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In phylogenetics, a grouping of organisms is said to be paraphyletic (Greek para = near and phyle = race) if all the members of the group have a common ancestor, but the group does not include all the descendants of the most recent common ancestor of all group members. In biology, Phylogenetics (Greek: phylon = race and genetic = birth) is the taxonomical classification of organisms based on how closely they are related in terms of evolutionary differences. ... An ancestor is a parent or (recursively) the parent of an ancestor. ...

Reptiles are a paraphyletic group. The group can be made monophyletic by including the birds (aves).

Groups which include all the descendants of the most recent common ancestor are commonly termed monophyletic or holophyletic. The former is more common, but sometimes paraphyletic groups are also considered monophyletic, in which case the latter is used. A paraphyletic group can be fixed by expanding it, and including other clades. A class which is descended from more than one root form is called polyphyletic. Image:Paraphyletic. ... Image:Paraphyletic. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ... In biology, a taxon is polyphyletic if it is descended from more than one root form (in Greek poly = many and phyletic = racial). ...

Many of the older classifications contain paraphyletic groups, especially the traditional 2-6 kingdom systems and the classic division of the vertebrates. For example, the class Reptilia as traditionally defined is paraphyletic because that class does not include two groups of its descendants, birds (in class Aves, birds), and mammals (in class Mammalia). Paraphyletic groups are often erected on the basis of plesiomorphies (ancestral similarities) instead of upon apomorphies (derived similarities). In biology, a kingdom or regnum is the top-level, or nearly the top-level, taxon of organisms in scientific classification. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Orders  Crocodylia - Crocodilians  Rhynchocephalia - Tuataras  Squamata   Suborder Sauria - Lizards   Suborder Serpentes - Snakes Testudines - Turtles Superorder Dinosauria  Saurischia  Ornithischia The reptiles are a group of vertebrate animals. ... For other meanings of bird, see bird (disambiguation). ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals characterized by the presence of mammary glands...

In most cladistics-based schools of taxonomy, the existence of paraphyletic groups in a classification are regarded as errors. Some groups in currently accepted taxonomies may later turn out to be paraphyletic, in which case the classifications may be revised to eliminate them. Some, however, feel that having paraphyletic groups is an acceptable sacrifice if it makes the taxonomy more understandable. Others argue that paraphyletic groups are necessary to have a comprehensive classification including extinct groups, since each species, genus, and so forth necessarily originates from part of another. It has been suggested that paraphyletic groups should be allowed but clearly marked as such, for instance in the form Reptilia*. Greek clados = branch) or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. ...

The term paraphyletic is also used in historical linguistics, with similar meaning. For example, centum and satem are paraphyletic groups of Indo-European languages. Historical linguistics (also diachronic linguistics or comparative linguistics) is primarily the study of the ways in which languages change over time, by means of examining languages which are recognizably related through similarities such as vocabulary, word formation, and syntax, as well as the surviving records of ancient languages. ... Centum is the collective name for the branches of Indo-European in which the so-called Satem shift, the change of palato-velar *k^, *g^, *g^h into fricatives or affricates, did not take place, and the palato-velar consonants merged with plain velars (*k, *g, *gh). ... The Satem division of the Indo-European family includes the following branches: Indo-Iranian, Baltic and Slavic, Armenian, Albanian, perhaps also a number of barely documented extinct languages, such as Thracian (see: Indo-European languages). ... The Indo-European languages include some 443 (SIL estimate) languages and dialects spoken by about three billion people, including most of the major language families of Europe and western Asia, which belong to a single superfamily. ...

References

• Colin Tudge (2000). The Variety of Life. Oxford University Press. ISBN 0198604262.