In the geologic timescale , the Wordian is an age or stage of the Permian . It is the middle of three subdivisions of the Guadalupian Epoch or Series . The Wordian lasted between 266.9 and 264.28 million years ago (Ma) . It was preceded by the Roadian and followed by the Capitanian .
25-547: See Taxonomy Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event . Dinocephalians included herbivorous , carnivorous , and omnivorous forms. Many species had thickened skulls with many knobs and bony projections. Dinocephalians were
50-534: 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
75-479: 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
100-623: 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
125-549: A crushing surface when the jaws were shut. Most dinocephalians also developed pachyostosis of the bones in the skull, which seems to have been an adaptation for intra-specific behaviour (head-butting), perhaps for territory or a mate. In some types, such as Estemmenosuchus and Styracocephalus , there are also horn-like structures, which evolved independently in each case. Anteosauridae Estemmenosuchidae Styracocephalidae Titanosuchidae Tapinocephalidae The dinocephalians are an ancient group and their ancestry
150-422: 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
175-429: 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 ,
200-499: 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,
225-476: 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
250-785: Is located at Getaway Ledge in the Guadalupe Mountains of Texas . The top of the Wordian (the base of the Capitanian Stage) is defined as the place in the stratigraphic record where the conodont species Jinogondolella postserrata first appears. The Wordian stage was part of the time in which the Zechstein was deposited in Europe. The Wordian spans the entire conodont biozone of Jinogondolella aserrata . It contains two fusulinid biozones: Olson’s Extinction ,
275-582: Is not clear. It is assumed that they must have evolved during the earlier part of the Roadian , or possibly even the Kungurian epoch, but no trace has been found. These animals radiated at the expense of the dying pelycosaurs , who dominated during the early part of the Permian and may have even gone extinct due to competition with therapsids, especially the short-lived but most dominant dinocephalians. Even
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#1732772178835300-515: 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
325-489: 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
350-692: The North American Permian Basin . The Wordian was first used as a stratigraphic subdivision of the Guadalupian in 1961, when both names were still only used regionally in the southern US. The stage was added to the internationally used ISC timescale in 2001. The base of the Wordian Stage is defined as the place in the stratigraphic record where fossils of conodont species Jinogondolella aserrata first appear. The global reference profile for this stratigraphic boundary
375-690: The earliest members, the estemmenosuchids and early brithopodids of the Russian Ocher fauna, were already a diverse group of herbivores and carnivores. During the Wordian and early Capitanian , advanced dinocephalians radiated into a large number of herbivorous forms, representing a diverse megafauna . This is well known from the Tapinocephalus Assemblage Zone of the Southern African Karoo . At
400-632: The expansion of the ilium and more erect limbs. They include carnivorous , herbivorous , and omnivorous forms. Some, like Keratocephalus , Moschops , Struthiocephalus and Jonkeria were semiaquatic , others, like Anteosaurus , were more terrestrial. Dinocephalians were among the largest animals of the Permian period; only the biggest caseids and pareiasaurs reaching them in size. Dinocephalians were generally large. The biggest herbivores ( Tapinocephalus ) and omnivores ( Titanosuchus ) may have weighed up to 2 tonnes (4,400 lb), and were some 4.5 metres (15 ft) long, while
425-518: The first non-mammalian therapsids to be scientifically described and their fossils are known from Russia, China, Brazil, South Africa, Zimbabwe, and Tanzania. Apart from the biarmosuchians , the dinocephalians are the least advanced therapsids, although still uniquely specialised in their own way. They retain a number of primitive characteristics (e.g. no secondary palate , small dentary ) shared with their pelycosaur ancestors, although they are also more advanced in possessing therapsid adaptations like
450-451: 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
475-546: 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"
500-531: The height of their diversity (middle or late Capitanian age) all the dinocephalians suddenly died out, during the Capitanian mass extinction event . The reason for their extinction is not clear; although disease, sudden climatic change, or other factors of environmental stress may have brought about their end. They were replaced by much smaller therapsids ; herbivorous dicynodonts and carnivorous biarmosuchians , gorgonopsians and therocephalians . [REDACTED] Clade In biological phylogenetics ,
525-420: The largest carnivores (such as Titanophoneus and Anteosaurus ) were at least as long, with heavy skulls 80 centimetres (31 in) long, and overall masses of around a half-tonne. All dinocephalians are distinguished by the interlocking incisor (front) teeth. Correlated features are the distinctly downturned facial region, a deep temporal region, and forwardly rotated suspensorium. Shearing contact between
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#1732772178835550-590: 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"
575-518: 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
600-527: 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. Wordian The Wordian Stage was introduced into scientific literature by Johan August Udden in 1916 and was named after the Word Formation of
625-441: The upper and lower teeth (allowing food to be more easily sliced into small bits for digestion) is achieved through keeping a fixed quadrate and a hinge-like movement at the jaw articulation. The lower teeth are inclined forward, and occlusion is achieved by the interlocking of the incisors. The later dinocephalians improved on this system by developing heels on the lingual sides of the incisor teeth that met against one another to form
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