57-477: " Rauisuchia " is a paraphyletic group of mostly large and carnivorous Triassic archosaurs . Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia , which encompasses all archosaurs more closely related to crocodilians than to birds and other dinosaurs . 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
114-479: A "single common ancestor" organism. Paraphyly is common in speciation , whereby a mother species (a paraspecies ) gives rise to a daughter species without itself becoming extinct. Research indicates as many as 20 percent of all animal species and between 20 and 50 percent of plant species are paraphyletic. Accounting for these facts, some taxonomists argue that paraphyly is a trait of nature that should be acknowledged at higher taxonomic levels. Cladists advocate
171-592: A cell nucleus, a plesiomorphy ) from its excluded descendants. Also, some systematists recognize paraphyletic groups as being involved in evolutionary transitions, the development of the first tetrapods from their ancestors for example. Any name given to these hypothetical ancestors to distinguish them from tetrapods—"fish", for example—necessarily picks out a paraphyletic group, because the descendant tetrapods are not included. Other systematists consider reification of paraphyletic groups to obscure inferred patterns of evolutionary history. The term " evolutionary grade "
228-418: 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
285-419: A group of dinosaurs (part of Diapsida ), both of which are "reptiles". Osteichthyes , bony fish, are paraphyletic when circumscribed to include only Actinopterygii (ray-finned fish) and Sarcopterygii (lungfish, etc.), and to exclude tetrapods ; more recently, Osteichthyes is treated as a clade, including the tetrapods. The " wasps " are paraphyletic, consisting of the narrow-waisted Apocrita without
342-439: A kind of lizard). Put another way, viviparity is a synapomorphy for Theria within mammals, and an autapomorphy for Eulamprus tympanum (or perhaps a synapomorphy, if other Eulamprus species are also viviparous). Groupings based on independently-developed traits such as these examples of viviparity represent examples of polyphyly , not paraphyly. The following list recapitulates a number of paraphyletic groups proposed in
399-648: A large number of non-"rauisuchian" taxa as controls. 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
456-573: A modern approach to taxonomy based on clades (nested monophyletic 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 . Crocodylomorphs 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
513-560: A more inclusive clade, it often makes sense to study the paraphyletic group that remains without considering the larger clade. For example, the Neogene evolution of the Artiodactyla (even-toed ungulates, like deer, cows, pigs and hippopotamuses - Cervidae , Bovidae , Suidae and Hippopotamidae , the families that contain these various artiodactyls, are all monophyletic groups) has taken place in environments so different from that of
570-423: 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
627-551: 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): Arganasuchus Fasolasuchus Stagonosuchus Ticinosuchus Saurosuchus Batrachotomus Prestosuchus Tikisuchus Rauisuchus Postosuchus Teratosaurus Yarasuchus Qianosuchus Arizonasaurus Bromsgroveia Lotosaurus Poposaurus Sillosuchus Effigia Shuvosaurus In
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#1732798025503684-424: A phylogenetic species concept that does not consider species to exhibit the properties of monophyly or paraphyly, concepts under that perspective which apply only to groups of species. They consider Zander's extension of the "paraphyletic species" argument to higher taxa to represent a category error When the appearance of significant traits has led a subclade on an evolutionary path very divergent from that of
741-478: A pillar-erect hip posture, though exceptions exist for all of these traits. Rauisuchians, as a traditional taxonomic group, were considered distinct from other Triassic archosaur groups such as early dinosaurs, phytosaurs (crocodile-like carnivores), aetosaurs (armored herbivores), and crocodylomorphs (lightly-built crocodilian ancestors). However, more recent studies on archosaur evolution have upended this idea based on phylogenetic analyses and cladistics ,
798-424: 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 monophyletic groups have been erected to classify "rauisuchians" in a cladistic framework. The closest concept
855-419: 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 contrast, a monophyletic grouping (a clade ) includes a common ancestor and all of its descendants. The terms are commonly used in phylogenetics (a subfield of biology ) and in
