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Draft guidelines
An article about a species is categorized by the year in which the species was formally described according to the relevant nomenclature code (e.g. the International Code of Zoological Nomenclature or the International Code of Nomenclature for algae, fungi, and plants). The top level category is Category:Species by year of formal description.
Only species articles are categorized by formal year of description, because the top level category is Category:Species by year of formal description. A species article should be placed in a category with the title "Xs described in YEAR", e.g. Category:Plants described in 1812, Category:Fungi described in 1950, or Category:Spiders described in 1850. The kind of organism should be selected to be as specific as possible within the range of existing categories, e.g. Category:Spiders described in 1850 rather than Category:Animals described in 1850.
The "Xs described in YEAR" categories are placed in container categories, such as "Xs described in CENTURY" categories. These categories are always container categories, so articles should only ever be placed in an "Xs described in YEAR" category.
It can be useful to subdivide large groups of organisms, such as "Animals described in YEAR" into more specific categories, such as "Birds described in YEAR", e.g. Category:Birds described in 1794. Such subdivisions should only be created
- where there is a corresponding wikiproject that will take ownership and consensus has been reached at the wikiproject to create the categories and for the wikiproject's template to be placed on the categories' talk pages
- when there is a commitment to set up a more-or-less complete set of "Xs described in YEAR" categories, rather than a few random years.
The diagram below shows an example of how the category hierarchies are set up when there is only one taxonomic level below "species", in this case "plants", and when DECADE categories are present.
For other kinds of organism, there may be additional "columns". The diagram below shows how the category hierarchy was set up for birds, as of April 2018[update].
Navigation templates
editFor "Xs described in YEAR" categories, both navigation backwards and forwards by year and appropriate parent categories can be set up using the template {{Category described in year}}. No parameters are needed; the page name is used to obtain all the required information. For example, at Category:Fish described in 1974, using {{Category in year}} adds a navigation bar and automatically places the category in Category:Fish described in the 20th century and Category:Animals described in 1974.