Editing Clade (section)

== Terminology ==
[[File:Primate cladogram.svg|thumb|left|Cladogram of modern primate groups; all tarsiers are haplorhines, but not all haplorhines are tarsiers; all apes are catarrhines, but not all catarrhines are apes; etc.]]
The relationship between clades can be described in several ways:
* A clade located within a clade is said to be ''nested'' within that clade. In the diagram, the [[Ape|hominoid]] clade, i.e. the apes and humans, is nested within the primate clade.
* Two clades are ''[[Sister group|sisters]]'' if they have an immediate common ancestor. In the diagram, lemurs and lorises are sister clades, while humans and tarsiers are not.
* A clade ''A'' is ''[[Basal (phylogenetics)|basal]]'' to a clade ''B'' if ''A'' branches off the lineage leading to ''B'' before the first branch leading only to members of ''B''. In the adjacent diagram, the [[Strepsirrhini|strepsirrhine]]/[[prosimian]] clade, is basal to the [[Hominoidea|hominoids]]/[[ape]] clade. In this example, both Haplorrhine as prosimians should be considered as most basal groupings. It is better to say that the prosimians are the sister group to the rest of the primates.<ref name="Krell-2004">{{cite journal |last1=Krell |first1=F.-T. |last2=Cranston |first2=P. |year=2004 |title=Which side of the tree is more basal? |journal=Systematic Entomology |volume=29 |issue=3 |pages=279–281 |doi=10.1111/j.0307-6970.2004.00262.x |s2cid=82371239 |name-list-style=amp |doi-access=free |bibcode=2004SysEn..29..279K }}</ref> This way one also avoids unintended and misconceived connotations about evolutionary advancement, complexity, diversity and ancestor status, e.g. due to impact of sampling diversity and extinction.{{citation needed|reason=reads as editorial comment|date=March 2019}}<ref name="Krell-2004" /><ref>{{Cite web|url=http://for-the-love-of-trees.blogspot.com/2016/09/the-ancestors-are-not-among-us.html|title=For the love of trees: The ancestors are not among us|last=Smith|first=Stacey|date=2016-09-19|website=For the love of trees|access-date=2019-03-23}}</ref> Basal clades should not be confused with stem groupings, as the latter is associated with paraphyletic or unresolved groupings.

=== Age ===
The age of a clade can be described based on two different reference points, [[crown group|crown]] age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its [[sister group|sister]] clade. A clade's stem age is either the same as or older than its crown age.{{sfn|Harmon|2021}} Ages of clades cannot be directly observed. They are inferred, either from [[stratigraphy]] of [[fossil]]s, or from [[molecular clock]] estimates.<ref>Brower, A. V. Z., Schuh, R. T. 2021. Biological Systematics:  Principles and Applications (3rd edn.). Cornell University Press, Ithaca, NY.</ref>