Reptilia (green field) is a paraphyletic group comprising all amniotes (Amniota) except for two subgroups: Mammalia (mammals) and Aves (birds); therefore, Reptilia is not a clade. In contrast, Amniota itself is a clade, which is a monophyletic group.

In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—monophyletic subgroups. The group is said to be paraphyletic with respect to the excluded subgroups. The term is commonly used in phylogenetics (a subfield of biology) and in linguistics.

The term was coined to apply to well-known taxa like reptiles (Reptilia) which, as commonly named and traditionally defined, is paraphyletic with respect to mammals and birds. Reptilia contains the last common ancestor of reptiles and all descendants of that ancestor—including all extant reptiles as well as the extinct synapsids—except for mammals and birds. Other commonly recognized paraphyletic groups include fish, monkeys and lizards.[1]

If many subgroups are missing from the named group, it is said to be polyparaphyletic. A paraphyletic group cannot be a clade, which is a monophyletic group.


Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly (the prosimians, in blue, including the red patch), and a polyphyly (the night-active primates, the lorises and the tarsiers, in red).

Relation to monophyletic groups

Groups that include all the descendants of a common ancestor are said to be monophyletic. A paraphyletic group is a monophyletic group from which one or more subsidiary clades (monophyletic groups) is excluded to form a separate group. Ereshefsky has argued that paraphyletic taxa are the result of anagenesis in the excluded group or groups.[2] For example, dinosaurs are paraphyletic with respect to birds because birds possess many features that dinosaurs lack and occupy a distinctive niche.

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.

These terms were developed during the debates of the 1960s and 70s accompanying the rise of cladistics.

Examples of paraphyletic groups

Wasps are paraphyletic, consisting of the clade Apocrita without ants and bees, which are not usually considered to be wasps.
Paraphyletic taxon Excluded clades Corresponding monophyletic taxon
Prokaryotes[10] Eukaryota[10] Cellular organisms
Protista Animalia, Plantae, and Fungi Eukaryota
Bryophytes Tracheophytes Embryophyta
Charophyta Embryophyta (Land plants) Streptophyta
Gymnosperms Angiospermae Spermatophyta
Dicotyledons[5] Monocotyledoneae Angiospermae (Flowering plant)
Invertebrates Vertebrata Animalia
Vertebrata Myxini Craniata[note 2]
Monkeys Hominoidea Simiiformes
Prosimians Simiiformes Primates
Pongidae (Great-apes) Hominina Hominidae[note 3]
Ape Hominina Hominoidea[note 4]
Even-toed ungulates[11] Cetacea Cetartiodactyla[12]
Pelycosaurs Therapsida Synapsida
Plagiaulacidans[13] Cimolodonta, Arginbaataridae Multituberculata
Reptiles[14]Mammals, Birds[14] Amniota
Lizard Snakes Squamates
Fish Tetrapoda Vertebrate
Wasps Ants, Bees Apocrita
Bony fish[8] Tetrapoda[8] Euteleostomi
Nautiloidea Ammonoidea, Coleoidea Cephalopoda[note 5]
Crustaceans[15][16] Hexapoda[15][16] Tetraconata

Paraphyly in species

Main article: Paraspecies

Species have a special status in systematics as being an observable feature of nature itself and as the basic unit of classification.[17] The phylogenetic species concept requires species to be monophyletic, but paraphyletic species are common in nature. Paraphyly is common in speciation, whereby a mother species (a paraspecies) gives rise to a daughter species without itself becoming extinct.[18] Research indicates as many as 20 percent of all animal species and between 20 and 50 percent of plant species are paraphyletic.[19][20] Accounting for these facts, some taxonomists argue that paraphyly is a trait of nature that should be acknowledged at higher taxonomic levels.[21][22] Others argue to retain monophyly only in higher taxa, but that the special status of species should excuse them from the monophyly prerequisite.

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 Neogene evolution of the Artiodactyla (even-toed ungulates, like deer) has taken place in an environment so different from that of 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 excludes many of its descendant organisms (the eukaryotes), but it is very useful because it has a clearly defined and significant distinction (absence of a cell nucleus, a plesiomorphy) from its excluded descendants.

Also, paraphyletic groups are involved in evolutionary transitions, the development of the first tetrapods from their ancestors for example. Any name given to these ancestors to distinguish them from tetrapods—"fish", for example—necessarily picks out a paraphyletic group, because the descendant tetrapods are not included.[23]

The term "evolutionary grade" is sometimes used for paraphyletic groups.[24]

Independently evolved traits

Vivipary, the production of offspring without the laying of a fertilized egg, developed independently in the lineages that led to humans (Homo sapiens) and southern water skinks (Eulampus tympanum, a kind of lizard). Put another way, at least one of the lineages that led to these species from their last common ancestor contains nonviviparous animals, the pelycosaurs ancestral to mammals; vivipary appeared subsequently in the mammal lineage.

Independently-developed traits like these cannot be used to distinguish paraphyletic groups because paraphyly requires the excluded groups to be monophyletic. Pelycosaurs were descended from the last common ancestor of skinks and humans, so vivipary could be paraphyletic only if the pelycosaurs were part of an excluded monophyletic group. Because this group is monophyletic, it contains all descendents of the pelycosaurs; because it is excluded, it contains no viviparous animals. This does not work, because humans are among these descendents. Vivipary in a group that includes humans and skinks cannot be paraphyletic.

