20.1
Citation of nominal and definitional authors (Art. 19.1) is optional, but if authors are cited, Articles 20.2–20.8 are to be followed.
20.2
Authors’ names are to be cited after the clade name. Nominal authors of any name, whether preexisting or new, are to be cited without enclosing symbols. Definitional authors, if different from the nominal author(s) of the name in question (Note 19.1.2 and Note 20.2.1), are to be cited within enclosing symbols: the authors of the original definition (i.e., the definitional authors of a converted name) are to be cited in square brackets ([ ]; Art. 20.4, Ex. 1); the authors of an emended definition are to be cited in braces ({ }; Art. 20.6, Ex. 1).
Note 20.2.1
If the nominal and definitional authors are the same (as for most new clade names; see Note 19.1.2), they are to be cited as nominal authors, and thus no enclosing symbols are to be used.
20.3
If more than one set of authors is cited, they are to be cited in the following order: nominal author(s) of the preexisting or new name (including a replacement name); author(s) of the original definition; author(s) of an emended definition.
20.4
If the definitional authors of a converted name are cited, the nominal authors of the preexisting name on which it is based, if known, must also be cited.
Example 1
Suppose that Larson established a converted clade name Hypotheticus in 2020 based on the preexisting name Hypotheticus of Meekins (published in 1956). In this situation, the citation of the converted name would be Hypotheticus Meekins [Larson]. Meekins is the nominal author; Larson is the definitional author.
Example 2
If Larson established a converted clade name Hypotheticus based on the preexisting name Hypotheticus, and if the authorship of this name were unknown, the citation of the converted name would be Hypotheticus [Larson].
Note 20.4.1
The publication years of the preexisting name and converted name may follow the names of the respective authors.
Example 1
Using Example 1 of Article 20.4, the citation with publication years would be Hypotheticus Meekins 1956 [Larson 2020].
Recommendation 20.4A
If a preexisting name was used in association with more than one rank or composition, and authorship is cited, the nominal author(s) cited should be the original author(s) of the name, as spelled for the purpose of conversion, rather than the first author(s) who applied the name later in association with a different rank or composition (but see Rec. 9.15A).
Recommendation 20.4B
If a preexisting name has been attributed to an author or authors other than the first author(s) who used the name being converted (as can occur under the Principle of Coordination of the ICZN), the nominal author(s) cited should not be the former but rather the author(s) of the name as spelled for the purpose of conversion (but see Note 9.15A.3 and its Ex. 1).
20.5
If the nominal authors of a replacement name are cited, the definitional authors of the replacement name (i.e., the definitional authors of the replaced name; see Arts. 13.5, 19.3) must also be cited.
Example 1
Suppose that Holmes was the definitional author of the name Cladus, which turned out to be a later homonym of Cladus (established by a different author), and then Clarke published the new name Imaginarius as a replacement name for Cladus Holmes. The full citation of the replacement name would be Imaginarius Clarke [Holmes]. If, instead, Clarke had converted the replacement name from the preexisting name Fabricatus Merriam, the full citation of the replacement name would be Fabricatus Merriam [Holmes].
20.6
If the authors of an emended definition (see Art. 15) are cited, the authors of the original definition must also be cited.
Example 1
If Fictitius was established as a new name by Stein, and Maki subsequently emended Stein’s definition, the full citation would be Fictitius Stein {Maki}. If, instead, Stein had converted Fictitius from the preexisting name Fictitius Merriam, the full citation would be Fictitius Merriam [Stein] {Maki}.
20.7
When authorship of a name differs from authorship of the publication in which it is established, both may be cited, connected by the word “in.” In such a case, “in” and what follows are part of a bibliographic citation and are only to be included if the publication is referred to, at least by its year.
20.8
The optional use of “ex” under the ICNAFP to cite author(s) to whom the name, but not the rest of the protologue, is attributable is not adopted in this code.
Recommendation 20A
Bibliographic references to the protologue of established names are available in the registration database and may be accessed by either clade name or registration number. However, only the registration number is reliably unique. Therefore, in cases of potential ambiguity, the registration number should be cited at least once in any publication in which the corresponding name is used.