| "Rauisuchians" | |
|---|---|
 | |
| Mounted skeleton ofPrestosuchus chiniquensis (a basal loricatan) in theAmerican Museum of Natural History. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Suchia |
| Informal group: | †Rauisuchia Huene, 1942 |
| Groups included | |
| Cladistically included but traditionally excluded taxa | |
"Rauisuchia" is aparaphyletic group of mostly large and carnivorousTriassicarchosaurs.[2] Rauisuchians are a category of archosaurs within a larger group calledPseudosuchia, which encompasses all archosaurs more closely related tocrocodilians than to birds and otherdinosaurs. First named in the 1940s, Rauisuchia was a name exclusive to Triassic archosaurs which were generally large (often 4 to 6 metres (13 to 20 ft)), carnivorous, and quadrupedal with a pillar-erect hip posture, though exceptions exist for all of these traits. Rauisuchians, as a traditionaltaxonomic group, were considered distinct from other Triassic archosaur groups such as early dinosaurs,phytosaurs (crocodile-like carnivores),aetosaurs (armored herbivores), andcrocodylomorphs (lightly-built crocodilian ancestors).[3]
However, more recent studies on archosaur evolution have upended this idea based onphylogenetic analyses andcladistics, a modern approach to taxonomy based onclades (nestedmonophyletic groups of common ancestry). Since the early 2010s, archosaur classification schemes have stabilized on a system where Rauisuchia is rendered anevolutionary grade, or even awastebin taxon.Crocodylomorphs most likely originated from a rauisuchian ancestor based on a myriad of shared traits, and some "rauisuchians" (such asPostosuchus andRauisuchus) appear to be more closely related to crocodylomorphs than to other "rauisuchians" (such asPrestosuchus andSaurosuchus).[2]
As a result, Rauisuchia in its traditional usage may be consideredparaphyletic: 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.[2] Severalmonophyletic groups have been erected to classify "rauisuchians" in a cladistic framework. The closest concept is the cladeParacrocodylomorpha, which includes most "rauisuchian" taxa and their crocodylomorph descendants. Paracrocodylomorpha is divided into two branches:Poposauroidea, which includes a variety of strange "rauisuchians" (some of which were bipedal and/or herbivorous) andLoricata, which includes most typical "rauisuchians" and crocodylomorphs.[2]
"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 thefemur (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.[4][5] This has been referred to as the pillar-erect posture.[6]
"Rauisuchians" lived throughout most of the Triassic. The group died out in the late Triassic, before theTriassic-Jurassic extinction event (barring crocodylomorphs, which survive to the present in the form of crocodilians).[7] After their extinction,theropod 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 theJurassic, when rauisuchians were absent.[8] 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.[9] Some "rauisuchians" may have existed in the very early Jurassic based on bone fragments from South Africa, but this identification is tentative.[1]
The name "Rauisuchia" comes from the genusRauisuchus, which was named after fossil collector Dr.Wilhelm Rau. The nameRauisuchus means Wilhelm Rau's crocodile.
"Rauisuchians" were originally thought to be related toerythrosuchids,[10] but it is now known that they arepseudosuchians.[11][2] Three families have historically been recognised:Prestosuchidae,Rauisuchidae, andPoposauridae, as well as a number of forms (e.g. those from theOlenekian 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 isparaphyletic, representing a number of related lineages independently evolving and filling the same ecological niche of medium to top terrestrial predator. For example, Parrish (1993)[12] and Juul (1994)[13] considered poposaurid rauisuchians to be more closely related toCrocodilia than to prestosuchids. Nesbitt (2003)[14] presented a different phylogeny with amonophyletic Rauisuchia. The group may even be something of a "wastebasket taxon". 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 ofBatrachotomus (2002)[15] and restudies of other forms, such asErpetosuchus (2002)[16] have shed some light on the evolutionary relationships of this poorly known group.