Not paraphyly


Main article: Tree model

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 it refers to the nine branches of the Austronesian family that are not Malayo-Polynesian and restricted to the island of Taiwan.[27]


  1. The history of flowering plant classification can be found under History of the classification of flowering plants.
  2. Myxini is sometimes included in vertebrata, though the members have no vertebral column.
  3. Hominina is sometimes included in Great Ape.
  4. Hominina is sometimes included in Ape.
  5. Paraphyly is disputed. See Lindgren (2004) at

See also


  1. Romer, A.S. (1949): The Vertebrate Body. W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970)
  2. Handbook of Plant Science.
  3. Sapp, Jan (June 2005). "The prokaryote–eukaryote dichotomy: meanings and mythology". Microbiology and Molecular Biology Reviews. 69 (2): 292–305. doi:10.1128/MMBR.69.2.292-305.2005. PMC 1197417Freely accessible. PMID 15944457.
  4. Stackebrabdt, E.; Tindell, B.; Ludwig, W.; Goodfellow, M. (1999). "Prokaryotic Diversity and Systematics". In Lengeler, Joseph W.; Drews, Gerhart; Schlegel, Hans Günter. Biology of the prokaryotes. Stuttgart: Georg Thieme Verlag. p. 679.
  5. 1 2 Simpson 2006, pp. 139–140. "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 ...."
  6. O'Leary, Maureen A. (2001). "The phylogenetic position of cetaceans: further combined data analyses, comparisons with the stratigraphic record and a discussion of character optimization". American Zoologist. 41 (3): 487–506. doi:10.1093/icb/41.3.487.
  7. Romer, A. S. & Parsons, T. S. (1985): The Vertebrate Body. (6th ed.) Saunders, Philadelphia.
  8. 1 2 3 A Tree of Life
  9. Johnson, Brian R.; Borowiec, Marek L.; Chiu, Joanna C.; Lee, Ernest K.; Atallah, Joel; Ward, Philip S. (2013). "Phylogenomics Resolves Evolutionary Relationships among Ants, Bees, and Wasps" (PDF). Current Biology. 23 (20): 2058–2062. doi:10.1016/j.cub.2013.08.050. PMID 24094856.
  10. 1 2 Berg, Linda (2008). Introductory Botany: Plants, People, and the Environment (2nd ed.). Belmont CA: Thomson Corporation. p. 360. ISBN 0-03-075453-4.
  11. O'Leary, Maureen A. (2001). "The Phylogenetic Position of Cetaceans: Further Combined Data Analyses, Comparisons with the Stratigraphic Record and a Discussion of Character Optimization". American Zoologist. 41 (3): 487–506. doi:10.1093/icb/41.3.487.
  12. Savage, R. J. G. & Long, M. R. (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. p. 208. ISBN 0-8160-1194-X.
  13. Kielan-Jaworowska, Z. & Hurum, J. (2001). "Phylogeny and Systematics of Multituberculate Animals". Palaeontology. 44 (3): 389–429. doi:10.1111/1475-4983.00185.
  14. 1 2 Tudge, Colin (2000). The Variety of Life. Oxford University Press. ISBN 0198604262.
  15. 1 2 David R. Andrew (2011). "A new view of insect–crustacean relationships II. Inferences from expressed sequence tags and comparisons with neural cladistics". Arthropod Structure & Development. 40 (3): 289–302. doi:10.1016/j.asd.2011.02.001.
  16. 1 2 Bjoern, M.; von Reumont, Ronald A.; Jenner, Matthew A.; Wills, Emiliano; Dell'Ampio, Günther; Pass, Ingo; Ebersberger, Benjamin; Meyer, Stefan; Koenemann, Thomas M. Iliffe (2012). "Pancrustacean phylogeny in the light of new phylogenomic data: support for Remipedia as the possible sister group of Hexapoda" (PDF proofs). Molecular Biology and Evolution. 29 (3): 1031–1045. doi:10.1093/molbev/msr270. PMID 22049065.
  17. Queiroz, Kevin; Donoghue, Michael J. (December 1988). "Phylogenetic Systematics and the Species Problem". Cladistics. 4 (4): 317–338. doi:10.1111/j.1096-0031.1988.tb00518.x. Retrieved 21 January 2015.
  18. James S. Albert; Roberto E. Reis (8 March 2011). Historical Biogeography of Neotropical Freshwater Fishes. University of California Press. p. 308. Retrieved 28 June 2011.
  19. Ross, Howard A. (July 2014). "The incidence of species-level paraphyly in animals: A re-assessment". Molecular Phylogenetics and Evolution. 76: 10–17. doi:10.1016/j.ympev.2014.02.021.
  20. Crisp, M.D,; Chandler, G.T. (1 July 1996). "Paraphyletic species". Telopea. 6 (4): 813–844. doi:10.7751/telopea19963037. Retrieved 22 January 2015.
  21. Zander, Richard (2013). Framework for Post-Phylogenetic Systematics. St. Louis: Zetetic Publications, Amazon CreateSpace.
  22. Aubert, D. 2015. A formal analysis of phylogenetic terminology: Towards a reconsideration of the current paradigm in systematics. Phytoneuron 2015-66:1–54.
  23. Kazlev, M.A. & White, T. "Amphibians, Systematics, and Cladistics". Palaeos website. Retrieved 16 August 2012.
  24. Dawkins, Richard (2004). "Mammal-like Reptiles". The Ancestor's Tale, A Pilgrimage to the Dawn of Life. Boston: Houghton Mifflin Company. ISBN 0-618-00583-8.
  25. Kutschera, Ulrich; Elliott, J Malcolm (26 March 2013). "Do mudskippers and lungfishes elucidate the early evolution of four-limbed vertebrates?". Evolution: Education and Outreach. 6 (8). doi:10.1186/1936-6434-6-8.
  26. Harshman, John; Braun, Edward L.; et al. (2 September 2008). "Phylogenomic evidence for multiple losses of flight in ratite birds". PNAS. 105 (36): 13462–13467. doi:10.1073/pnas.0803242105. PMC 2533212Freely accessible. PMID 18765814.
  27. 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.


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