26-474: Qikiqtania (pronounced "kick-kiq-tani-ahh") is an extinct genus of elpistostegalian tetrapodomorph from the Late Devonian (early Frasnian stage) Fram Formation of Nunavut , Canada . The genus contains a single species, Q. wakei , known from a partial skeleton. Analysis of the fin bones suggests that Qikiqtania was well-suited to swimming, and likely incapable of walking or supporting itself out of
52-525: 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
78-479: 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
104-623: 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
130-578: A direct result of moving to an inland freshwater mode of living. Fossils of Panderichthys are dated to the Givetian (around 385 million years old) or the Frasnian (around 380–375 million years old ). Thus, the oldest bone remains of elpistostegalians appear in the late Middle Devonian or in the early Late Devonian. However, a series of trace fossils from the early Middle Devonian of Poland suggests that tetrapod-limbed animals may have existed as early as in
156-422: 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
182-429: 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 ,
208-499: 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,
234-471: 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
260-515: 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
286-489: 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
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#1732876471687312-466: The Eifelian , around 395 million years ago. Paleontologist and professor Per E. Ahlberg has identified the following traits as synapomorphic for Elpistostegalia (and thus Tetrapoda): The name, originally coined around the genus Elpistostege , later become a synonym for Panderichthyida. In most analyses, the group as traditionally imagined is actually an evolutionary grade , the last "fishes" of
338-498: The trunk , including the dorsal midline and flank , the pectoral fin , and the lateral line series. Analysis of the scales revealed sensory canals that would have permitted the animal to detect the flow of water around its body. The holotype individual would have had a total body length of around 75 cm (30 in), which is smaller than most elpistostegalians . Qikiqtania represents an elpistostegalian closely related to limbed tetrapods . In all phylogenetic analyses , it
364-569: The fossil material. The fin bones of Qikiqtania were not sturdy enough to support its body on land, so it would have lived entirely in the water. Its humerus does not show any indication of the well-developed muscle-attachment points seen in related semi- subaerial taxa. This is in contrast to Tiktaalik , which would have been able to prop itself up in shallow water or on land and use its limbs for support. The preserved scales are rhomboid in shape, generally similar to those of other finned elpistostegalians . Preserved scales have been found from
390-452: The fossil site. The specific name , " wakei ," honors the evolutionary biologist David Wake . Qikiqtania had strong jaws that would have allowed it to securely bite and hold prey. It had a row of teeth and fangs inside its mouth, and it would have drawn food into its mouth using suction. CT scans of the rock containing the fin revealed a complete limb inside. These scans allowed the describing authors to better understand and interpret
416-451: 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
442-546: 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"
468-590: 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"
494-518: 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
520-437: The more stable, atmospheric source of oxygen. Being shallow-water fishes, the elpistostegalians evolved many of the basic adaptions that later allowed the tetrapods to become terrestrial animals. The most important ones were the shift of main propulsion apparatus from the tail fin to the pectoral and pelvic fins, and a shift to reliance on lungs rather than gills as the main means of obtaining oxygen. Both of these appear to be
546-632: The paired fins of Elpistostege contained bones homologous to the phalanges (digit bones) of modern tetrapods . The analysis carried out in this study recovered Elpistostege as the sister taxon of all unequivocally digited vertebrates. Panderichthys [REDACTED] Tiktaalik [REDACTED] Elpistostege Ventastega [REDACTED] Acanthostega [REDACTED] Ichthyostega [REDACTED] Tulerpeton [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Clade In biological phylogenetics ,
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#1732876471687572-462: The site where Tiktaalik was discovered, but from a slightly lower horizon in the formation. In 2022, Thomas A. Stewart, Justin B. Lemberg, Ailis Daly, Edward B. Daeschler , and Neil H. Shubin named and described Qikiqtania wakei based on these remains. The generic name , " Qikiqtania ," is derived from the Inuktitut words " Qikiqtaaluk " and "Qikiqtani", which represent the traditional names for
598-777: The tetrapod stem line , though Chang and Yu (1997) treated them as the sister clade to Tetrapoda . Elpistostegalia was re-defined as a clade containing Panderichthys and tetrapods. Below is a cladogram from Swartz, 2012. Tristichopteridae [REDACTED] Tinirau Platycephalichthys Panderichthys [REDACTED] Tiktaalik [REDACTED] Elpistostege Elginerpeton [REDACTED] Ventastega [REDACTED] Acanthostega [REDACTED] Ichthyostega [REDACTED] Whatcheeriidae [REDACTED] Colosteidae [REDACTED] Crassigyrinus [REDACTED] Baphetidae [REDACTED] Tetrapoda [REDACTED] The 2020 study by Cloutier et al. revealed that
624-534: The water, as has been suggested for the closely related Tiktaalik . The holotype specimen of Qikiqtania , NUFV 137 , was discovered in 2004 in layers of the late Devonian ( Frasnian )-dated Fram Formation of southern Ellesmere Island , Nunavut , Canada. The holotype specimen consists of lower jaws , partial left upper jaw and palate , gulars , ceratohyals , an articulated left pectoral fin and various articulated scales . The fossil remains of Qikiqtania were discovered 1.5 km (0.93 mi) east of
650-616: Was considered an order of prehistoric lobe-finned fishes , it was cladistically redefined to include tetrapods. A rise in global oxygen content allowed for the evolution of large, predatory fish that were able to exploit the shallow tidal areas and swamplands as top predators. Several groups evolved to fill these niches, the most successful were the elpistiostegalians. In such environments, they would have been challenged by periodic oxygen deficiency. In comparable modern aquatic environments like shallow eutrophic lakes and swampland, modern lungfish and some genera of catfish also rely on
676-621: Was recovered as crownward to Panderichthys . The cladogram below displays the results of the phylogenetic analyses by Stewart et al . (2022): Elpistostege [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Elpistostegalian Elpistostegalia is a clade containing Panderichthys and all more derived tetrapodomorph taxa. The earliest elpistostegalians, combining fishlike and tetrapod -like characters, such as Tiktaalik , are sometimes called fishapods . Although historically Elpistostegalia (referred to as Panderichthyida )
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