Phylogenetic definitions in the pre-PhyloCode era; implications for naming clades under the PhyloCode

3rd May 2007

Michael P. Taylor
Palaeobiology Research Group, School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth PO1 3QL, UK

The last twenty years of work on phylogenetic nomenclature have given rise to many names and definitions that are now considered suboptimal. In formulating permanent definitions under the PhyloCode when it is implemented, it will be necessary to evaluate the corpus of existing names and make judgements about which to establish and which to discard. This is not straightforward, because early definitions are often inexplicit and ambiguous, generally do not meet the requirements of the PhyloCode, and in some cases may not be easily recognizable as phylogenetic definitions at all. Recognition of synonyms is also complicated by the use of different kinds of specifiers (species, specimens, clades, genera, suprageneric rank-based names, and vernacular names) and by definitions whose content changes under different phylogenetic hypotheses. In light of these difficulties, five principles are suggested to guide the interpretation of pre-PhyloCode clade-names and to inform the process of naming clades under the PhyloCode: (1) do not recognize "accidental" definitions; (2) malformed definitions should be interpreted according to the intention of the author when and where this is obvious; (3) apomorphy-based and other definitions must be recognized as well as node-based and stem-based definitions; (4) definitions using any kind of specifier taxon should be recognized; and (5) priority of synonyms and homonyms should guide but not prescribe. Strict priority should not be observed in the pre-PhyloCode era, and should not determine which existing names are permanently established; precedence should begin only with the formal establishment of the PhyloCode.


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