Rauisuchian
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"Rauisuchia" is a
paraphyletic group Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In con ...
of mostly large and carnivorous
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
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. Rauisuchians are a category of archosaurs within a larger group called
Pseudosuchia Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
, which encompasses all archosaurs more closely related to
crocodilia Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...
ns than to birds and other
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. First named in the 1940s, Rauisuchia was a name exclusive to Triassic archosaurs which were generally large (often ), carnivorous, and quadrupedal with a pillar-erect hip posture, though exceptions exist for all of these traits. Rauisuchians, as a traditional
taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...
group, were considered distinct from other Triassic archosaur groups such as early dinosaurs,
phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...
s (crocodile-like carnivores),
aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...
s (armored herbivores), and
crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably more ...
(lightly-built crocodilian ancestors). However, more recent studies on archosaur evolution have upended this idea based on
phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...
and
cladistics Cladistics ( ; from Ancient Greek 'branch') is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesiz ...
, a modern approach to taxonomy based on
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 ...
s (nested
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
groups of common ancestry). Since the early 2010s, archosaur classification schemes have stabilized on a system where Rauisuchia is rendered an
evolutionary grade A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Phylogenetics The concept of evolutionary grades ...
, or even a
wastebin taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...
.
Crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably more ...
most likely originated from a rauisuchian ancestor based on a myriad of shared traits, and some "rauisuchians" (such as ''
Postosuchus ''Postosuchus'', meaning "Crocodile from Post", is an extinct genus of rauisuchid reptiles comprising two species, ''P. kirkpatricki'' and ''P. alisonae'', that lived in what is now North America during the Late Triassic. ''Postosuchus'' is a ...
'' and ''
Rauisuchus ''Rauisuchus'' (meaning "Wilhelm Rau's crocodile") is a genus of extinct archosaurs which lived in what is now the Geopark of Paleorrota (Santa María Formation), Brazil, during the Triassic, Late Triassic period (235–228 million years ago). It ...
'') appear to be more closely related to crocodylomorphs than to other "rauisuchians" (such as ''
Prestosuchus ''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 ...
'' and ''
Saurosuchus ''Saurosuchus'' (meaning "lizard crocodile") is an extinct genus of large loricatan pseudosuchian archosaurs that lived in South America during the Late Triassic period. It was a heavy, ground-dwelling, quadrupedal carnivore, likely being the a ...
''). As a result, Rauisuchia in its traditional usage may be considered
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
: a group which is defined by shared ancestry but also excludes a descendant taxon (in this case, crocodylomorphs). To designate it as an informal group in scientific literature, the name is often enclosed in quotation marks. Several
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
groups have been erected to classify "rauisuchians" in a cladistic framework. The closest concept is the clade
Paracrocodylomorpha Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomor ...
, which includes most "rauisuchian" taxa and their crocodylomorph descendants. Paracrocodylomorpha is divided into two branches:
Poposauroidea Poposauroidea is a clade of advanced Pseudosuchian, pseudosuchians. It includes poposaurids, Shuvosaurinae, shuvosaurids, ctenosauriscids, and other unusual pseudosuchians such as ''Qianosuchus'' and ''Lotosaurus''. It excludes most large predato ...
, which includes a variety of strange "rauisuchians" (some of which were bipedal and/or herbivorous) and
Loricata Loricata is a clade of archosaur reptiles that includes crocodilians and some of their Triassic relatives, such as ''Postosuchus'' and ''Prestosuchus''. More specifically, Loricata includes Crocodylomorpha (the persistent archosaur subset which ...
, which includes most typical "rauisuchians" and crocodylomorphs.


