. PMID 11679634.
  2. ^ a b c d e Buffetaut, E.; Taquet, P. (1977). "The Giant Crocodilian Sarcosuchus in the Early Cretaceous of Brazil and Niger" (PDF). Palaeontology. 20 (1).
  3. ^ a b Woodward, A. R.; White, J. H.; Linda, S. B. (1995). "Maximum size of the alligator (Alligator mississippiensis)". J. Herpetol. 29 (4).
  4. ^ Wemuth, H. (1964). "Das Verhaltnis zwischen Kopf-, Rumpf- und Schwanzlange bei den rezenten Krokodilen". Senckenbergiana Biologica (in German). 45.
  5. ^ Webb, G. J. W.; Messel, Harry (1978). "Morphometric Analysis of C. porosus from the North Coast of Arnhem Land, Northern Australia". Australian Journal of Zoology. 26: 1. doi:10.1071/zo9780001.
  6. ^ Head, J. J. (2001). "Systematics and body size of the gigantic, enigmatic crocodyloid Rhamphosuchus crassidens, and the faunal history of Siwalik Group (Miocene) crocodylians". Journal of Vertebrate Paleontology. 21 (Supplement to No. 3): 1–117. doi:10.1080/02724634.2001.10010852.
  7. ^ a b Erickson, G. M.; Brochu, C. A. (1999). "How the "terror crocodile" grew so big". Nature. 398 (6724): 205. Bibcode:1999Natur.398..205E. doi:10.1038/18343.
  8. ^ Farlow; et al. (2005). "Femoral dimensions and body size of Alligator mississippiensis: estimating the size of extinct mesoeucrocodylians". Journal of Vertebrate Paleontology. 25 (2): 354–369. doi:10.1671/0272-4634(2005)025[0354:FDABSO]2.0.CO;2.
  9. ^ Jorge Moreno-Bernal (2007). "Size and Palaeoecology of Giant Miocene South American Crocodiles (Archosauria: Crocodylia)". Journal of Vertebrate Paleontology. 27 (3 [suppl.]): 1–182. doi:10.1080/02724634.2007.10010458.
  10. ^ a b c d De Broin, France; Taquet, Philippe (1966). "Découverte d'un Crocodilien nouveau dans le Crétacé inférieur du Sahara". C. R. Acad. Sci. Paris (in French). 262 (D).
  11. ^ a b c Fortier, Daniel; Perea, Daniel; Schultz, Cesar (2011). "Redescription and phylogenetic relationships of Meridiosaurus vallisparadisi, a pholidosaurid from the Late Jurassic of Uruguay". Zoological Journal of the Linnean Society. 163 (Supplement S1): S257. doi:10.1111/j.1096-3642.2011.00722.x.
  12. ^ Marsh, Othniel C. (1869). "Notice of some new reptilian remains from the Cretaceous of Brazil". American Journal of Science. 47 (141).
  13. ^ Mawson, J.; Woodward A. S. (1907). "On the Cretaceous formation of Bahia (Brazil) and on vertebrae fossils collected therein". Q. J. Geol. Soc. Lond. 63.
  14. ^ "Niger Expedition 2000". Project Exploration: The SuperCroc Website. Archived from the original on June 13, 2011. Retrieved 22 March 2013.
  15. ^ Le Loeuff, J.; Métais, E.; Dutheil, D.B.; Rubino, J.L.; Buffetaut, E.; Lafont, F.; Cavin, L.; Moreau, F.; Tong, H.; Blanpied, C.; Sbeta, A. (2010). "An Early Cretaceous vertebrate assemblage from the Cabao Formation of NW Libya" (PDF). Geological Magazine. 147 (5): 750. Bibcode:2010GeoM..147..750L. doi:10.1017/S0016756810000178.
  16. ^ Grenard, S. (1991). Handbook of Alligators and Crocodiles. Malabar, Florida: Kreiger.
  17. ^ Choi, C. Q. (2014-05-04). "Spinning Slayers: Giant Crocs Used 'Death Rolls' to Kill Dinosaurs". LiveScience.com. Purch. Archived from the original on 2014-05-06. Retrieved 2014-05-06.
  18. ^ Blanco, R. E.; Jones, W. W.; Villamil, J. N. (2014-04-16). "The 'death roll' of giant fossil crocodyliforms (Crocodylomorpha: Neosuchia): Allometric and skull strength analysis". Historical Biology. 27 (5): 514–524. doi:10.1080/08912963.2014.893300.
  19. ^ a b c Sereno, Paul C.; Wilson, Jeffrey A.; Witmer, Lawrence M.; Whitlock, John A.; Maga, Abdoulaye; Ide, Oumarou; Rowe, Timothy A. (2007). "Structural Extremes in a Cretaceous Dinosaur". PLoS ONE. 2 (11): e1230. Bibcode:2007PLoSO...2.1230S. doi:10.1371/journal.pone.0001230. PMC 2077925. PMID 18030355.
  20. ^ Sereno, Paul. C.; Brusatte, Stephen L. (2008). "Basal abelisaurid and carcharodontosaurid theropods from the Lower Cretaceous Elrhaz Formation of Niger". Acta Palaeontologica Polonica. 53 (1).

