Morphology and Interrelationships of Primitive Actinopterygian Fishes

SYNOPSIS. The concept of the Actinopterygii as a natural group of fishes was not generally accepted until early in this century. Ever since, the characterization of the group has been blurred by the problem of cladistian (polypterid) relationships. From a review of the structure of polypterids and actinopts, it is concluded that Cladistia are the sistergroup of Recent actinopterygians (Actinopteri), the two groups together comprising the Actinopterygii. Recent chondrosteans are more closely related to higher actinopts (Neopterygii) than to cladistians. The extinct Palaeonisciformes appear to be a paraphyletic group, comprising stem-group actinopterygians (e.g., Cheirolepts), stem-group actinopterans (e.g., Moythomasia) and relatives of higher actinopterans (e.g., Pteroniscus)