''Rauisuchus'' (meaning "Wilhelm Rau's

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include ...

") is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of extinct

archosaur Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...

s which lived in what is now the

Geopark A geopark is a protected area with internationally significant geology within which Sustainability, sustainable development is sought and which includes tourism, conservation, education and research concerning not just geology but other relevant s ...

of Paleorrota (

Santa María Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and other ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, during the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

period (235–228 million years ago). It contains one species, ''R. tiradentes''.''Rauisuchus''
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.orgF. v. Huene. (1942) ''Die fossilen Reptilien des südamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabung in Südbrasilien 1928/29.'' München: C.H. Beck'sche Verlagsbuchhandlung

Discovery and naming

In 1928 or 1929, near the road from Santa Maria to San Jose, Dr. Wilhelm Rau, a German fossil collector working under

Friedrich von Huene Baron Friedrich Richard von Hoyningen-Huene (22 March 1875 – 4 April 1969) was a German nobleman paleontologist who described a large number of dinosaurs, more than anyone else in 20th-century Europe. He studied a range of Permo-Carbonife ...

, discovered the remains of a

rauisuchid Rauisuchidae is a group of large (up to ) predatory Triassic archosaurs. Some disagreement exists over which genera should be included in the Rauisuchidae and which should be in the related Prestosuchidae and Poposauridae, and indeed whether thes ...

crocodile. He made the discovery some from the road at a site known as the Zahnsanga, which was likely a

ravine A ravine is a landform that is narrower than a canyon and is often the product of streambank erosion. Ravines are typically classified as larger in scale than gullies, although smaller than valleys. Ravines may also be called a cleuch, dell, ...

escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. Due to the similarity, the term '' scarp'' may mistakenly be incorrectly used inte ...

parallel to the road. The Zahnsanga site was part of the Alemoa Member of the

Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, " rauisuchian" pseudosuchians, and early dinosaurs and othe ...

and was found in the uppermost of an layer. von Huene then sent the ''R. tiradentes'' material back to Germany alongside other fossils, including the holotype of ''

Prestosuchus chiniquensis ''Prestosuchus'' (meaning "Prestes crocodile") is an extinct genus of pseudosuchian in the group Loricata, which also includes ''Saurosuchus'' and ''Postosuchus''. It has historically been referred to as a "rauisuchian", and was the defining mem ...

''. von Huene (1936) named ''Rauisuchus'' in a list of the

Thecodontia Thecodontia (meaning 'socket-teeth'), now considered an obsolete taxonomic grouping, was formerly used to describe a diverse "order" of early archosaurian reptiles that first appeared in the latest Permian period and flourished until the end of t ...

,v. Huene, F. (1936). The constitution of the Thecodontia. ''American Journal of Science'' 32:207-217 but no diagnosis or description was given, so it remained a ''nomen dubium'' until being properly described by von Huene (1942). Krebs (1973) described the tarsus of ''R. tiradentes'' and the

lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...

was assigned in 1976 and consists of BSPG AS XXV 60–68, 71–100, 105–119 and 121 (the right premaxilla, right postorbital, left squamosal, left jugal, right pterygoid, right nasal, both splenials, left surangular, prearticular and angular, odontoid(?), axis, cervical, dorsal and caudal vertebrae, ribs, chevron bones, right scapulacoracoid, left pubis, right tibia, fibula and astragalus, and body osteoderms).Krebs, B. (1976). Pseudosuchia. In: Kuhn O, ed Handbuch der Paläoherpetologie, Thecodontia. Stuttgart: Gustav Fischer Verlag, 40–98. It is unclear if the lectotype remains belonged to one or two individuals. The specimens found by Rau were eventually re-described by Lautenschlager & Rauhut (2014) and they identified that from Localities 15-17, one or two specimens were found. According to von Huene (1942), 'Find 1025' was assigned to BSPG AS XXV 122 (a partial left maxilla) and 'Find 1020' was assigned to BSPG AS XXV 123 (a cervical vertebra), BSPG AS XXV 124, (a rib fragment), BSPG AS XXV 120 and BSPG, no number (two chevron bone fragments) and BSPG AS XXV 88 (a complete left ilium). Lautenschlager & Rauhut (2014) found that the remains from Locality 15 ('Find 1020') could not be diagnostically assigned to ''Rauisuchus'', and so were removed from the genus. They also noted that von Huene (1942) assigned two more specimens from other localities to ''R. tiradentes'': several isolated teeth, BSPG AS XXV 101 (the proximal end of an ulna) and BSPG AS XXV 102 (a partial metatarsal), but these cannot be confidently assigned to ''R. tiradentes'' as no overlapping material is known.

Description

''Rauisuchus'' possibly grew to a length of and would be high at the hips and it had a weight of around . ''Rauisuchus'' is distinguished from other members of the

Rauisuchidae Rauisuchidae is a group of large (up to ) predatory Triassic archosaurs. Some disagreement exists over which genera should be included in the Rauisuchidae and which should be in the related Prestosuchidae and Poposauridae, and indeed whether the ...

on the basis of a knob-like thickening on the base of the posterior process of the premaxilla, short, ventrally keeled cervicals, lacking postzygodiapophyseal laminae, and elongated caudals with an accessory neural spine and a postspinal lamina.

Classification

''Rauisuchus'' belonged to a group of land-dwelling relatives to

s known as the Rauisuchidae, although it was initially assigned to the

Theriodontia The theriodonts (clade Theriodontia) are a major group of therapsids which appeared during the Middle Permian and which includes the gorgonopsians and the eutheriodonts, itself including the therocephalians and the cynodonts. Naming In 1876, R ...

in 1936. Rauisuchids were among the top predators of their day, eating other reptiles for food and maybe hunting early

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s. It was placed as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to ''

Tikisuchus ''Tikisuchus'' is an extinct genus of rauisuchid archosauromorph. It is known from the Late Triassic Tiki Formation in the Shahdol District of central India and was the first rauisuchid to have been found in Asia. The horizon from which remains ...

'' and ''

Yarasuchus ''Yarasuchus'' (meaning "red crocodile") is an extinct genus of avemetatarsalian archosaur that lived during the Anisian stage of the Middle Triassic of India.Bandyopadhyay, S. and Sengupta, D. P. (1999). Middle Triassic vertebrate faunas from I ...

'', forming a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

with the two.

References

{{Taxonbar, from=Q540139 Rauisuchids Triassic reptiles of South America Triassic Brazil Fossils of Brazil Santa Maria Formation Fossil taxa described in 1936 Taxa named by Friedrich von Huene Prehistoric pseudosuchian genera