Despite its inclusion as an informal grouping in numerousphylogenetic 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.[17] In his large 2011 analysis of archosaurian relationships, Nesbitt recommended that the term "Rauisuchia" be abandoned.[2]
In a study of thectenosauriscidArizonasaurus, paleontologistSterling Nesbitt defined aclade of rauisuchians called "Group X".[18] This group includesArizonasuchus,Lotosaurus,Sillosuchus,Shuvosaurus, andEffigia. One distinguishing feature of Group X is their lack of osteoderms, which are common among many othercrurotarsans. Many more features are found in thepelvis, including fully fusedsacral vertebrae and a long, thin crest on theilium called the supra-acetabular crest. Additionally, many members of Group X have smoothfrontal andnasal bones, which make up the upper portion of therostrum. In other "rauisuchians" and many other crurotarsans, this area has bumps and ridges.[19] "Group X" is now termedPoposauroidea.[2]
Nesbitt later erected another clade, "Group Y", in 2007.[19] Group Y falls within Group X to includeSillosuchus,Shuvosaurus, andEffigia. Group Y is diagnosed by the presence of four or more sacral vertebrae with fully fusedneural arches, which is also seen intheropoddinosaurs (a case ofevolutionary convergence). In addition, the cervical vertebrae that make up theneck are stronglyamphicoelus, meaning that they are concave at both ends. Thefourth trochanter, a ridge ofbone on thefemur for muscle attachment seen in nearly all archosaurs, is absent in Group Y.[19] "Group Y" is now termedShuvosauridae.[2]
Although not placed within Group Y,Lotosaurus shares many similarities with members of the clade, foremost of which isedentulous, or toothless, jaws. Edentulism is also seen inShuvosaurus andEffigia, which have beak-like jaws. Nesbitt suggested that the derived characters ofLotosaurus may indicate that it is atransitional form between basal members of Group X and members of Group Y.[19]
Below is thecladogram from Nesbitt (2007):[19]
| Rauisuchia | |
In their phylogenetic study of archosaurs, Brusatteet 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, includingFasolasuchus andTicinosuchus. Poposauroidea included poposaurids and ctenosauriscids, but the phylogeny had a largepolytomy of genera in both groups that was difficult to resolve, which includedArizonasaurus,Poposaurus, andSillosuchus. However, the characters linking these two groups were weak, and the question as to whether or not "Rauisuchia" forms a natural group remains unresolved.[17] Brusatte et al. (2010) was one of the last studies to find a monophyletic Rauisuchia clade.
Below is the cladogram from Brusatteet al. (2010):[17]
| Rauisuchia | |
In a more thorough test of archosaurian relationships published in 2011 by Sterling Nesbitt, "rauisuchians" were found to be paraphyletic, withPoposauroidea at the base of the cladeParacrocodylomorpha, and the rest of the "rauisuchians" forming a grade within the cladeLoricata. 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.[2]
Well-known "rauisuchians" includeTicinosuchus of the Middle Triassic of Switzerland and Northern Italy,Saurosuchus of the Late Triassic (lateCarnian) of Argentina,Prestosuchus of the Middle-Late Triassic (late Ladinian-early Carnian) of Brazil, andPostosuchus of the Late Triassic (Norian) of the southwest United States. The first "rauisuchian" known to paleontology wasTeratosaurus, a German genus from the Late Triassic (Norian) of Germany. However,Teratosaurus was considered an earlytheropod dinosaur for much of its history,[20] before it was demonstrated to be non-dinosaurian in the 1980s.[21][22] The concept of "rauisuchians" as a distinct group of reptiles distantly related to crocodiles was recognized by discoveries in Brazil in the 1940s (particularlyPrestosuchus andRauisuchus) and emphasized further by the description ofTicinosuchus in the 1960s.
The oldest known "rauisuchians", in terms of geological age, are probably from the end of theEarly Triassic (lateOlenekian). Most of these early fossils are fragmentary and dubious remains from Russia, but some are better-described and constrained, such asXilousuchus, actenosauriscid from theHeshanggou 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.[23] The last known "rauisuchians", excluding their descendants the crocodylomorphs, are from the latter part of the Late Triassic. The shuvosauridEffigia, from the "siltstone member" of theChinle Formation inNew Mexico, may be as young as theRhaetian, the last stage of the Triassic.Effigia was recovered from theCoelophysis Quarry ofGhost Ranch.[24] The same site also preserves a large undescribed archosaur, CM 73372, which seemingly represents a transitional form between "rauisuchians" and crocodylomorphs.[2] Indeterminate large paracrocodylomorph material from theLower Elliot Formation ofSouth Africa may be even younger, late Rhaetian or possibly even lowermost Jurassic.[1]
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,Jushatyria,Scythosuchus,Tsylmosuchus,Vjushkovisaurus,Vytshegdosuchus) and China (Fenhosuchus,Wangisuchus), nor taxa reclassified as non-"rauisuchian" archosaurs (Ornithosuchus,Gracilisuchus,Dongusuchus,Yarasuchus).
