Product Code Database
" Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic . Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to than to birds and other . 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 Taxonomy group, were considered distinct from other Triassic archosaur groups such as early dinosaurs, (crocodile-like carnivores), (armored herbivores), and Crocodylomorpha (lightly-built crocodilian ancestors).
However, more recent studies on archosaur evolution have upended this idea based on phylogenetic analyses and cladistics, a modern approach to taxonomy based on (nested Monophyly groups of common ancestry). Since the early 2010s, archosaur classification schemes have stabilized on a system where Rauisuchia is rendered an evolutionary grade, or even a wastebin taxon. Crocodylomorpha most likely originated from a rauisuchian ancestor based on a myriad of shared traits, and some "rauisuchians" (such as Postosuchus and Rauisuchus) appear to be more closely related to crocodylomorphs than to other "rauisuchians" (such as Prestosuchus and Saurosuchus).
As a result, Rauisuchia in its traditional usage may be considered paraphyletic: 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 Monophyly groups have been erected to classify "rauisuchians" in a cladistic framework. The closest concept is the clade Paracrocodylomorpha, 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) and Loricata, which includes most typical "rauisuchians" and crocodylomorphs.
"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). ‘Rauisuchian’ material from the lower Elliot Formation of South Africa and Lesotho: Implications for Late Triassic biogeography and biostratigraphy 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 the Jurassic, 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, which was named after fossil collector Dr. Wilhelm Rau. The name Rauisuchus means Wilhelm Rau's crocodile.
There has been considerable suggestion that the group as currently defined is paraphyletic, 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 than to prestosuchids. Nesbitt (2003) presented a different phylogeny with a monophyletic 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 of Batrachotomus (2002) and restudies of other forms, such as Erpetosuchus (2002) have shed some light on the evolutionary relationships of this poorly known group.
In a study of the Ctenosauriscidae Arizonasaurus, paleontologist Sterling Nesbitt defined a clade of rauisuchians called "Group X". This group includes Arizonasuchus, Lotosaurus, Sillosuchus, Shuvosaurus, and Effigia. One distinguishing feature of Group X is their lack of osteoderms, which are common among many other . Many more features are found in the pelvis, including fully fused sacral vertebrae and a long, thin crest on the ilium called the supra-acetabular crest. Additionally, many members of Group X have smooth frontal bone and , which make up the upper portion of the rostrum. In other "rauisuchians" and many other crurotarsans, this area has bumps and ridges. "Group X" is now termed Poposauroidea.
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 , which is also seen in theropod (a case of evolutionary convergence). In addition, the cervical vertebrae that make up the neck are strongly amphicoelus, meaning that they are concave at both ends. The fourth trochanter, a ridge of bone on the femur for muscle attachment seen in nearly all archosaurs, is absent in Group Y. "Group Y" is now termed Shuvosauridae.
Although not placed within Group Y, Lotosaurus shares many similarities with members of the clade, foremost of which is edentulism, 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 between basal members of Group X and members of Group Y.
Below is the cladogram 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 and Ticinosuchus. Poposauroidea included poposaurids and ctenosauriscids, but the phylogeny had a large polytomy of genera in both groups that was difficult to resolve, which included Arizonasaurus, Poposaurus, 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 at the base of the clade Paracrocodylomorpha, and the rest of the "rauisuchians" forming a grade within the clade Loricata. 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.
The oldest known "rauisuchians", in terms of geological age, are probably from the end of the Early Triassic (late Olenekian). Most of these early fossils are fragmentary and dubious remains from Russia, but some are better-described and constrained, such as Xilousuchus, a Ctenosauriscidae 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, from the "siltstone member" of the Chinle Formation in New Mexico, may be as young as the Rhaetian, the last stage of the Triassic. Effigia was recovered from the Coelophysis Quarry of Ghost Ranch.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 of South Africa may be even younger, late Rhaetian or possibly even lowermost Jurassic.
Fossil record
Well-known "rauisuchians" include Ticinosuchus of the Middle Triassic of Switzerland and Northern Italy, Saurosuchus of the Late Triassic (late Carnian) of Argentina, Prestosuchus of the Middle-Late Triassic (late Ladinian-early Carnian) of Brazil, and Postosuchus of the Late Triassic (Norian) of the southwest United States. The first "rauisuchian" known to paleontology was Teratosaurus, a German genus from the Late Triassic (Norian) of Germany. However, Teratosaurus was considered an early theropod 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) and emphasized further by the description of Ticinosuchus in the 1960s.
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, Jushatyria, Scythosuchus, Tsylmosuchus, Vjushkovisaurus, Vytshegdosuchus) and China ( Fenhosuchus, Wangisuchus), nor taxa reclassified as non-"rauisuchian" archosaurs ( Ornithosuchus, Gracilisuchus, Dongusuchus, Yarasuchus).
