31-508: Allokotosauria is a clade of early archosauromorph reptiles from the Middle to Late Triassic known from Asia , Africa , North America and Europe . Allokotosauria was first described and named when a new monophyletic grouping of specialized herbivorous archosauromorphs was recovered by Sterling J. Nesbitt, John J. Flynn, Adam C. Pritchard, J. Michael Parrish, Lovasoa Ranivoharimanana and André R. Wyss in 2015 . The name Allokotosauria
62-464: A basicranium (UMMP 7473). These additional remains have since been recognized as belonging to a variety of other Triassic animals, all of which were poorly known or unknown at the time: the femur to an aetosaur , possibly Desmatosuchus , the ilium to a herrerasaurid , either Chindesaurus or Caseosaurus , depending on the taxonomic authority, and the basicranium to the rauisuchian Postosuchus . Friedrich von Huene recognized it as
93-534: A clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are
124-593: A phylogenetic analysis focusing on relations within Allokotosauria and recovered Trilophosaurus jacobsi to be more closely related to S. caseanus than to the type species of Trilophosaurus , Trilophosaurus buettneri . To further test this possibility, the types of S. caseanus and T. jacobsi were scored separately from the referred Kahle Trilophosaurus Quarry elements (referred to T. jacobsi by Spielmann et al. (2008) or to S. caseanus by Spielmann et al. (2009)). A phylogenetic analysis recovered
155-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
186-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
217-583: A new azendohsaurid and recovered Pamelaria as an azendohsaurid. Choristodera Aenigmastropheus Protorosaurus Prolacertoides Jesairosaurus Tanystropheidae Teraterpeton hrynewichorum Trilophosaurus buettneri Spinosuchus caseanus (= "Trilophosaurus" jacobsi ) Pamelaria dolichotrachela Shringasaurus indicus Azendohsaurus laaroussii Azendohsaurus madagaskarensis Rhynchosauria Boreopricea Prolacertidae Tasmaniosaurus Archosauriformes Pritchard and Nesbitt (2017) found support for
248-469: A new genus in 1932, and named it in honor of Case. He considered it to be a " podokesaurid ". Since the 1970s, though, it has been considered a nondinosaurian. However, a review by Hunt et al. in 1998 suggested that it was a theropod, possibly a herrerasaurid, citing its hollow centra as evidence for dinosaurian affinities. In an abstract for the 1999 Society of Vertebrate Paleontology meeting and his unpublished thesis, Richards recognized that it had
279-539: A partial vertebral column (UMMP 7507) he'd discovered in 1921 from the Tecovas Member of the Carnian -age Upper Triassic Dockum Formation of Crosby County , Texas , as Coelophysis sp. ( Coelophysis at that time also being poorly known). He considered it to be about 2.5 meters (8.5 ft) long. Additional material was referred to it, including a femur (UMMP 3396), an ilium (UMMP 8870), and
310-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
341-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
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#1732779968203372-401: A variety of characters that are apomorphic for various dinosaur subgroups, but that these are also found in different basal archosaur groups, and that the poorly preserved, distorted, and reconstructed vertebrae offer no evidence for assignment to any major archosaur group; it does, though, show some resemblances to the trilophosaurs . Further review, as part of a larger series of papers on
403-584: A variety of groups over its history, from coelophysid dinosaur to pseudosuchian to uncertain theropod dinosaur and to Proterosuchidae . This uncertainty is not unusual, given that it was only known from a poorly preserved, wall-mounted, partial vertebral column of an animal that lived in a time of diverse, poorly known reptile groups. However, newly collected material and recent phylogenetic studies of early archosauromorphs suggest that it represents an advanced trilophosaurid very closely related to Trilophosaurus . In 1922, Ermine Cowles Case described
434-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
465-533: Is derived from Greek meaning "strange reptiles" in reference to unexpected grouping of early archosauromorph with a high disparity of features typically associated with herbivory . Nesbitt et al. (2015) defined the group as a stem-based taxon containing Azendohsaurus madagaskarensis and Trilophosaurus buettneri and all taxa more closely related to them than to Tanystropheus longobardicus , Proterosuchus fergusi , Protorosaurus speneri or Rhynchosaurus articeps . Therefore, Allokotosauria includes