| Genus | Authority | Year | Location | Unit | Age | Traditional classification | Modern classification | Notes | Images |
|---|---|---|---|---|---|---|---|---|---|
| Apatosuchus | Sues & Schoch | 2013 |  Germany | Löwenstein Formation (Stubensandstein) | Norian | Theropoda | Loricata | A small "rauisuchian" based on a partial skull. Originally considered a species ofHalticosaurus, a contemporary theropod dinosaur. | |
| Arganasuchus | Jalil & Peyer | 2007 |  Morocco | Timezgadiouine Formation | Carnian? | Rauisuchidae | Loricata | A "rauisuchian" based on scant skull and postcranial material similar to that ofBatrachotomus,Luperosuchus, andPostosuchus. |  |
| Arizonasaurus | Welles | 1947 |  United States | Moenkopi Formation | Anisian | Theropoda? Rauisuchia? | Poposauroidea (Ctenosauriscidae) | One of the most complete ctenosauriscids, owing to a partial skeleton with skull and hip material discovered in 2002. Vital for understanding the affinities of ctenosauriscids withpoposaurs. |  |
| Batrachotomus | Gower | 1999 | Germany | Erfurt Formation (Lower Keuper) | LateLadinian | Prestosuchidae /Rauisuchidae | Loricata | One of the most completely-known "rauisuchians", with numerous fossils recovered from sites atKupferzell,Crailsheim andVellberg-Eschenau. | |
| Bromsgroveia | Galton | 1985 |  United Kingdom | Bromsgrove Sandstone | Anisian | Theropoda /Temnospondyli /Poposauridae | Poposauroidea (Ctenosauriscidae) | Named based on a distinctivepoposaur-likeilium, but also possibly incorporating "rauisuchian" fossil material such as teeth andvertebrae described fromEngland since the mid-19th century. | |
| Bystrowisuchus | Sennikov | 2012 |  Russia | Lipovskaya Formation (Gamskian Gorizont) | LateOlenekian? | Ctenosauriscidae | Poposauroidea (Ctenosauriscidae) | An early ctenosauriscid with low-spinedcervical (neck) vertebrae similar toXilousuchus. | |
| Ctenosauriscus | Kuhn | 1964 | Germany | Solling Formation | LateOlenekian toAnisian? | "Pelycosauria" /Temnospondyli /Ctenosauriscidae | Poposauroidea (Ctenosauriscidae) | Known from slabs ofsail-backed dorsal vertebrae first discovered in 1871 and originally named as the (preoccupied) genusCtenosaurus in 1902. Its affinities were strongly debated until stabilizing as poposauroid archosaur upon the discovery of newArizonasaurus andLotosaurus fossils. |  |
| Dagasuchus | Lacerdaet al. | 2015 |  Brazil | MiddleSanta Maria Formation (Santacruzodon Assemblage Zone) | LateLadinian or earlyCarnian | N/A | Loricata | A medium-sized "rauisuchian" based on a hip bone which helps to fill a gap in thebiostratigraphic record of Brazilian archosaurs. | |
| Decuriasuchus | França | 2011 | Brazil | LowerSanta Maria Formation (Dinodontosaurus Assemblage Zone) | LateLadinian or earlyCarnian | Prestosuchidae | Loricata | A medium-sized "rauisuchian" named from 10 individuals (including several nearly-complete skeletons) which died and fossilized together, suggesting agregarious social structure. |  |
| Effigia | Nesbitt &Norell | 2006 | United States | Chinle Formation ("siltstone member") | LateNorian orRhaetian | DerivedSuchia | Poposauroidea (Shuvosauridae) | A bizarre pseudosuchian convergent onornithomimids, with a toothless skull, theropod-like hip, and very short arms. Discovered within a sediment block collected from theCoelophysis Quarry ofGhost Ranch,New Mexico. |  |
| Etjosuchus | Tolchardet al. | 2021 |  Namibia | Omingonde Formation | Ladinian or earlyCarnian | Erythrosuchidae | Loricata | A large and possibly bipedal "rauisuchian" based on a partial skeleton previously misattributed to the erythrosuchidErythrosuchus. | |
| Fasolasuchus | Bonaparte | 1981 |  Argentina | Los Colorados Formation | LateNorian | Rauisuchidae | Loricata | One of the last and largest "rauisuchians", occurring alongside an increasingly diverse fauna ofsauropodomorph dinosaurs. |  |