Apatosuchus Sues & Schoch 2013 Löwenstein Formation (Stubensandstein) Norian Theropoda Loricata A small "rauisuchian" based on a partial skull. Originally considered a species of Halticosaurus, a contemporary theropod dinosaur. Arganasuchus Jalil & Peyer 2007 Timezgadiouine Formation Carnian? Rauisuchidae Loricata A "rauisuchian" based on scant skull and postcranial material similar to that of Batrachotomus, Luperosuchus, and Postosuchus. Arizonasaurus Welles 1947 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 with Poposauroidea. Batrachotomus Gower 1999 Erfurt Formation (Lower Keuper) Late Ladinian Prestosuchidae / Rauisuchidae Loricata One of the most completely-known "rauisuchians", with numerous fossils recovered from sites at Kupferzell, Crailsheim and Vellberg-Eschenau. Bromsgroveia Peter Galton 1985 Bromsgrove Sandstone Anisian Theropoda / Temnospondyli /Poposauridae Poposauroidea (Ctenosauriscidae) Named based on a distinctive Poposauroidea-like ilium, but also possibly incorporating "rauisuchian" fossil material such as teeth and described from England since the mid-19th century. Bystrowisuchus Sennikov 2012 Lipovskaya Formation (Gamskian Gorizont) Late Olenekian? Ctenosauriscidae Poposauroidea (Ctenosauriscidae) An early ctenosauriscid with low-spined cervical (neck) vertebrae similar to Xilousuchus. Ctenosauriscus Oskar Kuhn 1964 Solling Formation Late Olenekian to Anisian? "" / Temnospondyli / Ctenosauriscidae Poposauroidea (Ctenosauriscidae) Known from slabs of sail-backed dorsal vertebrae first discovered in 1871 and originally named as the (preoccupied) genus Ctenosaurus in 1902. Its affinities were strongly debated until stabilizing as poposauroid archosaur upon the discovery of new Arizonasaurus and Lotosaurus fossils . Dagasuchus Lacerda et al. 2015 Middle Santa Maria Formation ( Santacruzodon Assemblage Zone) Late Ladinian or early Carnian N/A Loricata A medium-sized "rauisuchian" based on a hip bone which helps to fill a gap in the Biostratigraphy record of Brazilian archosaurs. Decuriasuchus França 2011 Lower Santa Maria Formation ( Dinodontosaurus Assemblage Zone) Late Ladinian or early Carnian Prestosuchidae Loricata A medium-sized "rauisuchian" named from 10 individuals (including several nearly-complete skeletons) which died and fossilized together, suggesting a gregarious social structure. Effigia Sterling Nesbitt & Mark Norell 2006 Chinle Formation ("siltstone member") Late Norian or Rhaetian Derived Suchia Poposauroidea (Shuvosauridae) A bizarre pseudosuchian convergent on Ornithomimidae, with a toothless skull, theropod-like hip, and very short arms. Discovered within a sediment block collected from the Coelophysis Quarry of Ghost Ranch, New Mexico. Etjosuchus Tolchard et al. 2021 Omingonde Formation Ladinian or early Carnian Erythrosuchidae Loricata A large and possibly bipedal "rauisuchian" based on a partial skeleton previously misattributed to the erythrosuchid Erythrosuchus. Fasolasuchus Bonaparte 1981 Los Colorados Formation Late Norian Rauisuchidae Loricata One of the last and largest "rauisuchians", occurring alongside an increasingly diverse fauna of sauropodomorph dinosaurs. Heptasuchus Dawley et al. 1979 Popo Agie Formation Late Carnian? Prestosuchidae? Loricata One of the oldest predatory archosaurs from North America, based on skull and postcranial fragments from Wyoming. Probably a close relative of Batrachotomus. Hypselorhachis Butler et al. 2009 Manda Formation Anisian? to Carnian? Ctenosauriscidae Poposauroidea (Ctenosauriscidae) A ctenosauriscid based on a single well-preserved vertebra with a very long neural spine. First mentioned in an unpublished 1966 by Alan Charig, but not formally described until 2009. Lotosaurus Zhang 1975 Badong Formation Anisian? to Carnian? "Lotosauridae" Poposauroidea An unusual quadruped combining a neural spine sail with a toothless skull. Known from abundant fossils clustered into a Bone bed, but most of these fossils remain undescribed. Luperosuchus Romer 1971 Chanares Formation ( Tarjadia Assemblage Zone) Late Ladinian or earliest Carnian Prestosuchidae Loricata
