Editing Transitional fossil (section)

===Transitions in phylogenetic nomenclature===
{{Main|Phylogenetic nomenclature}}
{{See also|Evolutionary taxonomy}}
[[File:Spindle diagram.jpg|thumb|left|Traditional spindle diagram showing the [[vertebrate]]s classes "budding" off from each other. Transitional fossils typically represent animals from near the branching points.]]
In evolutionary taxonomy, the prevailing form of [[Taxonomy (biology)|taxonomy]] during much of the 20th century and still used in non-specialist textbooks, [[Taxon|taxa]] based on morphological similarity are often drawn as "bubbles" or "spindles" branching off from each other, forming evolutionary trees.<ref>For example, see {{harvnb|Benton|1997}}</ref> Transitional forms are seen as falling between the various groups in terms of anatomy, having a mixture of characteristics from inside and outside the newly branched [[clade]].{{sfn|Prothero|2007|p=[https://archive.org/details/evolutionwhatfos00prot_0/page/84 84]}}

With the establishment of [[cladistics]] in the 1990s, relationships commonly came to be expressed in [[cladogram]]s that illustrate the branching of the evolutionary lineages in stick-like figures. The different so-called "natural" or "[[Monophyly|monophyletic]]" groups form nested units, and only these are given [[phylogenetic nomenclature|phylogenetic names]]. While in traditional classification tetrapods and fish are seen as two different groups, phylogenetically tetrapods are considered a branch of fish. Thus, with cladistics there is no longer a transition between established groups, and the term "transitional fossils" is a [[misnomer]]. Differentiation occurs within groups, represented as branches in the cladogram.<ref name="Palaeos">{{cite web |url=http://palaeos.com/vertebrates/tetrapoda/amphibians.html |title=Amphibians, Systematics, and Cladistics |last=Kazlev |first=M. Alan |website=[[Palaeos]] |access-date=2012-05-09}}</ref>

In a cladistic context, transitional organisms can be seen as representing early examples of a branch, where not all of the traits typical of the previously known descendants on that branch have yet evolved.{{sfn|Prothero|2007|p=[https://archive.org/details/evolutionwhatfos00prot_0/page/127 <!-- quote=fossil "transitional form". --> 127]}} Such early representatives of a group are usually termed "[[Basal (phylogenetics)|basal taxa]]" or "[[Sister group|sister taxa]],"{{sfn|Prothero|2007|p=[https://archive.org/details/evolutionwhatfos00prot_0/page/263 <!-- quote=fossil "transitional form". --> 263]}} depending on whether the fossil organism belongs to the daughter clade or not.<ref name="Palaeos" />