Characteristics

"Rauisuchians" had an erect gait with their legs oriented vertically beneath the body rather than sprawling outward. This type of gait is also seen in dinosaurs, but evolved independently in the two groups. In dinosaurs, the hip socket faces outward and the
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
(thigh bone) connects to the side of the hip; while in rauisuchians, the hip socket faces downward to form a shelf of bone under which the femur connects. This has been referred to as the pillar-erect posture. "Rauisuchians" lived throughout most of the Triassic. The group died out in the late Triassic, before the Triassic-Jurassic extinction event (barring crocodylomorphs, which survive to the present in the form of crocodilians). After their extinction,
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
dinosaurs were able to emerge as the sole large terrestrial predators, though there is still some debate over how the extinction influenced dinosaur evolution. The footprints of meat-eating dinosaurs may have suddenly increased in size at the start of the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
, when rauisuchians were absent. However, the apparent increase in dinosaur footprint size has instead been argued to be a result of increasing abundance of large theropods, rather than an abrupt acquisition of large size. Some "rauisuchians" may have existed in the very early Jurassic based on bone fragments from South Africa, but this identification is tentative. The name "Rauisuchia" comes from the genus ''
Rauisuchus ''Rauisuchus'' (meaning "Wilhelm Rau's crocodile") is a genus of extinct archosaurs which lived in what is now the Geopark of Paleorrota (Santa María Formation), Brazil, during the Triassic, Late Triassic period (235–228 million years ago). It ...
'', which was named after fossil collector Dr. Wilhelm Rau. The name ''Rauisuchus'' means Wilhelm Rau's crocodile.


History of classification

"Rauisuchians" were originally thought to be related to
erythrosuchids Erythrosuchidae (meaning "red crocodiles" in Greek) are a family of large basal archosauriform carnivores that lived from the later Early Triassic (Olenekian) to the early Middle Triassic (Anisian). Naming The family Erythrosuchidae was named by ...
, but it is now known that they are
pseudosuchia Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
ns. Three families have historically been recognised:
Prestosuchidae Prestosuchidae (in its widest usage) is a polyphyletic grouping of carnivorous archosaurs that lived during the Triassic. They were large active terrestrial apex predators, ranging from around in length. They succeeded the Erythrosuchidae as th ...
,
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 ...
, and
Poposauridae Poposauridae is a family of large carnivorous archosaurs which lived alongside dinosaurs during the Late Triassic. They were around long. Poposaurids are known from fossil remains from North and South America. While originally believed to be ...
, as well as a number of forms (e.g. those from the
Olenekian In the geologic timescale, the Olenekian is an age (geology), age in the Early Triassic epoch (geology), epoch; in chronostratigraphy, it is a stage (stratigraphy), stage in the Lower Triassic series (stratigraphy), series. It spans the time betw ...
of Russia) that are too primitive and/or poorly known to fit in any of these groups. There has been considerable suggestion that the group as currently defined is
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
, representing a number of related lineages independently evolving and filling the same ecological niche of medium to top terrestrial predator. For example, Parrish (1993) and Juul (1994) considered poposaurid rauisuchians to be more closely related to
Crocodilia Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...
than to prestosuchids. Nesbitt (2003) presented a different phylogeny with a
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
Rauisuchia. The group may even be something of a "
wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...
". Determining exact phylogenetic relationships is difficult because of the scrappy nature of a lot of the material. However, further discoveries and studies, such as a study on the braincase of ''
Batrachotomus ''Batrachotomus'' is a genus of prehistoric archosaur. Fossils of this animal have been found in southern Germany and dated from the Ladinian stage of the Middle Triassic period, around 242 to 237 million years ago. ''Batrachotomus'' was descri ...
'' (2002) and restudies of other forms, such as ''
Erpetosuchus ''Erpetosuchus'' is an extinct genus of pseudosuchian from the Late Triassic. The type species of ''Erpetosuchus'' is ''E. granti''. It was first described by E. T. Newton in 1894 for remains found in northeastern Scotland, including four specim ...
'' (2002) have shed some light on the evolutionary relationships of this poorly known group.