912-416: Is a cladogram from Ezcurra (2016) that reexamined all historical members of the "Proterosuchia" (a polyphyletic historical group including proterosuchids and erythrosuchids ). The placement of fragmentary taxa that had to be removed to increase tree resolution is indicated by dashed lines (in the most derived position that they can be confidently assigned to). Taxa that are nomina dubia are indicated by
969-696: 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 ). ( Prestosuchidae ?) [REDACTED] Italy [REDACTED] Paraphyletic group Paraphyly
1026-439: Is a monophyletic group from which one or more subsidiary clades (monophyletic groups) are excluded to form a separate group. Philosopher of science Marc Ereshefsky has argued that paraphyletic taxa are the result of anagenesis in the excluded group or groups. A cladistic approach normally does not grant paraphyletic assemblages the status of "groups", nor does it reify them with explanations, as in cladistics they are not seen as
1083-587: 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 edentulous , 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
1140-433: Is allowed as a synonym of Magnoliopsida. Phylogenetic analysis indicates that the monocots are a development from a dicot ancestor. Excluding monocots from the dicots makes the latter a paraphyletic group. Among animals, several familiar groups are not, in fact, clades. The order Artiodactyla ( even-toed ungulates ) as traditionally defined is paraphyletic because it excludes Cetaceans (whales, dolphins, etc.). Under
1197-423: Is diagnosed by the presence of four or more sacral vertebrae with fully fused neural arches , which is also seen in theropod dinosaurs (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,
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#17327980255031254-635: 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
1311-442: Is paraphyletic with respect to birds . Reptilia contains the last common ancestor of reptiles and all descendants of that ancestor except for birds. Other commonly recognized paraphyletic groups include fish , monkeys , and lizards . The term paraphyly , or paraphyletic , derives from the two Ancient Greek words παρά ( pará ), meaning "beside, near", and φῦλον ( phûlon ), meaning "genus, species", and refers to
1368-465: Is small, the fourth trochanter , a ridge on the femur that serves as a muscle attachment in archosaurs, first appears in erythrosuchids. The triradiate pelvis and fourth trochanter are both features which indicate that erythrosuchids had an erect stance similar to later archosaurs. More basal archosauriforms such as proterosuchids lacked these features and probably had a more sprawling posture. Erythrosuchids were formerly classified as thecodonts of
1425-482: Is sometimes used for paraphyletic groups. Moreover, the concepts of monophyly , paraphyly, and polyphyly have been used in deducing key genes for barcoding of diverse group of species. Current phylogenetic hypotheses of tetrapod relationships imply that viviparity , the production of offspring without the external laying of a fertilized egg, developed independently in the lineages that led to humans ( Homo sapiens ) and southern water skinks ( Eulampus tympanum ,
1482-598: Is the cladogram from Nesbitt (2007): Postosuchus Rauisuchus Arizonasaurus Lotosaurus Sillosuchus Shuvosaurus Effigia 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
1539-437: 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" had an erect gait with their legs oriented vertically beneath
1596-514: The Cetacea (whales, dolphins, and porpoises) that the Artiodactyla are often studied in isolation even though the cetaceans are a descendant group. The prokaryote group is another example; it is paraphyletic because it is composed of two Domains (Eubacteria and Archaea) and excludes (the eukaryotes ). It is very useful because it has a clearly defined and significant distinction (absence of
1653-581: The ICN ) abandoned consideration of bacterial nomenclature in 1975; currently, prokaryotic nomenclature is regulated under the ICNB with a starting date of 1 January 1980 (in contrast to a 1753 start date under the ICBN/ICN). Among plants, dicotyledons (in the traditional sense) are paraphyletic because the group excludes monocotyledons . "Dicotyledon" has not been used as a botanic classification for decades, but
1710-542: The Karoo Basin), China, India and European Russia, from the Early to Middle Triassic . Erythrosuchids were unusually large and robust archosauromorphs. Several features set them apart from other archosauriformes and are also seen in later, more derived archosaurs . For example, they lack teeth on the palate , which are found in other early archosauriformes, such as Doswellia and euparkeriids . In erythrosuchids,
