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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 is said to be paraphyletic with respect to the excluded subgroups. In contrast, a grouping (a ) includes a common ancestor and all of its descendants.

The terms are commonly used in (a subfield of ) and in the of historical linguistics. Paraphyletic groups are identified by a combination of synapomorphies and . 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 , having been coined by zoologist to apply to well-known taxa like Reptilia (), which is paraphyletic with respect to . Reptilia contains the last common ancestor of reptiles and all descendants of that ancestor except for birds. Other commonly recognized paraphyletic groups include , , and .


Etymology
The term paraphyly, or paraphyletic, derives from the two words (), meaning "beside, near", and (), meaning "genus, species",
(1981). 9782010035289, Hachette.
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 , or monophyletic, builds on the Ancient Greek prefix (), meaning "alone, only, unique", and refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor.

By comparison, the term , or polyphyletic, uses the Ancient Greek prefix (), meaning "many, a lot of", and refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources.


Phylogenetics

In cladistics
Groups that include all the descendants of a common ancestor are said to be . A paraphyletic group is a monophyletic group from which one or more subsidiary (monophyletic groups) are excluded to form a separate group. Philosopher of science Marc Ereshefsky has argued that paraphyletic taxa are the result of in the excluded group or groups.
(2007). 9780470057230, John Wiley & Sons. .
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 the actual products of evolutionary events.
(2020). 9781108882675, Cambridge University Press.

A group whose identifying features evolved convergently in two or more lineages is (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 the debates of the 1960s and 1970s accompanying the rise of .

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.

(2025). 9789400723351, Springer. .
Related terms are stem group, , budding cladogenesis, anagenesis, or 'grade' groupings. Paraphyletic groups are often relics from outdated hypotheses of phylogenic relationships from before the rise of cladistics.


Examples
The (single-celled life forms without cell nuclei) are a paraphyletic grouping, because they exclude the , a descendant group. and are prokaryotes, but archaea and eukaryotes share a common ancestor that is not ancestral to the bacteria. The prokaryote/eukaryote distinction was proposed by 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 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, (in the traditional sense) are paraphyletic because the group excludes . "Dicotyledon" has not been used as a botanic classification for decades, but is allowed as a synonym of Magnoliopsida.The history of flowering plant classification can be found under History of the classification of flowering plants. Phylogenetic analysis indicates that the are a development from a ancestor. Excluding monocots from the dicots makes the latter a paraphyletic group.. "It is now thought that the possession of two cotyledons is an ancestral feature for the taxa of the flowering plants and not an apomorphy for any group within. The 'dicots' ... are paraphyletic ...."

Among animals, several familiar groups are not, in fact, clades. The order (even-toed ungulates) as traditionally defined is paraphyletic because it excludes (whales, dolphins, etc.). Under the ranks of the , 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 is paraphyletic because it excludes birds (class ). Under a traditional classification, these two taxa are separate classes. However birds are sister taxon to a group of dinosaurs (part of ), both of which are "reptiles". & Parsons, T. S. (1985): The Vertebrate Body. (6th ed.) Saunders, Philadelphia.

, bony fish, are paraphyletic when circumscribed to include only (ray-finned fish) and (lungfish, etc.), and to exclude ; more recently, Osteichthyes is treated as a clade, including the tetrapods.

The "" are paraphyletic, consisting of the narrow-waisted without the and . The sawflies () are similarly paraphyletic, forming all of the except for the Apocrita, a clade deep within the sawfly tree. are not a clade because the (insects) are excluded. The modern clade that spans all of them is the .

One of the goals of modern taxonomy over the past fifty years has been to eliminate paraphyletic taxa from formal classifications.Schuh, Randall T. "The Linnaean system and its 250-year persistence." The Botanical Review 69, no. 1 (2003): 59. Below is a partial list of obsolete taxa and informal groups that have been found to be paraphyletic.

(2025). 9780030754531, Thomson Corporation.
,
(2013). 9780486151359, Courier. .
Tree of life web project – Chordates .
(2025). 9780632056378, Blackwell Science.
(1986). 081601194X, Facts on File. . 081601194X
Parasitic Hymenoptera (Parasitica). RL Zuparko, Encyclopedia of Entomology, 2004
(2025). 9780030259821, . .
|
, ,
(2025). 9780801882210, Johns Hopkins University Press. .
, p. 699.


Paraphyly in 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 a "single common ancestor" organism. Paraphyly is common in , whereby a mother species (a ) gives rise to a daughter species without itself becoming extinct.
(2011). 9780520268685, University of California Press. .
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 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.

(2025). 9781501752773, Cornell University Press.
They consider Zander's extension of the "paraphyletic species" argument to higher taxa to represent a


Uses for paraphyletic groups
When the appearance of significant traits has led a subclade on an evolutionary path very divergent from that of a more inclusive clade, it often makes sense to study the paraphyletic group that remains without considering the larger clade. For example, the evolution of the Artiodactyla (even-toed ungulates, like deer, cows, pigs and hippopotamuses - , , and , the families that contain these various artiodactyls, are all monophyletic groups) has taken place in environments so different from that of the (whales, dolphins, and porpoises) that the Artiodactyla are often studied in isolation even though the cetaceans are a descendant group. The group is another example; it is paraphyletic because it is composed of two Domains (Eubacteria and Archaea) and excludes (the ). It is very useful because it has a clearly defined and significant distinction (absence of a cell nucleus, a ) 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" is sometimes used for paraphyletic groups.

(2025). 9780618005833, Houghton Mifflin.
Moreover, the concepts of , paraphyly, and have been used in deducing key genes for of diverse group of species.


Linguistics
The concept of paraphyly has also been applied to historical linguistics, where the methods of 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 the island of .Greenhill, Simon J. and Russell D. Gray. (2009.) "Austronesian Language and Phylogenies: Myths and Misconceptions About Bayesian Computational Methods", in Austronesian Historical Linguistics and Culture History: a Festschrift for Robert Blust, edited by Alexander Adelaar and Andrew Pawley. Canberra: Pacific Linguistics, Research School of Pacific and Asian Studies, The Australian National University.


See also


Explanatory notes

Bibliography


External links
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