Cladistics

Despite its inclusion as an informal grouping in numerous
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
studies, "Rauisuchia" has never received a formal definition. Most analyses in the past decade have found "Rauisuchia" to be a paraphyletic grouping, including all studies with a large sample size. Those that found the possibility that it was a natural group produced only weak support for this hypothesis. In his large 2011 analysis of archosaurian relationships, Nesbitt recommended that the term "Rauisuchia" be abandoned. In a study of the
ctenosauriscid Ctenosauriscidae is an extinct family of pseudosuchian archosaurs within the clade Poposauroidea. Ctenosauriscids existed in Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 mill ...
''
Arizonasaurus ''Arizonasaurus'' (meaning "Arizona reptile") was a ctenosauriscid archosaur from the Middle Triassic (243 million years ago) Moenkopi Formation of what is now Arizona. The taxon is known for having a large back sail formed by elongated neural sp ...
'', paleontologist
Sterling Nesbitt Sterling Nesbitt (born March 25, 1982, in Mesa, Arizona) is an American paleontologist best known for his work on the origin and early evolutionary patterns of archosaurs. He is currently an associate professor at Virginia Tech in the Departme ...
defined 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 ...
of rauisuchians called "Group X". This group includes ''Arizonasuchus'', ''
Lotosaurus ''Lotosaurus'' is an extinct genus of sail-backed poposauroid known from Hunan Province of central China. Discovery ''Lotosaurus'' is known from the holotype IVPP V 4881 (or possibly V 4880), an articulated and well-preserved s ...
'', ''
Sillosuchus ''Sillosuchus'' is a genus of shuvosaurid poposauroid archosaur that lived in South America during the Late Triassic period. Shuvosaurids were an unusual family of reptiles belonging to the group Poposauroidea; although their closest modern relati ...
'', ''
Shuvosaurus ''Shuvosaurus'' (meaning "Shuvo hatterjees lizard") is a genus of beaked, bipedal poposauroid pseudosuchian from the Late Triassic (early to middle Norian) of western Texas. Despite superficially resembling a Theropoda, theropod dinosaur, es ...
'', and ''
Effigia ''Effigia'' is an extinct genus of shuvosaurid known from the Late Triassic of New Mexico, south-western USA. With a bipedal stance, long neck, and a toothless beaked skull, ''Effigia'' and other shuvosaurids bore a resemblance to the ornithomimi ...
''. One distinguishing feature of Group X is their lack of osteoderms, which are common among many other
crurotarsan Crurotarsi is a clade of archosauriformes, archosauriform reptiles that includes crocodilians and stem-crocodilians and possibly bird-line Archosaur, archosaurs too if the extinct, crocodile-like phytosaurs are more distantly related to crocodile ...
s. Many more features are found in the
pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...
, including fully fused
sacral vertebrae The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...
and a long, thin crest on the ilium called the supra- acetabular crest. Additionally, many members of Group X have smooth frontal and
nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...
s, which make up the upper portion of the
rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...
. In other "rauisuchians" and many other crurotarsans, this area has bumps and ridges. "Group X" is now termed
Poposauroidea Poposauroidea is a clade of advanced Pseudosuchian, pseudosuchians. It includes poposaurids, Shuvosaurinae, shuvosaurids, ctenosauriscids, and other unusual pseudosuchians such as ''Qianosuchus'' and ''Lotosaurus''. It excludes most large predato ...
. Nesbitt later erected another clade, "Group Y", in 2007. Group Y falls within Group X to include ''Sillosuchus'', ''Shuvosaurus'', and ''Effigia''. Group Y is diagnosed by the presence of four or more sacral vertebrae with fully fused
neural arch Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
es, which is also seen in
theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...
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 (a case of
evolutionary convergence Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
). In addition, the cervical vertebrae that make up the
