In zoological nomenclature, an unavailable name is a name that does not conform to the rules of the International Code of Zoological Nomenclature and that therefore is not available for use as a valid name for a taxon. Such a name does not fulfil the requirements in Articles 10 through 20 of the Code, or is excluded under Article 1.3.
Unavailable names include names that have not been published, such as "Oryzomys hypenemus" and "Ubirajara jubatus", names without an accompanying description (nomina nuda), such as the subgeneric name Micronectomys proposed for the Nicaraguan rice rat, names proposed with a rank below that of subspecies (infrasubspecific names), such as Sorex isodon princeps montanus for a form of the taiga shrew, and various other categories.
Despite the frequent confusion caused by common sense, an unavailable name is not necessarily a nomen nudum. A good examplification of this is the case of the unavailable dinosaur name "Ubirajara jubatus", which was assumed by common sense to be a nomen nudum before a detailed analysis of its nomenclatural status.
- Caetano, João Marcus Vale; Delcourt, Rafael & Ponciano, Luiza Corral Martins de Oliveira (March 2023). "A taxon with no name: 'Ubirajara jubatus' (Saurischia: Compsognathidae) is an unavailable name and has no nomenclatural relevance". Zootaxa. doi:10.11646/zootaxa.5254.3.10.
- Hershkovitz, 1970, pp. 789, 791
- Hutterer & Zaitsev, 2004, p. 89
- Hershkovitz, P. 1970. Supplementary notes on Neotropical Oryzomys dimidiatus and Oryzomys hammondi (Cricetinae). Journal of Mammalogy 51(4): 789-794.
- Hutterer, R. & Zaitsev, M.V. 2004. Cases of homonymy in some Palaearctic and Nearctic taxa of the genus Sorex L. (Mammalia: Soricidae). Mammal Study 29:89-91.
- International Commission for Zoological Nomenclature. 1999. International Code of Zoological Nomenclature, 4th edition. London: The International Trust for Zoological Nomenclature. Available online at https://web.archive.org/web/20090524144249/http://www.iczn.org/iczn/index.jsp. Accessed September 27, 2009.