A taxonomic phylum is a major taxonomic rank conventionally below a taxonomic kingdom and above a taxonomic class. A particular phylum is a taxon at that rank. For example, chordates form the phylum containing Mammalia, which in turn contains orders such as Carnivora.[ref]
The same animal can consequently belong to a phylum, a class and an order without these being competing identifications. Each level adds information about nested membership. The rank word phylum identifies a position in the hierarchy; the group name identifies which taxon occupies that position.
For a constructed survey example, suppose one phylum is represented by four sampled classes with 3, 7, 2 and 8 sampled species. Its total is . A second phylum with two sampled classes containing ten species each has the same total. Reporting only twenty species for each phylum loses the class-level distribution, and neither count establishes the total diversity of the unsampled phylum.
A taxonomic rank does not itself specify a fixed age, number of constituent groups or numerical genetic distance. A phylogenetic tree addresses evolutionary relationships, while ranked names select particular groupings for classification.[ref] The usefulness of the rank comes from organizing comparisons; the scientific interpretation still depends on what was sampled and the evidence supporting membership.
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