neck The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Addition ...
are strongly amphicoelus, meaning that they are concave at both ends. The
fourth trochanter The fourth trochanter is a shared characteristic common to archosaurs. It is a protrusion on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the '' musculus caudofemoralis longus'', the m ...
, a ridge of
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
on the
femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...
for muscle attachment seen in nearly all archosaurs, is absent in Group Y. "Group Y" is now termed
Shuvosauridae Shuvosauridae is an extinct family of theropod-like pseudosuchians within the clade Poposauroidea. Shuvosaurids existed in North America (United States) and South America (Argentina) during the Late Triassic period (late Carnian to Rhaetian stage ...
. Although not placed within Group Y, ''Lotosaurus'' shares many similarities with members of the clade, foremost of which is
edentulous Toothlessness or edentulism is the condition of having no teeth. In organisms that naturally have teeth, it is the result of tooth loss. Organisms that never possessed teeth can also be described as edentulous. Examples are the members of the fo ...
, or toothless, jaws. Edentulism is also seen in ''Shuvosaurus'' and ''Effigia'', which have beak-like jaws. Nesbitt suggested that the derived characters of ''Lotosaurus'' may indicate that it is a
transitional form A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross ...
between basal members of Group X and members of Group Y. Below is the
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
from Nesbitt (2007): In their phylogenetic study of archosaurs, Brusatte ''et al.'' (2010) found only weak support for Rauisuchia as a monophyletic grouping. As a result of their analysis, two clades were found to be within Rauisuchia, which they named Rauisuchoidea and Poposauroidea. Rauisuchoidea included Rauisuchidae and Prestosuchidae, as well as several basal taxa that were once assigned to the families, including ''
Fasolasuchus ''Fasolasuchus'' is an extinct genus of loricatan. Fossils have been found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina that date back to the Norian stage of the Late Triassic, making it one o ...
'' and ''
Ticinosuchus ''Ticinosuchus'' is an extinct genus of suchian archosaur from the Middle Triassic (Anisian– Ladinian) of Switzerland and Italy. Description One of only a handful of fossil reptiles that have been found in Switzerland, ''Ticinosuchus'' (mea ...
''. Poposauroidea included poposaurids and ctenosauriscids, but the phylogeny had a large
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...
of genera in both groups that was difficult to resolve, which included ''Arizonasaurus'', ''
Poposaurus ''Poposaurus'' is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern and eastern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, bea ...
'', and ''Sillosuchus''. However, the characters linking these two groups were weak, and the question as to whether or not "Rauisuchia" forms a natural group remains unresolved. Brusatte et al. (2010) was one of the last studies to find a monophyletic Rauisuchia clade. Below is the cladogram from Brusatte ''et al.'' (2010): In a more thorough test of archosaurian relationships published in 2011 by Sterling Nesbitt, "rauisuchians" were found to be paraphyletic, with
Poposauroidea Poposauroidea is a clade of advanced Pseudosuchian, pseudosuchians. It includes poposaurids, Shuvosaurinae, shuvosaurids, ctenosauriscids, and other unusual pseudosuchians such as ''Qianosuchus'' and ''Lotosaurus''. It excludes most large predato ...
at the base of the clade
Paracrocodylomorpha Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomor ...
, and the rest of the "rauisuchians" forming a grade within the clade
Loricata Loricata is a clade of archosaur reptiles that includes crocodilians and some of their Triassic relatives, such as ''Postosuchus'' and ''Prestosuchus''. More specifically, Loricata includes Crocodylomorpha (the persistent archosaur subset which ...
. Nesbitt noted that no previous study of "rauisuchian" relationships had ever included a wide variety of supposed "rauisuchians" as well as a large number of non-"rauisuchian" taxa as controls.


