Evolutionary taxonomy

Evolutionary taxonomy classifies organisms using both common ancestry and the amount of evolutionary change they have undergone. It permits groups that do not include every descendant of a common ancestor when their members share distinctive adaptations.

Cladistics: A method of classification that groups organisms by shared derived traits and common ancestry. Unlike evolutionary taxonomy, cladistics requires each named group to include an ancestor and all its descendants.
Phylogenetics: The study of evolutionary relationships among organisms or other biological entities. Phylogenetic hypotheses supply the ancestry component of evolutionary classifications.
Julian Huxley: An English biologist who synthesized evolutionary theory and popularized the term evolutionary synthesis. His evolutionary synthesis helped shape the framework in which evolutionary taxonomy developed.
Reptilia: A traditional vertebrate group including turtles, lizards, snakes, and crocodilians, but excluding birds. Traditional Reptilia illustrates a familiar paraphyletic group retained for its recognizable evolutionary grade.
Phenetics: A classification approach that groups organisms by overall similarity, without prioritizing evolutionary history. Its similarity-based groupings show what classification looks like without evolutionary taxonomy's historical criteria.
Evolutionary grade: A group of organisms at a comparable level of evolutionary organization, often defined by shared adaptations. Grades let evolutionary taxonomy recognize similar levels of adaptation even when groups exclude descendants.
George Gaylord Simpson: An American paleontologist who integrated fossil evidence with modern evolutionary theory. Simpson articulated influential principles for classifying organisms by both phylogeny and degree of difference.
Aves: The vertebrate class comprising birds, descended from theropod dinosaurs. Birds reveal the classification dispute: whether to include them within reptiles or treat them as a distinct group.
Phylogenetic nomenclature: A system for naming taxa by explicitly defining them through evolutionary relationships. It links names directly to ancestry rather than balancing ancestry against degree of change.
Paraphyly: The condition of a group containing a common ancestor but not all of its descendants. Paraphyletic groups can represent distinctive evolutionary grades in this approach.

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