active taxon

Status of a taxon that has a complete phylogenetic definition and is actively employed by the compiler

active definition

Current compiler-accepted phylogenetic definition for a taxon


Monophyletic group


Person creating or authorizing taxon records for a TaxonSearch compilation; an original compiler is the first person to create a compilation; a secondary compiler is a person who gains access to a compilation, and modifies, a compilation originally created by someone else

crown clade

Clade defined by extant specifiers and whose immediate outgroup is extinct


Time horizon used as a qualifier in a phylogenetic definition

definitional author

Author of a phylogenetic definition

definitional component

A functional unit of a phylogenetic definition, which includes paradigms, specifiers, and qualifiers

definitional revision

Alteration of one or more components of a previous definition that results in either first- or second-order revision

definitional type

The fundamental kind of definition (node-based, stem-based), which are distinguished by the polarity of inclusion (least, most inclusive) and distinctive symbolic notation [T = (< A and BQ); T = (> AQ but not C)]

Symbols: T = taxon; ( ) = phylogenetic definition; <, > = polarity of inclusion; A-C = specifiers; Q = qualifier

earliest record

Earliest age (Ma = million years ago) assigned to any included species

first-order revision

Definitional revision that does not alter the definitional type or intended clade

inactive taxon

Status of a taxon that has no phylogenetic definition or is not currently in use by the compiler

latest record

Latest age (Ma) assigned to any includes species, or “Recent” (= 0) if there are extant members

mixed clade

Clade with living and extinct members that can only be defined by using at least one extinct specifier (because of basal extinct members)


A group composed if a real or hypothetical common ancestor and all of its descendants


Statement specifying the membership of a taxon as the least inclusive clade that contains at least two internal specifiers

node-stem triplet

Trio of taxa with complementary definitions consisting of a node-based taxon and two subordinate stem-based taxa

nominal author

Author who first coined a taxon name

2° nominal author

Author who coined a new taxon name within a family group that was already named by an earlier author


Fundamental manner in which a phylogenetic definition circumscribes a taxon; expressed in terms of the polarity of inclusion

phylogenetic definition

Statement specifying the membership of a taxon

potential synonomy

Comparable taxa that may be regarded as either junior or senior synonyms by some taxonomists

publication year (field in Active Phylogenetic Definition)

Year that a phylogenetic definition for an active taxon was first published which has the same definitional type and which identifies the same clade; year that the fundamental definitional concept was first published


Species or an attribute of a species or specimen cited in a phylogenetic definition as a dependent clause that qualifies clade membership


Duration of a taxon in millions of years (My) between the Earliest and Latest Records.  “Recent” is the Latest Record for a taxon with extant members

second-order revision

Definitional revision that intentionally identifies a different clade by using a different definitional type (node- vs stem-based) and/or by using alternative specifiers or qualifiers to intentionally identify a different clade


Shortened version of a phylogenetic definition that retains specifiers but eliminates authors, shortens qualifiers, and substitutes symbols for functions (e.g., < = “the least inclusive clade containing”)


Delimitation of clade membership by a phylogenetic definition


Species cited in a phylogenetic definition as an independent phylogenetic reference point

specifier A

Mandatory internal specifier

specifier(s) B

Optional internal specifier(s)

specifier(s) C

Optional external specifier(s)


Statement specifying the membership of a taxon as the most inclusive clade that contains at least one internal specifier

stem clade

Clade composed solely of extinct members whose immediate outgroup contains at least one living member

Symbolic notation

symbolic representation of a phylogenetic definition (e.g., T= (< A and BQ); general symbolic notation for a stem-based definition)

Symbols: T = taxon; ( ) = phylogenetic definition; < = “The least inclusive clade containing”; A = mandatory internal specifier; C = optional external specifier(s); Q = qualifier


Named clade (= monophyletic group)

taxon qualifier

Qualifier in a phylogenetic definition composed of species cited for inclusion (positive or “+ taxon”) or exclusion (negative or “- taxon”); can be used to limit the potential taxonomic content of a taxon

taxonomic content

Existing or potentially existing taxa or specimens that by definition are included within a taxon

textual substitution

Comparable phraseology between phylogenetic definitions that does not involve changes in a definitional component (paradigm, specifier, qualifier) and, as a result, does not constitute definitional revision