Bibliography

  • Sloan, C. (2002). SuperCroc and the Origin of Crocodiles. National Geographic. ISBN 978-0-7922-6691-4.

Further viewing

  • National Geographic Special on SuperCroc. National Geographic Channel, December, 2001.

External links

Acherontisuchus

Acherontisuchus is an extinct genus of dyrosaurid neosuchian from Middle to Late Paleocene deposits of Colombia. The only known species is A. guajiraensis, whose name means "Acheron crocodile of the Guajira Peninsula".

Aegyptosuchidae

Aegyptosuchidae is an extinct family of eusuchian crocodyliforms from the Cretaceous period of Africa. They are characterized by their large size and flat heads. The family includes two genera, Aegyptosuchus and Aegisuchus.

Albert-Félix de Lapparent

Albert-Félix de Lapparent (1905–1975) was a French palaeontologist. He was also a Sulpician priest. He undertook a number of fossil-hunting explorations in the Sahara desert. He contributed greatly to our knowledge of dinosaurs and other prehistoric creatures. In 1986, José Bonaparte named the dinosaur Lapparentosaurus in his honour.

Dinosaurs named by Lapparent were Inosaurus tedreftensis (Lapparent, 1960) and Lusitanosaurus liassicus (Lapparent and Zbyszewski, 1957).

New species of known genera are also credited to him. In alphabetical order, they are: Apatosaurus alenquerensis (Lapparent and Zbyszewski, 1957), Astrodon pusillus (Lapparent and Zbyszewski, 1957), Brachiosaurus atalaiensis (Lapparent and Zbyszewski, 1957), Brachiosaurus nougaredi (Lapparent, 1960), Cetiosaurus mogrebiensis (Lapparent, 1955), Elaphrosaurus gautieri (Lapparent, 1960), Elaphrosaurus iguidiensis (Lapparent, 1960), Megalosaurus pombali (Lapparent and Zbyszewski, 1957) and Rebbachisaurus tamesnensis (Lapparent, 1960).

The giant crocodile Sarcosuchus was also discovered by him, in 1964.

Amphicotylus

Amphicotylus is an extinct genus of goniopholidid mesoeucrocodylian from the Tithonian of Colorado and Oklahoma.

Coelosuchus

Coelosuchus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils have been found from the Graneros Shale of the Benton Group in Wyoming, and are of Cenomanian age. It was slightly over 1 meter in length.

Dyrosauridae

Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Late Cretaceous (Maastrichtian) to the Eocene. Dyrosaurid fossils are globally distributed, having been found in Africa, Asia, Europe, North America and South America. Over a dozen species are currently known, varying greatly in overall size and cranial shape. All were presumably aquatic, with species inhabiting both freshwater and marine environments. Ocean-dwelling dyrosaurids were among the few marine reptiles to survive the Cretaceous–Paleogene extinction event.

Elosuchus

Elosuchus is an extinct genus of neosuchian crocodyliform that lived during the Middle Cretaceous of what is now North Africa (Morocco and Algeria).

Eusuchia

The Eusuchia ("true crocodiles") are a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades died out 35 and 11 million years ago, all living crocodilian species are eusuchians, as are many extinct forms.

Gallery of Paleontology and Comparative Anatomy

The Gallery of Paleontology and Comparative Anatomy (in French, galerie de Paléontologie et d'Anatomie comparée) is a part of the French National Museum of Natural History (Muséum national d'histoire naturelle, MNHN). It is situated in the Jardin des plantes in Paris near the Gare d'Austerlitz.

The Gallery of Comparative Anatomy (occupying the ground floor), holds nearly a thousand skeletons and interprets their organization and classification. The Gallery of Paleontology (occupying the first and second floor) presents a famous collection of fossil vertebrates, fossil invertebrates and fossil plants. Among the most appreciated pieces by the public is worth mentioning a series of dinosaur skeleton casts (Diplodocus, Iguanodon, Allosaurus, Carnotaurus, Tarbosaurus, Unenlagia, Dromaeosaurus, Bambiraptor) but also a Tyrannosaurus skull (cast of specimen AMNH 5027), an authentic skull of Triceratops, an authentic Compsognathus skeleton, and some authentic fossilised skeletons of other extinct animals like Sarcosuchus, Cynthiacetus, Mammuthus meridionalis, Mammuthus primigenius, Megatherium, Thalassocnus, Ursus spelaeus, Panthera leo spelaea, Aepyornis and many others.

Khoratosuchus

Khoratosuchus is an extinct genus of neosuchian crocodylomorph which existed in northeast Thailand during the early Cretaceous period. Its type species is Khoratosuchus jintasakuli. Khoratosuchus is the youngest and most advanced Mesozoic crocodyliform yet known from Thailand. It possesses several distinctive features that help determine its phylogenetic position among crocodylomorphs, including secondary choanae relatively posterior and almost encircled by the pterygoid bones on the palate and a smooth dorsal surface of the skull.

