ARE PHYLOGENETIC NOMENCLATURE AND INVERTEBRATE PALEONTOLOGY FRIENDS OR FOES?

Phylogenetic nomenclature is an approach to naming taxa that makes explicit reference to a hypothesis of common ancestry. The approach has engendered strong, often emotional, responses, both positive (e.g., Brochu and Sumrall, 2001) and negative (e.g., Benton, 2007). Apart from arguments concerning explicitness and stability, and the pros and cons of ranks, my experience with the process of constructing phylogenetic definitions for the PhyloCode Companion Volume has convinced me that this is a thoughtful, informative, and valuable approach, especially for paleontologists. When investigating morphological character evolution, as well as the definition and internestedness of Linnean taxa in a group like the brachiopods with a long, diverse fossil record and few extant taxa, our focus is more productively directed to testing hypotheses of homology and polarity than simply assigning specimens to named taxa based on the possession of key features. Crown clade, total clade, and stem group concepts help to better organize and evaluate data that bear on long-standing issues of taxon names and boundaries, and character origin and evolution. Are phoronids brachiopods? How does a bivalved shell evolve? How are brachiopods related to other lophotrochozoans, what fossils are stem-group brachiopods, and what is the evolutionary history of the lophophore? The crown clade of articulated brachiopods is now defined, for the first time, and, in the process, evolution of valve articulation, shell endopunctation, and calcareous lophophore supports are reevaluated. The significance of a calcitic shell, with a fibrous or laminar microstructure is clarified.

From the perspective of phylogenetic nomenclature, named taxa signify more than counts in diversity estimates. The approach does not require the abandonment of ranks; rather, I argue that it enhances our understanding of ranks, and taxa named at different ranks, from an evolutionary perspective. To focus effectively on macroevolutionary issues, Linnean taxonomy alone is insufficient. Adopting the approach of phylogenetic nomenclature, in concert with Linnean taxonomy, we will be better able to evaluate the effects of extinction and diversification within clades as crown, stem and total groups are more clearly delineated and defined.