Change in fin morphology and position is a central component of the evolutionary transformation of functional design in ray-finned fishes (Actinopterygii). Documenting phylogenetic patterns in the structure of the paired and median fins, and interpreting the functional significance

component of the evolutionary transformation of functional design in ray-finned fishes (Actinopterygii). Documenting phylogenetic patterns in the structure of the paired and median fins, and interpreting the functional significance of such patterns, has been the subject of ongoing study by systematists, functional morphologists and hydrodynamicists (e.g. Breder, 1926; Harris, 1953; Aleev, 1969; Lighthill, 1969; Gosline, 1971; Alexander, 1974; Rosen, 1982; Lauder, 2000). Of the propulsors employed by fishes, one of the least well understood from a mechanistic perspective is the dorsal fin, which is characterized by an evolutionary trend of anatomical elaboration. The plesiomorphic condition exhibited by most basal teleost fishes is the possession of a single soft-rayed dorsal fin (e.g. Fig. 1: Clupeiformes, Salmoniformes). In contrast, more derived teleosts typically have two distinct dorsal fins, the first (anterior) stiffened by spines and the second (posterior) soft-rayed (Lauder and Liem, 1983; 2943 The Journal of Experimental Biology 204, 2943–2958 (2001) Printed in Great Britain © The Company of Biologists Limited 2001 JEB3613