Webb, G.E. 1994 1015: Parallelism, non-biotic data and phylogeny reconstruction in paleobiology.
Many systematists equate parallelism and convergence. However, whereas convergence is relatively uncommon and easily recognized using divergent characters, parallelism is common but more difficult to recognize because divergent characters are less abundant. Cladists, in particular, equate homeomorphy with convergence and reject parallelism as a distinct concept. Unfortunately, cladistic parsimony analysis may not resolve most parallelism. Therefore, criteria for the a priori recognition and objective evaluation of parallelism are very significant. Non-biotic data (e.g., stratigraphic and geographic distribution) provide independent criteria for the construction of hypotheses of parallelism in cases where taxa (1) were geographically isolated during homeomorphic character-state transformations, (2) occurred with endemic faunas, and (3) evolved in similar environmental conditions as suggested by paleoecological data. Australian lithostrotionoid corals were long considered congeneric with European taxa. However, because of their geographic isolation, occurrence with endemic rugose corals and occurrence in similar depositional environments as European forms, they are now considered a homeomorphic clade, resulting from an extended sequence of parallel character-state transformations. The high degree of parallelism, combined with abundant symplesiomorphic characters, led to erroneous phylogenetic inferences when non-biotic data were excluded from analysis. Cladistics, homeomorphy, lithostrotionoid corals, parallelism, phylogeny.