In phylogenetics, a group of organisms is said to be paraphyletic (Greek para = near and phyle = race) if the group contains its most recent common ancestor but does not contain all the descendants of that ancestor. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly In Genetics, the most recent common ancestor ( MRCA) of any set of Organisms is the most recent individual from which all organisms in the group are directly A group of organisms is said to have common descent if they have a common Ancestor. An ancestor is a Parent or ( recursively) the parent of an ancestor (i

Relation to monophyletic groups

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

Groups that do include all the descendants of the most recent common ancestor are said to be monophyletic. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor A paraphyletic group is a monophyletic group from which one or more of the clades is excluded to form a separate group (as in the paradigmatic example of reptiles and birds, shown in the picture). A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor

A group that does not contain the most recent common ancestor of its members is said to be polyphyletic (Greek polys = many). In Phylogenetics, a Taxon is polyphyletic ( Greek for "of many races" if the trait its members have in common evolved separately in different

These terms were developed during the debates of the 1960s and 70s accompanying the rise of cladistics (a clade is a term for a monophyletic group). Cladistics is the hierarchical classification of Species based on evolutionary ancestry Before that period the distinction between mono- and polyphyletic groups was based on the inclusion or exclusion of the most recent common ancestor. It was shown, however, that the inclusion of ancestors in the classification leads to unavoidable logical inconsistencies, and, in some schools of taxonomy, the phylogenetic pattern is described exclusively in terms of nested patterns of the sister group relationships between the known representatives of taxa without referring to the ancestor-descendant relationships. Cladistics is the hierarchical classification of Species based on evolutionary ancestry

Examples of paraphyletic groups

Many of the older classifications contain paraphyletic groups, especially the traditional 2–6 kingdom systems and the classic division of the vertebrates. In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Paraphyletic groups are often erected on the basis of (sym)-plesiomorphies (ancestral similarities) instead of (syn)apomorphies (derived similarities). Examples of well-known paraphyletic groups includes:

• In the flowering plants, Dicotyledonae, in the traditional sense, because they exclude Monocotyledonae. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Dicotyledons, or "dicots", is a name for a group of Flowering plants whose Seed typically has two embryonic leaves or Cotyledons There Monocotyledons or monocots are one of two major groups of Flowering plants (angiosperms that are traditionally recognised the other being Dicotyledons

• The order Artiodactyla (Even-toed ungulates), because it excludes Cetaceans (whales, dolphins, etc). The even-toed ungulates form the Mammal order Artiodactyla. They are Ungulates whose weight is borne (if they have more than two toes about The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is

• The class Reptilia as traditionally defined is paraphyletic because that class excludes birds (class Aves), which are descended from reptiles (see the illustration above). Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Reptiles would be monophyletic if Reptiles were defined to include Aves.

• The Prokaryotes (organisms without cell nuclei) consisting of bacteria and archaea, which is paraphyletic, because the clade containing the prokaryotes also includes all eukaryotes (organisms with cell nuclei). The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor This is because the root of the tree of life, the last universal common ancestor (LUCA), is believed to lie between Archaea and Bacteria. Archaea and Eukaryota are thought to share a more recent common ancestor.

• Agnatha, jawless fish. Agnatha ( Greek, "no jaws" is a Paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata This group contains two significant animal groups, hagfish and lampreys. Hagfish are marine Craniates of the class Myxini, also known as Hyperotreti. A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth yet their nearest common ancestor is the ancestor of all vertebrates, so Agnatha is paraphyletic.

• Osteichthyes, bony fish, are paraphyletic^[1] because they include Actinopterygii (ray-finned fish) and Sarcopterygii (lungfish, etc). Osteichthyes (ˌɒstiːˈɪkθiːz also called bony fish, are a taxonomic Class of Fish that includes the ray-finned fish ( Actinopterygii The Actinopterygii (the plural form of Actinopterygius) comprise the class of the ray-finned fishes. Sarcopterygii (from Greek σαρξ sarx, flesh and πτερυξ pteryx, fin is traditionally the class of lobe-finned Fishes consisting However, tetrapods are descendents of the nearest common ancestor of Actinopterygii and Sarcopterygii, and tetrapods are not in Osteichthyes, hence Osteichthyes is paraphyletic. Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals

• Porifera - Now divided into Siliceous Sponges and Calcareous sponges, which together are not monophyletic. The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals

• Invertebrates are defined as all animals other than vertebrates, which makes it a paraphyletic group. An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes

The term paraphyly may be used in any system in which genetic descent modeled by trees is useful. For instance, in linguistics, the Formosan languages form a paraphyletic group of the Austronesian languages as the term refers to the nine branches of the Autronesian family that are not Malayo-Polynesian and restricted to the island of Taiwan. Linguistics is the scientific study of Language, encompassing a number of sub-fields The Malayo-Polynesian languages are a subgroup of the Austronesian languages, with approximately 351 million speakers Taiwan ( Taiwanese: Tâi-oân/Tāi-oân (historically 大灣/台員/大員/台圓/大圓/台窩灣 is an Island in East Asia.

Cladistics generally discourage paraphyletic groups

In most cladistics-based schools of taxonomy, the existence of paraphyletic groups (as well as polyphyletic groups) in a classification is discouraged. Cladistics is the hierarchical classification of Species based on evolutionary ancestry Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos In Phylogenetics, a Taxon is polyphyletic ( Greek for "of many races" if the trait its members have in common evolved separately in different Monophyletic groups (that is, clades) are considered by these schools of thought to be the most important grouping of organisims, for the following reaons:

• Clades are simple to define: a typical clade definition is "All descendents of the nearest common ancestor of species X and Y". A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor On the other hand, polyphyletic and paraphyletic groups are always defined in terms of clades, for example "reptiles are the Sauropsid clade, minus the Aves clade". Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Or "Warm-blooded animals are the Aves clade plus the Mammals clade". Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Because polyphyletic and paraphyletic groups are defined in terms of clades, they are considered less important than clades.

• For a given evolutionary tree of, say, N nodes, there are exactly N clades (one per node). However, the number of paraphyletic groups and polyphyletic groups is exponentially larger than that, on the order of 2^N. Yet only a small fraction of the paraphyletic groups are given names or discussed.

• Paraphyletic groups often have their origin in traditional taxonomy, based on similar morphological characteristics. The original perception may have been that the group was entirely descended from a single ancestor. If such a group is later discovered (for instance, due to convergent evolution) to be paraphyletic, rather than monophyletic, then such a group loses its original significance. Convergent evolution describes the acquisition of the same biological trait in unrelated lineages

Uses for paraphyletic groups

Others argue that paraphyletic groups are necessary for a comprehensive classification including extinct groups, since each species, genus, and so forth necessarily originates from part of another.

For instance, the Prokaryote group is paraphyletic because it excludes many of its descendent organisms (such as Eukaryotes), yet the Prokaryote group is very useful because it has a clearly-defined and significant distinction (no cell nucleus) from its excluded descendents. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex So, even though Prokaryotes are not a clade, the term is still useful.

It has been suggested that paraphyletic groups be clearly marked to distinguish them from clades, for instance with asterisks: Reptilia*. Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers The term evolutionary grade is sometimes used for such groups. ^[2]

References

Cited

General

• Colin Tudge (2000). Colin Tudge (born 22 April 1943) is a British science writer A biologist by training he is the author of numerous works on food agriculture genetics 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. The Variety of Life. Oxford University Press. ISBN 0198604262.