| Heptasuchus | Dawleyet al. | 1979 | United States | Popo Agie Formation | LateCarnian? | Prestosuchidae? | Loricata | One of the oldest predatory archosaurs from North America, based on skull and postcranial fragments fromWyoming. Probably a close relative ofBatrachotomus. |  |
| Hypselorhachis | Butleret al. | 2009 |  Tanzania | Manda Formation | Anisian? toCarnian? | Ctenosauriscidae | Poposauroidea (Ctenosauriscidae) | A ctenosauriscid based on a single well-preserved vertebra with a very long neural spine. First mentioned in an unpublished 1966 byAlan Charig, but not formally described until 2009. |  |
| Lotosaurus | Zhang | 1975 |  China | Badong Formation | Anisian? toCarnian? | "Lotosauridae" | Poposauroidea | An unusual quadruped combining aneural spine sail with a toothless skull. Known from abundant fossils clustered into abonebed, but most of these fossils remain undescribed. |  |
| Luperosuchus | Romer | 1971 | Argentina | Chanares Formation (Tarjadia Assemblage Zone) | LateLadinian or earliestCarnian | Prestosuchidae | Loricata | A medium-sized "rauisuchian" with a skull similar toPrestosuchus andSaurosuchus. |  |
| Mambawakale | Butleret al. | 2022 | Tanzania | Manda Formation | Anisian? toCarnian? | "Pallisteriidae" | BasalParacrocodylomorpha? | A possible paracrocodylomorph based on a massive partial skull. Mentioned as "Pallisteria angustimentum" in an unpublished 1967 manuscript byAlan Charig, but not formally described (and provided a new scientific name) until 2022. |  |
| Mandasuchus | Butleret al. | 2018 | Tanzania | Manda Formation | Anisian? toCarnian? | Prestosuchidae? | BasalParacrocodylomorpha? | One of the most basal loricatans or poposauroids, first mentioned in a 1956 doctoral thesis byAlan Charig but not formally described until 2018. | |
| Polonosuchus | Brusatteet al. | 2009 |  Poland | Krasiejów claypit | LateCarnian? | Rauisuchidae | Loricata (Rauisuchidae) | A large rauisuchid, formerly named as a species ofTeratosaurus and currently considered a close relative ofPostosuchus. |  |
| Poposaurus | Mehl | 1915 | United States | Popo Agie Formation,Dockum Group,Chinle Formation (Monitor Butte Member,Blue Mesa Member,Sonsela Member) | Late Carnian? to middleNorian | Dinosauria /Poposauridae | Poposauroidea (Poposauridae) | A widespread bipedal carnivore with hip bones so similar to dinosaurs that for decades it was mistaken as one. Though skull fragments are very rare, the postcrania is well-described according to a nearly complete skeleton discovered inUtah in 2003. | _flipped.jpg) |
| Postosuchus | Chatterjee | 1985 | United States | Cooper Canyon Formation,Chatham Group?,Chinle Formation? | Norian | Poposauridae /Rauisuchidae | Loricata (Rauisuchidae) | A large rauisuchid with a short skull and possibly bipedal locomotion. One of the most well-described and widespread "rauisuchians" from North America, though not all fossils referred to the genus may actually belong to it. Proposed as an ancestor totyrannosaurids when first described. |  |
| Prestosuchus | Huene | 1942 | Brazil | LowerSanta Maria Formation (Dinodontosaurus Assemblage Zone) | LateLadinian or earlyCarnian | Prestosuchidae | Loricata (Prestosuchidae) | Among the largest and most well-described "rauisuchians", a quadrupedal form based on multiple partial skeletons. One massive well-preserved skull has been named under the dubious genus "Karamuru vorax". |  |
| Procerosuchus | Huene | 1938 | Brazil | LowerSanta Maria Formation (Dinodontosaurus Assemblage Zone) | LateLadinian or earlyCarnian | Prestosuchidae | Loricata (Prestosuchidae?) | A poorly-known taxon, possibly a synonym or species ofPrestosuchus. | |
| Qianosuchus | Li et al. | 2006 | China | Guanling Formation (Panxian biota) | Anisian | IndeterminateCrurotarsi | Poposauroidea | A small, gracile archosaur, the only known "rauisuchians" with semiaquatic andpiscivorous habits owing to its narrow skull and tall tail vertebrae. |  |
