Evolution and Functional Anatomy of the Pectoral Fin Rays in Cyprinoid Fishes, with Emphasis on the Suckers (Family Catostomidae)

Abstract

The cyprinoid family Catostomidae exhibits 2 major trends in the evolution of pectoral fin rays: simplification of anterior rays and foreshortening of fin-ray segments. These structural modifications have developed along with behaviors that involve frequent contacts between the fins and the substrate, and have the effects of increasing flexibility, tensile strength and resistance to buckling of the fin rays. The degree of segment foreshortening is a good predictor of the general habitat ecology of catostomids. Elsewhere within the Cyprinoidei, pectoral-fin ray anatomy correlates well with behavior and ecology. Parallelism is the overriding pattern in the evolution of pectoral-fin ray structure in cyprinoids. Structural differences in fin-ray anatomy of the hill-stream fishes (homalopterids and gastromyzonids) suggest that their specializations to life in mountain streams were evolved independently. Similar trends in the evolution of fin rays are noted in the flatfishes (Pleuronectiformes), reedfishes (Polypteriformes), extinct rhipidistian crossopterygians and the living coelacanth, Latimeria chalumnae.