SYNOPSIS. Notions of functional and behavioral transformations among traits of similar organisms are ad hoc unless viewed within the context of a corroborated scheme of relationships of the taxa involved. For purposes of exposition a current best estimate of the interrelationships of the main groups of teleosts (as expressed by a branching diagram or cladogram) is used as a basis for evaluating the transformations of feeding and locomotor mechanisms. When the various states of these mechanisms are incorporated into the branching structure, the cladogram, when interpreted historically, specifies certain conceptual constraints such that, 1) specializations of the upper jaw first arose and proliferated before specializations of the paired fins, and 2) that fin spines arose only after changes in both feeding and locomotor mechanisms were well under way. These results are contrasted with familiar though unsupported adaptationist statements about the relative importance of locomotor and feeding mechanisms for the evolution of the spiny-finned teleosts (acanthopterygians)—a contrast between the interpretation of what happened as opposed to why it happened. The particular reasons why a given structure, function or behavior exists are unknowable and theories addressing such questions are untestable. Adaptationist arguments in general are framed in terms of forces external to the organism which impose a process of change that leads to good design. The concept of an external agency or process (such as selection) that can design structures or whole organisms to fit their environments, even when stated in rigorously biological language, are effectively the same, and almost as far removed from the empirical data, as the creationist argument for adaptation. To the extent that the empirical data of systematics are not allowed to constrain the evolutionary interpretation of functional anatomists, their explanation of historical change will be limited only by their own inventiveness and the gullibility of their audience.