A functional analysis of the aquatic and aerial respiratory movements of an African lungfish, Protopterus aethiopicus, with reference to the evolution of the lung-ventilation mechanism in vertebrates.

Abstract

ABSTRACT Recent palaeontological evidence (Jarvik, 1967; White, 1966) indicates that the Dipnoi should be regarded as a specialized group of fishes, which have been structurally different from the Rhipidistia (now thought to have included the prototetrapods) for as long as the fossil record can yet show. However, the homology of the dipnoan lung with that of the tetrapod, and the similarities of organization and development between living Dipnoi and Amphibia, might indicate a closer relationship between the two groups than can be revealed by palaeontological studies. The level of organization seen in the living Dipnoi is not thought to be basically different from that of the Devonian forms and a study of the physiology of these animals must expand our knowledge of the development of vertebrate physiological mechanisms. Since the Dipnoi are adapted to a habitat very similar to that in which the first terrestrial verte-brates are thought to have evolved, and since they possess functional aerial and aquatic respiratory systems, a study of respiratory function in these animals may help to elucidate the manner in which the ancestral tetrapods became able to colonize the terrestrial habitat.