Aspects of the Physiology of Terrestrial Life in Amphibious Fishes

Bony fishes which could spend periods of time out of water, but which lacked special anatomical modifications for survival out of water, were probably involved in the early stages of the evolution of terrestrial life in the vertebrates. The rhipidistian crossopterygians were apparently the group ancestral to all higher vertebrates (Romer, 1966; Schmalhausen, 1968), but they are unavailable for study of possible physiological adaptations to life on the land. One way we may obtain some idea of the possible range of physiological adaptations which might have been possessed by these ancestral forms is to make comparative studies of pertinent aspects of the physiology of living amphibious fishes. We define amphibious fishes as those which spend periods of time out of water, on or above the ground surface, as normal parts of their life-histories. The most relevant forms are those lacking specialized accessory respiratory organs.