NUMERICAL EXPERIMENTS WITH MODEL MONOPHYLETIC AND PARAPHYLETIC TAXA

The problem of how accurately paraphyletic taxa versus monophyletic (i .e., holophyletic) groups (clades) capture underlying species patterns of diversity and extinction is explored with Monte Carlo simulations. Phylogenies are modeled as stochastic trees. Paraphyletic taxa are de fined in an arbitrary manner by randomly choosing progenitors and clus tering all descendants not belonging to other taxa. These taxa are the n examined to determine which are clades, arid the remaining paraphyle tic groups are dissected to discover monophyletic subgroups. Compariso ns of diversity patterns and extinction rates between modeled taxa and lineages indicate that paraphyletic groups can adequately capture lin eage information under a variety of conditions of diversification and mass extinction. This suggests that these groups constitute more than mere ''taxonomic noise'' in this context. But, strictly monophyletic g roups perform somewhat better, especially with regard to mass extincti ons. However, when low levels of paleontologic sampling are simulated, the veracity of clades deteriorates, especially with respect to diver sity, and modeled paraphyletic taxa often capture more information abo ut underlying lineages. Thus, for studies of diversity and taxic evolu tion in the fossil record, traditional paleontologic genera and famili es need not be rejected in favor of cladistically-defined taxa.