Mesosuchia

"Mesosuchia" is an obsolete name for a group of terrestrial, semi-aquatic, or fully aquatic crocodylomorph reptiles. The marine crocodile Metriorhynchus had paddle-like forelimbs, Dakosaurus andiniensis had a skull that was adapted to eat large sea reptiles, and Shamosuchus was adapted for eating molluscs and gastropods. Shamosuchus also looked like modern crocodiles and was very closely related to their direct ancestor.

The "Mesosuchia" were formerly placed at Suborder rank as within Crocodylia. The "first" crocodiles were placed within their own suborder, Protosuchia; whilst extant species where placed within Suborder Eusuchia (meaning 'true crocodiles'). Mesosuchia were the crocodylians "in between". As it is a paraphyletic group however, it is not considered valid anymore. It is replaced by its phylogenetic equivalent Mesoeucrocodylia, which contains the taxa herein, the Crocodylia, and some allied forms more recently discovered.

The "Mesosuchia" was composed as:

Family Hsisosuchidae

Family Gobiosuchidae

Infraorder Notosuchia

Family Notosuchidae

Family Sebecidae

Family Baurusuchidae

Infraorder Neosuchia

Family Trematochampsidae

Family Peirosauridae

Genus Lomasuchus

Genus Montealtosuchus

Family Elosuchidae

Family Atoposauridae

Family Dyrosauridae

Family Pholidosauridae

Genus Sarcosuchus

Infraorder Thalattosuchia - Sea "Crocodiles"

Family Teleosauridae

Family Metriorhynchidae

Genus Dakosaurus

Family Goniopholididae

Family Paralligatoridae

Genus Shamosuchus

Nannosuchus

Nannosuchus (meaning "dwarf crocodile") is an extinct genus of goniopholidid mesoeucrocodylian from the Berriasian of England.

Neosuchia

Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to Crocodylus niloticus (the Nile Crocodile) than to Notosuchus terrestris. Neosuchia is very diverse and may be polyphyletic, as the clade has undergone many revisions since it was first named in 1988. Neosuchians first appear in the Early Jurassic with the earliest known goniopholid Calsoyasuchus, which lived during the Sinemurian and Pliensbachian stages.

Paul Sereno

Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites in Inner Mongolia, Argentina, Morocco and Niger. One of his most widely publicized discoveries is that of a nearly complete specimen of Sarcosuchus imperator — popularly known as SuperCroc — at Gadoufaoua in the Tenere desert of Niger.

Pholidosauridae

Pholidosauridae is an extinct family of aquatic neosuchian mesoeucrocodylian crocodylomorphs. Fossils have been found in Europe (Denmark, England, France, Germany, Spain and Sweden), Africa (Algeria, Niger, Mali, Morocco and Tunisia), North America (Canada and the United States) and South America (Brazil and Uruguay). The pholidosaurids first appeared in the fossil record during the Bathonian stage of the Middle Jurassic and became extinct during the Late Turonian stage of the Late Cretaceous.Sarcosuchus is one of the best known pholidosaurs. It is believed to have attained lengths of up to 12 metres (39 ft 4 in) and weighed up to 8 tonnes (7.9 long tons; 8.8 short tons). One genus, Suchosaurus, once thought to be a pholidosaur, has since been shown to be a spinosaurid theropod dinosaur.

Pholidosaurus

Pholidosaurus is an extinct genus of neosuchian crocodylomorph. It is the type genus of the family Pholidosauridae. Fossils have been found in northwestern Germany. The genus is known to have existed during the Berriasian stage of the Early Cretaceous. Fossil material found from the Annero and Jydegård Formations in Skåne, Sweden and on the island of Bornholm, Denmark, have been referred to as a mesoeucrocodylian, and possibly represent the genus Pholidosaurus.

Symptosuchus

Symptosuchus is an extinct genus of goniopholidid mesoeucrocodylian. It is known from the Late Cretaceous of Argentina. Argentine paleontologist Florentino Ameghino named the genus in 1899, along with the type species S. contortidens. It was formally described by Carlos Rusconi in 1934.

Tethysuchia

Tethysuchia is an extinct clade of neosuchian mesoeucrocodylian crocodylomorphs from the late Middle Jurassic (Bathonian stage) to the Early Eocene (Ypresian stage) of Asia, Europe, North America and South America. It was named by the French paleontologist Eric Buffetaut in 1982 as a suborder. Tethysuchia was considered to be a synonym of Dyrosauridae or Pholidosauridae for many years. In most phylogenetic analyses the node Dyrosauridae+Pholidosauridae was strongly supported. De Andrade et al. (2011) suggested that Tethysuchia be resurrected for that node. They defined it as a node-based taxon "composed of Pholidosaurus purbeckensis (Mansel-Pleydell, 1888) and Dyrosaurus phosphaticus (Thomas, 1893), their common ancestor and all its descendants". In their analysis they found that the support for Tethysuchia is actually stronger than the support for Thalattosuchia. The following cladogram shows the position of Tethysuchia among the Neosuchia sensu this study.

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