Explicitness, Stability, and Universality in the Phylogenetic Definition and Usage of Taxon Names: A Case Study of the Phylogenetic Taxonomy of the Carnivora (Mammalia)

Abstract

In phylogenetic taxonomy, the clade denoted by a taxon name is determined by the phylogenetic definition of the name and by the phylogenetic context. The clade referred to by the phylogenetic definition of a taxon name depends on (1) the reference phylogeny, (2) the meanings of taxon names referred to in the definition, and (3) whether the name is defined as a node-, stem-, or apomorphy-based taxon. Ambiguity in the clade referred to by the definition results from (1) imprecise wording so that no single ancestor is specified, the clade identified by the definition changes with the extinction of taxa, or the definition is a tautology, (2) failure to specify a reference phylogeny, and (3) the lack of phylogenetic definitions of taxon names referred to in the definition. In phylogenetic taxonomy, phylogenetic pattern has the central role in determining the identity and attributes of the clades denoted by particular taxon names. Because phylogenetic definitions may associate taxon names with different clades on different cladograms, definitions may have to be emended with changes in our understanding of phylogeny to preserve the association be- tween a taxon name and a particular clade. As phylogenetic hypotheses stabilize, so will the definitions and usage of taxon names. Conventions can promote universality in the formation, definition, and usage of taxon names in phylogenetic taxonomy. Ambiguity is reduced by using standard formats for node- and stem-based definitions and by citing authorities for the meaning of taxon names used in definitions. Reference to undefined taxon names in definitions can be avoided by referring instead to the species referred to that taxon in a standard taxonomic reference. Rec- ommended usages of taxon names provide a mechanism for restricting the use of a name to a clade with a particular exclusive common ancestry. Continuity of usage should help to promote the ac- ceptance of phylogenetic taxonomy by biologists. These issues are discussed within the context of the phylogenetic taxonomy of the Carnivora. (Carnivora; nomenclatural stability; phylogenetic def- inition; phylogenetic taxonomy; taxon names; taxonomic conventions; taxonomic usage.)