Fossil record

Well-known "rauisuchians" include ''
Ticinosuchus ''Ticinosuchus'' is an extinct genus of suchian archosaur from the Middle Triassic (Anisian– Ladinian) of Switzerland and Italy. Description One of only a handful of fossil reptiles that have been found in Switzerland, ''Ticinosuchus'' (mea ...
'' of the Middle Triassic of Switzerland and Northern Italy, ''
Saurosuchus ''Saurosuchus'' (meaning "lizard crocodile") is an extinct genus of large loricatan pseudosuchian archosaurs that lived in South America during the Late Triassic period. It was a heavy, ground-dwelling, quadrupedal carnivore, likely being the a ...
'' of the Late Triassic (late
Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...
) of Argentina, ''
Prestosuchus ''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 ...
'' of the Middle-Late Triassic (late Ladinian-early Carnian) of Brazil, and ''
Postosuchus ''Postosuchus'', meaning "Crocodile from Post", is an extinct genus of rauisuchid reptiles comprising two species, ''P. kirkpatricki'' and ''P. alisonae'', that lived in what is now North America during the Late Triassic. ''Postosuchus'' is a ...
'' of the Late Triassic (
Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...
) of the southwest United States. The first "rauisuchian" known to paleontology was ''
Teratosaurus ''Teratosaurus'' is a genus of rauisuchians known from the Triassic Stubensandstein ( Löwenstein Formation - Norian stage) of Germany. It is estimated to be 6.2 meters (20.35 ft) long. Discovery In 1860, Sixt Friedrich Jakob von Kapff ...
'', a German genus from the Late Triassic (Norian) of Germany. However, ''Teratosaurus'' was considered an early theropod dinosaur for much of its history,See for example Colbert, E.H., 1961, ''Dinosaurs: Their Discovery and Their World'', Dutton, New York, 1961 p.67 before it was demonstrated to be non-dinosaurian in the 1980s. The concept of "rauisuchians" as a distinct group of reptiles distantly related to crocodiles was recognized by discoveries in Brazil in the 1940s (particularly ''Prestosuchus'' and ''
Rauisuchus ''Rauisuchus'' (meaning "Wilhelm Rau's crocodile") is a genus of extinct archosaurs which lived in what is now the Geopark of Paleorrota (Santa María Formation), Brazil, during the Triassic, Late Triassic period (235–228 million years ago). It ...
'') and emphasized further by the description of ''Ticinosuchus'' in the 1960s. The oldest known "rauisuchians", in terms of geological age, are probably from the end of the
Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.9 Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which ...
(late
Olenekian In the geologic timescale, the Olenekian is an age (geology), age in the Early Triassic epoch (geology), epoch; in chronostratigraphy, it is a stage (stratigraphy), stage in the Lower Triassic series (stratigraphy), series. It spans the time betw ...
). Most of these early fossils are fragmentary and dubious remains from Russia, but some are better-described and constrained, such as ''
Xilousuchus ''Xilousuchus'' is an extinct genus of poposauroid from lower Triassic (Olenekian stage) deposits of Fugu County of northeastern Shanxi Province, China. Xilousuchus is one of the oldest archosaurs known to date. Discovery and naming It is ...
'', a
ctenosauriscid Ctenosauriscidae is an extinct family of pseudosuchian archosaurs within the clade Poposauroidea. Ctenosauriscids existed in Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 mill ...
from the Heshanggou Formation of China. ''Xilousuchus'' is neither the earliest-branching archosaur nor "rauisuchian" despite its early age, and its presence in the Early Triassic suggests that other archosaur fossils are simply undiscovered from that time. The last known "rauisuchians", excluding their descendants the crocodylomorphs, are from the latter part of the Late Triassic. The shuvosaurid ''
Effigia ''Effigia'' is an extinct genus of shuvosaurid known from the Late Triassic of New Mexico, south-western USA. With a bipedal stance, long neck, and a toothless beaked skull, ''Effigia'' and other shuvosaurids bore a resemblance to the ornithomimi ...
'', from the "siltstone member" of the
Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In ...
in
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
, may be as young as the
Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...
, the last stage of the Triassic. ''Effigia'' was recovered from the ''Coelophysis'' Quarry of
Ghost Ranch Ghost Ranch is a retreat and education center in Rio Arriba County in north central New Mexico, United States. It is about 65 miles northwest of Santa Fe and 14 miles from Abiquiu, the nearest community. In the later 20th century, it was the ...
.Nesbitt, S. (2007). "The anatomy of ''Effigia okeeffeae'' (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa." ''Bulletin of the American Museum of Natural History'', 302: 84 pp. http://digitallibrary.amnh.org/dspace/handle/2246/5840 The same site also preserves a large undescribed archosaur, CM 73372, which seemingly represents a transitional form between "rauisuchians" and crocodylomorphs. Indeterminate large paracrocodylomorph material from the
Lower Elliot Formation The Elliot Formation is a geological formation and forms part of the Stormberg Group, the uppermost geological Stratigraphic unit, group that comprises the greater Karoo Supergroup. Outcrops of the Elliot Formation have been found in the northern ...
of
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
may be even younger, late Rhaetian or possibly even lowermost Jurassic.


