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  Phylogeny (Greek, ‘evolution of types’), in the life sciences, is the history of a living organism in terms of its evolution. It provides the basis for phyletic taxonomy. Phylogeny is usually very incomplete due to the fragmentary nature of the fossil record and the more than three billion years over which evolution has occurred. Evidence for phylogenetic relationships was traditionally derived from comparative palaeontology, anatomy and embryology, but these days it is supplemented with data from biochemists and molecular biologists. A phylogenetic logenetic tree (dendrogram) is used to order species taxonomically, with the species placed at the tips of the branches and the common ancestor represented by the trunk. The distances between species on the tree indicate closeness of relationship in evolutionary terms, though this can be difficult to determine unambiguously. The linking of species with their ancestors in such a rigid (cladistic) fashion can cause taxonomic problems: for example, on a strict phylogenetic tree, crocodiles are separated from lizards as they have a more recent bird ancestor than they do a lizard ancestor. However, crocodiles and lizards are grouped together as reptiles when they are classified according to appearance (phenetic classification). RB

See also anatomy; morphology.Further reading Martin Rudwick, The Meaning of Fossils.



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Other Terms : Cliometrics | Object Relations | Uncertainty Principle
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