systematics phylogenetics phylogenetic diagram cladistics shared character derived character clade cladogram

www.scilinks.org Topic: Phylogenetic Tree Keyword: HM61141

Maintained by the

www.scilinks.org Topic: Phylogenetic Tree Keyword: HM61141

Maintained by the riiL National Science ti\n J5. Teachers Association

Word Roots and Origins clade from the Greek klados, meaning "a branch" or "a shoot"

Systematists also compare homologous features, items that share a common ancestry. For example, the jaws of pangolins and of dogs are homologous. It is essential to separate homologous features from analogous features (features that are similar because they have a similar function rather than a similar lineage). Scales are an example of analogous features. Both pangolins and snakes have scales, but the fossil record shows that scales evolved independently in the two taxa. The greater the number of homologous features shared by two organisms, the more closely related the organisms are.

Embryological evidence also helps establish phylogenetic relationships. For example, a fluid-filled sac called an amnion surrounds the embryos of reptiles, birds, and mammals. The embryos of other vertebrates lack an amnion. This shared and homologous embryological feature is used to define amniotes. All amniotes are combined into one taxon that includes all reptiles, birds, and mammals but excludes other vertebrates.

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