List of rauisuchian genera

The following is a list of valid pseudosuchian genera which have been informally or formally classified as rauisuchians, as well as their modern cladistic interpretation. This list does not include genera named for dubious and poorly-diagnosed "rauisuchian" material from Russia ('' Dongusia'', '' Energosuchus'', ''
Jaikosuchus ''Jaikosuchus'' is an extinct genus of proterosuchid archosauriform. It contains a single species, ''J. magnus''. Fossils have been found from European Russia that date back to the upper Olenekian stage of the Early Triassic. Discovery The gen ...
'', ''
Jushatyria ''Jushatyria'' is an extinct genus of archosaur. Fossils have been found in the Koltaevo III Locality, district of Kumertau near the Ural Mountains in European Russia from the Bukobay Gorizont. The locality dates back to the Ladinian stage of th ...
'', '' Scythosuchus'', ''
Tsylmosuchus ''Tsylmosuchus'' is an extinct genus of proterosuchid archosauriform reptile known from Western Russia. Fossils referred to ''Tsylmosuchus'' occurred over a wide area in sediments corresponding to the Induan and Olenekian stages of the Early ...
'', ''
Vjushkovisaurus ''Vjushkovisaurus'' is an extinct genus of Middle Triassic archosauriform. It is known from the Anisian-aged Donguz Gorizont in Sol-Iletsk, Orenburg Oblast, Russia. The genus was named in 1982, with the type species being ''V. berdjanensis'' ...
,
Vytshegdosuchus ''Vytshegdosuchus'' is an extinct genus of paracrocodylomorph archosaur known from the Early Triassic (latest Olenekian stage) Yarenskian Gorizont of the Komi Republic of the European section of Russia. It contains a single species, ''Vytshegdo ...
'') and China (''
Fenhosuchus ''Fenhosuchus'' is an extinct genus of archosauriform. The holotype, IVPP V 2697, and referred materials have been found in the Hsishihwa locality at Wuhsiang, China, from the Upper Ermaying Formation (also Ehrmaying). The locality dates back ...
'', ''
Wangisuchus ''Wangisuchus'' is an extinct genus of archosauriform reptile from the Middle Triassic of China that is known from fragmentary fossil jaw bones. These bones were found at the Hsishihwa locality in the upper Ermaying Formation, which dates to the ...
''), nor taxa reclassified as non-"rauisuchian" archosaurs (''
Ornithosuchus ''Ornithosuchus'' (from , "bird" and , "crocodile") is an extinct genus of pseudosuchians from the Late Triassic (Carnian) Lossiemouth Sandstone of Scotland. It was originally thought to be the ancestor to the carnosaurian dinosaurs (such as ''Al ...
'', ''
Gracilisuchus ''Gracilisuchus'' (meaning "slender crocodile") is an extinct genus of tiny pseudosuchian (a group which includes the ancestors of crocodilians) from the Late Triassic of Argentina. It contains a single species, ''G. stipanicicorum'', which is pl ...
'', '' Dongusuchus'', ''
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 ...
'').


See also

*


Notes


References

* * * {{Taxonbar, from=Q1069200 Fossil taxa described in 1942 Paraphyletic groups Pseudosuchia Taxa named by Friedrich von Huene