38-553: Tristichopterids (Tristichopteridae) were a diverse and successful group of fish-like tetrapodomorphs living throughout the Middle and Late Devonian . They first appeared in the Eifelian stage of the Middle Devonian. Within the group sizes ranged from a few tens of centimeters ( Tristichopterus ) to several meters ( Hyneria and Eusthenodon ). Some tristichopterids share some of
76-479: 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
114-592: 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 "
152-407: A common ancestor are said to be monophyletic . A paraphyletic group 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
190-419: 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
228-439: 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
266-549: 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
304-424: 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
342-458: Is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish . Advanced forms transitional between fish and the early labyrinthodonts , such as Tiktaalik , have been referred to as " fishapods " by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains
380-433: 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
418-629: Is rather arbitrary, since the character states of common ancestors are inferences, not observations. These terms were developed during 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
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#1732859431028456-520: Is relatively well-known, and can be somewhat reliably inferred through Eusthenopteron . Eusthenopteron differs significantly from some later Carboniferous tetrapods in the apparent absence of a recognized larval stage and a definitive metamorphosis. In even the smallest known specimen of Eusthenopteron foordi (at 29 mm), the lepidotrichia cover all of the fins, which does not happen until after metamorphosis in genera like Polyodon . This might indicate that Eusthenopteron developed directly, with
494-436: 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 the tree model of historical linguistics . Paraphyletic groups are identified by a combination of synapomorphies and symplesiomorphies . If many subgroups are missing from
532-482: 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 ,
570-503: 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
608-569: 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
646-1745: The Middle Devonian period . After Benton, 2004; and Swartz, 2012. Other clades include the Eotetrapodiformes ( Tinirau , Platycephalichthys , the Tristichopteridae and Elpistostegalia ). Older taxa which include late stem tetrapods and early tetrapods are the Labyrinthodontia and Ichthyostegalia . The cladogram is based on a phylogenetic analysis of 46 taxa using 204 characters by B. Swartz in 2012. † Kenichthys † Rhizodontidae [REDACTED] † Marsdenichthys † Canowindra † Koharalepis † Beelarongia † Gogonasus [REDACTED] † Gyroptychius † Osteolepis [REDACTED] † Medoevia † Megalichthyidae [REDACTED] † Spodichthys † Tristichopterus † Eusthenopteron [REDACTED] † Jarvikina † Cabonnichthys † Mandageria † Eusthenodon [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 ( crown group ) [REDACTED] The following cladogram follows
684-638: 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
722-531: The cosmine layer found in more primitive tetrapodomorphs. Most of the body was covered in round, overlapping elasmoid scales with a median projection on the inner side. Thicker, enlarged scales occurred on the bases of the fins. The earliest-known fossilised evidence of bone marrow has been found in Eusthenopteron, which may be the origin of bone marrow in tetrapods. The ontogeny of the Tristichopteridae
760-408: The crown group tetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of early stem tetrapods , which includes several groups of related lobe-finned fishes, collectively known as the osteolepiforms . The Tetrapodomorpha minus the crown group Tetrapoda are the stem Tetrapoda , a paraphyletic unit encompassing the fish to tetrapod transition. Among
798-486: The end of the Late Devonian . The Tristichopteridae were medium-sized ( Tristichopterus , 30 cm) to very large animals. The smallest forms (such as Tristichopterus ) attained lengths of 30 cm, and the largest forms ( Hyneria ) could grow several meters long, possessed teeth up to 5 cm long, and were the largest predators in their faunal communities. Tristichopterids had a strongly developed fin skeleton. In
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#1732859431028836-454: The characteristics defining tetrapodomorphs are modifications to the fins, notably a humerus with convex head articulating with the glenoid fossa (the socket of the shoulder joint). Another key trait is the internal nostril or choana . Most fish have two pairs of nostrils, one on either side of the head for incoming water (incurrent nostrils) and another pair for outgoing water (excurrent nostrils). In early tetrapodomorphs like Kenichthys ,
874-450: 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
912-561: The excurrent nostrils had shifted towards the mouth's perimeter. In later tetrapodomorphs, including tetrapods, the excurrent nostril is positioned inside the mouth, where it is known as the choana . The nearly-equivalent clade Choanata often refers to these later forms specifically. Tetrapodomorph fossils are known from the early Devonian onwards, and include Osteolepis , Panderichthys , Kenichthys and Tungsenia . Tetrapodomorpha evolved from ancient lobe-finned fish ( sarcopterygians ) around 390 million years ago in
950-473: The fact that a monophyletic group includes organisms consisting of all 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
988-422: The features of the elpistostegalians , a diverse clade of tetrapodomorphs close to the origin of (and including) tetrapods. This mainly concerns the shape of the skull and a reduction in size of the posterior fins. An old and persistent notion is that Eusthenopteron was able to crawl onto land using its fins. However, there is no evidence actually supporting this idea. All tristichopterids had become extinct by
1026-477: The hatchling already attaining the general body form of the adult. The family Tristichopteridae was named by Edward Drinker Cope in 1889, who established it as the sole family of the order Rhipidistia . In turn, Cope deemed Rhipidistia and Actinistia as the two orders forming a superorder he named Rhipidopterygia. In 1955, Lev Berg erected a family named Eusthenopteridae to include the genera Tristichopterus and Eusthenopteron , and placed this family within
1064-605: 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
1102-412: The major bones of the hind legs, femur, tibia, and fibula. Ankle bones (tarsal bones) and toes cannot yet be identified. The limbs were oriented to the side and could only be moved back and forth about 20 to 25°. The anal fin sat on a basal, fleshy peduncle. The caudal fin possessed three lobes, initially asymmetrical in basal forms and becoming more symmetrical externally in later forms. The scales lacked
1140-568: 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 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
1178-464: The order Rhizodontiformes . More genera would later be placed in Eusthenopteridae, with Vorobyeva and Obruchev (1964) stating Eusthenodon and possibly Platycephalichthys are members of this family, while Carroll (1988) added Hyneria and tentatively assigned Devonosteus and Litoptychus to the group. Currently, Eusthenopteridae is deemed a junior synonym of Tristichopteridae. In
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1216-760: The past, Tristichopteridae was assigned to the order Osteolepiformes , a group of tetrapodomorphs that is now considered paraphyletic . The following phylogeny is modified from Schwartz (2012). Here, Platycephalichthys is not considered a member of the Tristichopteridae: Spodichthys Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Mandageria Eusthenodon [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Tetrapodomorph See also below . Tetrapodomorpha (also known as Choanata )
1254-675: 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
1292-408: The results found by Clement et al . (2021). Dipnomorpha Kenichthys Tungsenia Hongyu Gooloogongia [REDACTED] Sauripterus Barameda Screbinodus Rhizodus Paraphyletic Paraphyly 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
1330-563: 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
1368-400: The skeleton of the front fins, which were deeply attached, the elements of the forelimb of the later tetrapodomorphs, such as the humerus, ulna and radius, can already be recognized. The parts of the bones directed outward from the body trunk were flattened. The pelvis had long, tapering pubic branches (pubic rami) that possibly met in a cartilaginous symphysis. The ventral fins also contained
1406-460: The status of "groups", nor does it reify them with explanations, as in cladistics they are not seen as 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
1444-477: The two Ancient Greek words παρά ( pará ), meaning "beside, near", and φῦλον ( phûlon ), meaning "genus, species", and refers to 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
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