COMPARATIVE TAXONOMY: A METHOD TO TEST THE HYPOTHESES OF OPPONENTS OF TAXIC PALEOBIOLOGY

Taxic paleobiology uses supraspecific taxa (usually genera and families) to estimate diversification and extinction patterns. This methodology has been attacked on a number of bases, including: 1) most published supraspecific taxa are not monophyletic; their disappearance from the fossil record does not constitute extinction of a supraspecific taxon, 2) generic and familial taxonomy within a given higher taxon (i.e., order) differs between taxonomists; using taxonomic diversity data to study diversification and extinction patterns instead studies biases of subjective taxonomists, 3) higher taxonomic ranks are constructs, the only real taxon is the species, 4) the fossil record is incompletely known. For these and other reasons it has been argued that some reported episodes of diversification and extinction revealed by taxic paleobiological studies are artifacts. However, most of these arguments have been assertions lacking data to support their hypotheses. To test the hypothesis that taxic paleobiology studies the biases of taxonomists and that some episodes of diversification and extinction are products of said biases, we use the taxonomy of cockles (Cardiidae), one of the best-known and thoroughly studied clades of bivalves. There are several competing taxonomies of cockles, all of which use both genera and subgenera: Keen 1969 (Treatise), Keen 1980, Fischer-Piette, Popov, Sepkoski, and Schneider. The null hypothesis of taxic paleobiology's opponents - differing taxonomic systems are significantly different from each other - is tested and rejected for both genera and subgenera. Although amplitude varies between taxonomists (i.e., lumpers and splitters), the shape of the diversity curve does not differ from one author to the next; this even though Schneider has found that previous workers used not just paraphyletic but polyphyletic groups; Fischer-Piette even violated ICZN rules. The only phylogenetically-based taxonomy - Schneider - displays the sharpest peaks and valleys, suggesting that the problem with using non-phylogenetically based taxonomies is not that periods of origination and extinction are artifacts, but that use of higher taxa and non-monophyletic groups makes real episodes of increased diversification and extinction more difficult to discern.