ATMOSPHERIC OXYGEN, GIANT PALEOZOIC INSECTS AND THE EVOLUTION OF AERIAL LOCOMOTOR PERFORMANCE

Uniformitarian approaches to the evolution of terrestrial locomotor ph ysiology and animal flight performance have generally presupposed the constancy of atmospheric composition. Recent geophysical data as well as theoretical models suggest that, to the contrary, both oxygen and c arbon dioxide concentrations have changed dramatically during defining periods of metazoan evolution. Hyperoxia in the late Paleozoic atmosp here may have physiologically enhanced the initial evolution of tetrap od locomotor energetics; a concurrently hyperdense atmosphere would ha ve augmented aerodynamic force production in early flying insects, Mul tiple historical origins of vertebrate flight also correlate temporall y with geological periods of increased oxygen concentration and atmosp heric density. Arthropod as well as amphibian gigantism appear to have been facilitated by a hyperoxic Carboniferous atmosphere and were sub sequently eliminated by a late Permian transition to hypoxia, For exta nt organisms, the transient, chronic and ontogenetic effects of exposu re to hyperoxic gas mixtures are poorly understood relative to contemp orary understanding of the physiology of oxygen deprivation. Experimen tally, the biomechanical and physiological effects of hyperoxia on ani mal flight performance can be decoupled through the use of gas mixture s that vary in density and oxygen concentration. Such manipulations pe rmit both paleophysiological simulation of ancestral locomotor perform ance and an analysis of maximal flight capacity in extant forms.