Evaluation of the Efficacy of Numerical Taxonomic Methods: An Example from the Bivalve Mollusks

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Abstract
Bretsky, Sara S. (Northwestern Univ., Evanston, III. 60201) 1971. Evaluation of the efficacy of numerical taxonomic methods: an example from the bivalve mollusks. Syst. Zool. 20:204–222.—Phenetic and phylogenetic classifications of 42 Tertiary and Recent species of the Family Lucinidae (Mollusca, Bivalvia) correspond reasonably well only at the lower taxonomic levels. On the basis of their evolutionary relationships, these species can be assigned to 28 subgenera and 7 genera. In the phenetic study, 45 multistate, mostly qualitative characters were used to calculate correlation and distance coefficients; both similarity measures were clustered by the weighted pair-group method. Small clusters which formed at high similarity levels in the two phenograms were usually composed of species of one subgenus or two or three closely related subgenera. Major clusters in each of the phenograms, however, differed considerably both from those of the other phenogram and from the principal phylogenetic lineages (genera). “Cophylogenetic coefficients,” analogous to the cophenetic coefficients used in comparing phenograms, indicated that both phenograms poorly reflected inferred phylogeny and that they did not differ significantly with regard to their correspondence to the phylogenetic classification. Simple cluster analysis probably is adequate for finding phylogenetic groups at the subgeneric level but not for recognition of higher taxa. At the generic and higher levels, phenetic classifications are not more stable than phylogenetic ones. Phylogenetic classifications, being hypotheses about genealogy rather than static descriptions of morphological similarity, are more likely than phenetic ones to be productive of future investigations.

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