Cladistic Classification as Applied to Vertebrates

Abstract

It is the object of this paper to point out some consequences and problems arising from the use of cladistic classifications. However, we must initially clarify what is implied in the terms ‘phylogenetic systematics’ and ‘cladistics’. Phylogenetic systematics (exemplified by Hennig, 1966) encompasses the whole theory of classification in accordance with phylogeny (biological evolutionary history), while cladistics (which alludes to Rensch’s kladogenesis (1947, 1959) and to Huxley’s term clade (e.g. 1959) for a strictly monophyletic group) could perhaps with some advantage be restricted to the practical methodological approach, as developed by Hennig (e.g. 1966), Brundin (e.g. 1968), Nelson (e.g. 1971), Miles (1973), Patterson (1973) Rosen (1973), and others. Cladistics, however, has been used as a designation for the theory of phylogenetic systematics (e.g. by Mayr, 1974); although more often the word cladism has been so used (e.g. Mayr, 1969; Darlington, 1970; Nelson, 1971). Instead of having two more or less synonymous concepts it might be worthwhile restricting them to one as suggested above. The merit of this action is to recognize that workers other than the ones employing cladistic methods are con-vinced that they produce phylogenetic classifications (e.g. Simpson, 1959: 300). Thus phylogenetic systematics appears to be a goal that many post-Darwinian taxonomists have striven for (Nelson, 1971: 376; 1973: 372), while cladistics is a practical approach to that end. The practitioners of such an approach may well be termed cladists.