| Rauisuchus | Huene | 1942 | Brazil | UpperSanta Maria Formation (Hyperodapedon Assemblage Zone) | Middle-lateCarnian | Rauisuchidae | Loricata (Rauisuchidae) | The namesake of Rauisuchia. Known primarily from skull, vertebral, and hindlimb fossils, which reconstruct a stocky quadrupedal predator with a boxy skull full of serrated teeth. |  |
| Saurosuchus | Reig | 1959 | Argentina | Ischigualasto Formation | LateCarnian | Prestosuchidae | Loricata (Prestosuchidae?) | A very large quadruped which lived alongside some of the earliest dinosaurs. Fossils include a well-preserved cranium. |  |
| Scolotosuchus | Sennikov | 2023 | Russia | Lipovskaya Formation | LateOlenekian | Rauisuchidae | "Rauisuchidae" | A large rauisuchian based on distinctive vertebrae. | |
| Shuvosaurus | Chatterjee | 1993 | United States | Cooper Canyon Formation | Early-middleNorian | Theropoda / "Chatterjeeidae" | Poposauroidea (Shuvosauridae) | An unusual beaked biped with two sets of fossils independently discovered in the mid-1990s: a toothless skull (Shuvosaurus) attributed to an ornithomimosaur-like dinosaur, and postcranial material ("Chatterjeea") comparable to poposaurids. The synonymy between these two fossil sets would not be confirmed until the discovery ofEffigia, a close relative. |  |
| Sillosuchus | Alcober & Parrish | 1997 | Argentina | Ischigualasto Formation | LateCarnian | Poposauridae | Poposauroidea (Shuvosauridae) | A probable relative ofEffigia andShuvosaurus based on its vertebrae and hip fossils. May have reached up to 10 meters (33 ft) in length according to a large isolated vertebra. |  |
| Stagonosuchus | Huene | 1938 | Tanzania | Manda Formation | Anisian? toCarnian? | Prestosuchidae | Loricata | A Tanzanian archosaur named from hip and vertebral fragments. May be a species ofPrestosuchus. | |
| Teratosaurus | Meyer | 1861 | Germany | Löwenstein Formation (Stubensandstein) | Norian | Carnosauria /Rauisuchidae /Poposauridae | Loricata (Rauisuchidae?) | The earliest "rauisuchian" to be named, though itsholotype fossil (a toothedmaxilla bone) was misidentified as that of an earlycarnosaurian dinosaur. A complete re-evaluation of archosaur systematics in the 1980s involved the recognition thatTeratosaurus (and other "rauisuchians") were completely unrelated to carnosaurian dinosaurs. |  |
| Ticinosuchus | Krebs | 1965 |  Switzerland, | Mittlere Grenzbitumenzone | LateAnisian | Prestosuchidae | Suchia (non-paracrocodylomorph) | Described from a flattened but complete skeleton fromMonte San Giorgio on the Swiss-Italian border. Its discovery established knowledge of "rauisuchian" proportions and their association withchirothere footprints. Commonly considered the sister taxon to Paracrocodylomorpha. |  |
| Tikisuchus | Chatterjee & Majumdar | 1987 |  India | Tiki Formation | Carnian? | Rauisuchidae | Loricata (Rauisuchidae?) | A medium-sized probable rauisuchid with a proportionally large skull. | |
| Vivaron | Lessneret al. | 2016 | United States | Chinle Formation (Petrified Forest Member) | MiddleNorian | N/A | Loricata (Rauisuchidae) | Known fromPostosuchus-like skull and hip fragments from the Hayden Quarry atGhost Ranch,New Mexico. Its discovery casts doubt on the assumption that all rauisuchid fossils from the southwestern United States can be referred toPostosuchus. |  |
| Xilousuchus | Wu | 1981 | China | Heshanggou Formation | LateOlenekian or earlyAnisian | Proterosuchidae /Erythrosuchidae | Poposauroidea (Ctenosauriscidae) | One of the better-understood early "rauisuchians", actenosauriscid including skull, braincase, and cervical (neck) fossils. | |
| Youngosuchus | Young | 1973 | China | Ermaying Formation | Anisian? | Erythrosuchidae /Rauisuchidae? | Loricata | Based on a well-preserved but poorly-described partial skeleton, including a skull. Originally named as a species ofVjushkovia, anerythrosuchid which has subsequently been synonymized withGarjainia. |  |