1767-564: The Olenekian 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 , 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
Rauisuchia - Misplaced Pages Continue
1824-721: The Rhaetian , the last stage of the Triassic. Effigia was recovered from the Coelophysis Quarry of Ghost Ranch . 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. The following
1881-660: The ants and bees . The sawflies ( Symphyta ) are similarly paraphyletic, forming all of the Hymenoptera except for the Apocrita, a clade deep within the sawfly tree. Crustaceans are not a clade because the Hexapoda (insects) are excluded. The modern clade that spans all of them is the Tetraconata . One of the goals of modern taxonomy over the past fifty years has been to eliminate paraphyletic "groups", such as
1938-400: The centra (central parts of vertebrae) are deeply indented on either side, differing considerably from the usual cylindrical shape of the centra in early archosauriformes, but similar to later archosaurs. The heads of erythrosuchids are generally disproportionately large and deep. In all erythrosuchids, the lower margin of the premaxilla , the bone at the tip of the upper jaw, is lower than
1995-536: 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 and nasal bones , 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
2052-448: The tree model of historical linguistics . Paraphyletic groups are identified by a combination of synapomorphies and symplesiomorphies . If many subgroups are missing from the named group, it is said to be polyparaphyletic. The term received currency during the debates of the 1960s and 1970s accompanying the rise of cladistics , having been coined by zoologist Willi Hennig to apply to well-known taxa like Reptilia ( reptiles ), which
2109-542: The Triassic. Along with many other large archosaurs, the group died out in the Triassic-Jurassic extinction event (barring crocodylomorphs, which survive to the present in the form of crocodilians). 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
2166-495: The actual products of evolutionary events. A group whose identifying features evolved convergently in two or more lineages is polyphyletic (Greek πολύς [ polys ], "many"). More broadly, any taxon that is not paraphyletic or monophyletic can be called polyphyletic. Empirically, the distinction between polyphyletic groups and paraphyletic groups is rather arbitrary, since the character states of common ancestors are inferences, not observations. These terms were developed during
2223-440: 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 (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
2280-490: The debates of the 1960s and 1970s accompanying the rise of cladistics . Paraphyletic groupings are considered problematic by many taxonomists, as it is not possible to talk precisely about their phylogenetic relationships, their characteristic traits and literal extinction. Related terms are stem group , chronospecies , budding cladogenesis, anagenesis, or 'grade' groupings. Paraphyletic groups are often relics from outdated hypotheses of phylogenic relationships from before
2337-478: The descendants of a unique common ancestor. By comparison, the term polyphyly , or polyphyletic , uses the Ancient Greek prefix πολύς ( polús ), meaning "many, a lot of", and refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources. Groups that include all the descendants of a common ancestor are said to be monophyletic . A paraphyletic group
Rauisuchia - Misplaced Pages Continue
2394-537: 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 (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 ctenosauriscid from the Heshanggou Formation of China. Xilousuchus
2451-523: The evolutionary relationships of this poorly known group. Despite its inclusion as an informal grouping in numerous phylogenetic 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
2508-450: The examples given here, from formal classifications. Species have a special status in systematics as being an observable feature of nature itself and as the basic unit of classification. Some articulations of the phylogenetic species concept require species to be monophyletic, but paraphyletic species are common in nature, to the extent that they do not have a single common ancestor. Indeed, for sexually reproducing taxa, no species has
2565-399: 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