496-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
527-436: Is nearly as likely to represent a basal azendohsaurid instead. Protorosaurus speneri Tanystropheidae Rhynchosauria Pamelaria dolichotrachela Teraterpeton hrynewichorum Trilophosaurus buettneri Spinosuchus caseanus (= "Trilophosaurus" jacobsi ) Azendohsaurus laaroussii Azendohsaurus madagaskarensis Prolacerta broomi Archosauriformes Sengupta et al. (2017) described
558-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
589-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
620-464: The Carnian to Norian stages of North America , England and potentially European Russia , though one member of the latter group, Variodens inopinatus , is known from Rhaetian . According to studies of Arctosaurus material from Cameron Island in Canada, the latter may have been an allokotosaurian because of the similarities with Azendohsaurus due to the presence of a posterior ridge from
651-426: The centrum to the diapophyses which extends from the diapophysis all the way to the posterior ventrolateral corner of the centrum. This ridge overhangs a deep groove in the lateral surface of the centrum. Allokotosauria is most notably characterized by wrinkled side surface of orbital border of the frontal bone , expanded and hooked quadrate bone head on the posterior side, and a prominent tubercle developed above to
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#1732779968203682-584: The evolution of dinosaurs in the Late Triassic by Sterling Nesbitt, Randall Irmis, and William Parker, found Spinosuchus to be a valid genus. However, the authors could not classify it beyond Archosauriformes , and disagreed with Richards' trilophosaur hypothesis . Justin Spielmann and colleagues published a redescription in 2009 that concluded Spinosuchus was a trilophosaurid closely related to Trilophosaurus . Nesbitt et al. (2015) performed
713-550: The families Azendohsauridae and Trilophosauridae by definition, as well as the potentially more basal Pamelaria which is closer to them than to other early archosauromorphs. Pamelaria is the earliest known allokotosaur, dating to the Anisian of India . Azendohsauridae is currently represented by a single genus Azendohsaurus known from the Ladinian to Carnian of Africa , while trilophosaurids are mostly known from
744-451: The fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
775-580: The glenoid fossa of the scapula , although there are other unambiguous traits that differentiate it from other early archosauromorphs. Below is a cladogram showing the phylogenetic relationships of Allokotosauria within Archosauromorpha as recovered by Nesbitt et al. (2015). Ezcurra (2016) also recovered a highly supported Allokotosauria with the same topology (including only Pamelaria , Azendohsaurus madagaskarensis and Trilophosaurus buettneri in his analysis), but noted that Pamelaria
806-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
837-682: The inclusion of Kuehneosauridae within Allokotosauria. Buffa et al. (2024) recovered Drepanosauromorpha as allokotosaurian archosauromorphs, specifically as the sister group of trilophosaurids. Malerisaurus robinsonae Azendohsaurus madagaskarensis Pamelaria dolichotrachela Teraterpeton hrynewichorum Spinosuchus caseanus Trilophosaurus buettneri Avicranium renestoi Hypuronector limnaios Vallesaurus cenensis Dolabrosaurus aquatilis Drepanosaurus unguicaudatus Megalancosaurus preonensis Clade In biological phylogenetics ,
868-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
899-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
930-649: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Spinosuchus caseanus Spinosuchus (meaning "spined crocodile ") is an extinct genus of trilophosaurid allokotosaur from the Late Triassic of Texas , southern United States. It has been assigned to
961-511: The three in a monophyletic clade to the exclusion of T. buettneri based on a single autapomorphy . Furthermore, the types of S. caseanus and T. jacobsi as well as the Kahle Quarry material all scored identically, suggesting that T. jacobsi not only should be reassigned to Spinosuchus , but in fact represents the junior synonym of its type and only species ( S. caseanus ). Nesbitt et al. (2015) refrained from officially synonymizing