Cladistics and Stratigraphy

Abstract

Using cladistic phylogenies (cladograms) to evaluate stratigraphy (taxon distributions and correlations) necessitates various assumptions that include all of the assumptions built into the cladogram, assuming the cladogram is “correct” and that new taxa only arise by dichotomous splitting. Ghost lineages extend back the temporal ranges of sister taxa by assuming that both taxa’s oldest records are the time of dichotomous splitting, the only mode of evolution in cladistics. Other modes of evolution require no ghost lineages (anagenesis) or indicate unequal temporal ranges of closely related taxa (punctuation). Evaluating congruence between cladistic branching patterns and stratigraphic distributions reveals much congruence, simply because the cladogram and the taxa in the stratigraphic distribution are overlapping datasets, and the pattern of evolution is to evolve derived taxa after more primitive taxa. Correlating fossil assemblages based on the phylogenetic signals of their included taxa is little more than correlating by stage of evolution. Claiming that paraphyletic taxa are of less biochronological utility than monophyletic taxa is not borne out by examining correlations provided by the actual stratigraphic ranges of the taxa, regardless of their status in an a posteriori cladistic analysis. Thus, using cladistics to evaluate stratigraphy is assumption laden and of questionable value.