2622-414: The genus Rauisuchus , which was named after fossil collector Dr. Wilhelm Rau . The name Rauisuchus means Wilhelm Rau's crocodile. "Rauisuchians" were originally thought to be related to erythrosuchids , but it is now known that they are pseudosuchians . Three families have historically been recognised: Prestosuchidae , Rauisuchidae , and Poposauridae , as well as a number of forms (e.g. those from
2679-622: The island of Taiwan . Erythrosuchidae see below 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 ). The family Erythrosuchidae was named by David Meredith Seares Watson in 1917. They were the apex predators of their day, with lengths of 2.5 m (8 ft 2 in) to almost 5 m (16 ft). Their fossil remains are known to date from South Africa ( Beaufort Group of
2736-622: The literature, and provides the corresponding monophyletic taxa. The concept of paraphyly has also been applied to historical linguistics , where the methods of cladistics have found some utility in comparing languages. For instance, the Formosan languages form a paraphyletic group of the Austronesian languages because they consist of the nine branches of the Austronesian family that are not Malayo-Polynesian and are restricted to
2793-486: The lower margin of the maxilla , the bone behind the premaxilla. This forms a characteristic "step" that makes erythrosuchids easily distinguishable from all other early archosauriformes, which have smooth jaw margins that are either straight or gradually curved. Erythrosuchids are notable for being the first archosauriforms to have a triradiate pelvic girdle with three projecting areas formed from three bones: an ilium and an elongated pubis and ischium . Although it
2850-696: The ranks of the ICZN Code , the two taxa are separate orders. Molecular studies, however, have shown that the Cetacea descend from artiodactyl ancestors, although the precise phylogeny within the order remains uncertain. Without the Cetaceans the Artiodactyls are paraphyletic. The class Reptilia is paraphyletic because it excludes birds (class Aves ). Under a traditional classification, these two taxa are separate classes. However birds are sister taxon to
2907-567: The rise of cladistics. The prokaryotes (single-celled life forms without cell nuclei) are a paraphyletic grouping, because they exclude the eukaryotes , a descendant group. Bacteria and Archaea are prokaryotes, but archaea and eukaryotes share a common ancestor that is not ancestral to the bacteria. The prokaryote/eukaryote distinction was proposed by Edouard Chatton in 1937 and was generally accepted after being adopted by Roger Stanier and C.B. van Niel in 1962. The botanical code (the ICBN, now
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#17327980255032964-405: The situation in which one or several monophyletic subgroups of organisms (e.g., genera, species) are left apart from all other descendants of a unique common ancestor. Conversely, the term monophyly , or monophyletic , builds on the Ancient Greek prefix μόνος ( mónos ), meaning "alone, only, unique", and refers to the fact that a monophyletic group includes organisms consisting of all
3021-484: 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
3078-510: The suborder Proterosuchia . This classification is no longer used by paleontologists , who now employ a cladistic approach. In this, erythrosuchids constitute an Archosauriformes clade that is an outgroup to the Archosauria proper. The presence of certain archosaurian features , such as the triradiate pelvic girdle , the fourth trochanter , and the third metatarsal longer than the fourth, indicate that erythrosuchids are closer to
3135-430: The term "Rauisuchia" be abandoned. In a study of the ctenosauriscid 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 crurotarsans . Many more features are found in
3192-1000: The true archosaurs than the Proterosuchidae , which lack these features. Thus the Erythrosuchidae occupy a transitional evolutionary position between the most primitive archisauriformes and more advanced Triassic archosaurs. The family was defined by Martin Ezcurra and colleagues in 2010 during the description of Koilamasuchus as "all taxa more closely related to Erythrosuchus africanus than to Proterosuchus fergusi or Passer domesticus (the house sparrow ). Bharitalasuchus Chalishevia Erythrosuchus Garjainia Guchengosuchus Shansisuchus Uralosaurus ? Vjushkovisaurus Cladogram from Parrish (1992): Proterosuchus Garjainia Erythrosuchus Shansisuchus Vjushkovia Fugusuchus Other archosauriformes Below
3249-511: Was Teratosaurus , a German genus from the Late Triassic (Norian) of Germany. However, Teratosaurus was considered an early theropod dinosaur for much of its history, 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
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