(Prestosuchidae?) A medium-sized "rauisuchian" with a skull similar to Prestosuchus and Saurosuchus. Mambawakale Butler et al. 2022 Manda Formation Anisian? to Carnian? "Pallisteriidae" Basal Paracrocodylomorpha? A possible paracrocodylomorph based on a massive partial skull. Mentioned as " Pallisteria angustimentum" in an unpublished 1967 manuscript by Alan Charig, but not formally described (and provided a new scientific name) until 2022. Mandasuchus Butler et al. 2018 Manda Formation Anisian? to Carnian? Prestosuchidae? Basal Paracrocodylomorpha? One of the most basal loricatans or poposauroids, first mentioned in a 1956 doctoral thesis by Alan Charig but not formally described until 2018. Polonosuchus Brusatte et al. 2009 Krasiejów claypit Late Carnian? Rauisuchidae Loricata (Rauisuchidae) A large rauisuchid, formerly named as a species of Teratosaurus and currently considered a close relative of Postosuchus. Poposaurus Mehl 1915 Popo Agie Formation, Dockum Group, Chinle Formation (Monitor Butte Member, Blue Mesa Member, Sonsela Member) Late Carnian? to middle Norian / 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 in Utah in 2003. Postosuchus Chatterjee 1985 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 to Tyrannosauridae when first described. Prestosuchus Huene 1942 Lower Santa Maria Formation ( Dinodontosaurus Assemblage Zone) Late Ladinian or early Carnian 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 Lower Santa Maria Formation ( Dinodontosaurus Assemblage Zone) Late Ladinian or early Carnian Prestosuchidae Loricata (Prestosuchidae?) A poorly-known taxon, possibly a synonym or species of Prestosuchus. Qianosuchus Li et al. 2006 Guanling Formation (Panxian biota) Anisian Indeterminate Crurotarsi Poposauroidea A small, gracile archosaur, the only known "rauisuchians" with semiaquatic and Piscivore habits owing to its narrow skull and tall tail vertebrae. Rauisuchus Huene 1942 Upper Santa Maria Formation ( Hyperodapedon Assemblage Zone) Middle-late Carnian 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 Ischigualasto Formation Late Carnian Prestosuchidae Loricata (Prestosuchidae?) A very large quadruped which lived alongside some of the earliest dinosaurs. Fossils include a well-preserved cranium. Scolotosuchus Sennikov 2023 Lipovskaya Formation Late Olenekian Rauisuchidae "Rauisuchidae" A large rauisuchian based on distinctive vertebrae. Shuvosaurus Chatterjee 1993 Cooper Canyon Formation Early-middle Norian 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 of Effigia, a close relative. Sillosuchus Alcober & Parrish 1997 Ischigualasto Formation Late Carnian Poposauridae Poposauroidea (Shuvosauridae) A probable relative of Effigia and Shuvosaurus 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 Manda Formation Anisian? to Carnian? Prestosuchidae Loricata A Tanzanian archosaur named from hip and vertebral fragments. May be a species of Prestosuchus. Teratosaurus Meyer 1861 Löwenstein Formation (Stubensandstein) Norian Carnosauria / Rauisuchidae / Poposauridae Loricata (Rauisuchidae?) The earliest "rauisuchian" to be named, though its holotype fossil (a toothed maxilla bone) was misidentified as that of an early dinosaur. A complete re-evaluation of archosaur systematics in the 1980s involved the recognition that Teratosaurus (and other "rauisuchians") were completely unrelated to carnosaurian dinosaurs. Ticinosuchus Krebs 1965 ,
Mittlere Grenzbitumenzone Late Anisian Prestosuchidae Suchia (non-paracrocodylomorph) Described from a flattened but complete skeleton from Monte San Giorgio on the Swiss-Italian border. Its discovery established knowledge of "rauisuchian" proportions and their association with Chirotherium footprints. Commonly considered the sister taxon to Paracrocodylomorpha. Tikisuchus Chatterjee & Majumdar 1987 Tiki Formation Carnian? Rauisuchidae Loricata (Rauisuchidae?) A medium-sized probable rauisuchid with a proportionally large skull. Vivaron Lessner et al. 2016 Chinle Formation (Petrified Forest Member) Middle Norian N/A Loricata (Rauisuchidae) Known from Postosuchus-like skull and hip fragments from the Hayden Quarry at Ghost Ranch, New Mexico. Its discovery casts doubt on the assumption that all rauisuchid fossils from the southwestern United States can be referred to Postosuchus. Xilousuchus Wu 1981 Heshanggou Formation Late Olenekian or early Anisian Proterosuchidae / Erythrosuchidae Poposauroidea (Ctenosauriscidae) One of the better-understood early "rauisuchians", a Ctenosauriscidae including skull, braincase, and cervical (neck) fossils. Youngosuchus Young 1973 Ermaying Formation Anisian? Erythrosuchidae /Rauisuchidae? Loricata Based on a well-preserved but poorly-described partial skeleton, including a skull. Originally named as a species of Vjushkovia, an Erythrosuchidae which has subsequently been synonymized with Garjainia.
See also
Notes
|
|
