THE ORIGIN AND EVOLUTION OF LIFE ON THE EARTH
By Henry Fairfield Osborn
COLUMBIA UNIVERSITY, AMERICAN MUSEUM OF NATURAL HISTORY
LECTURE II PART II
EVOLUTION OF THE FISHES
FOLLOWING the pro-fishes of Odrovician time (p. 508) the great group of fishes begins its evolution with (A) active, free-swimming, double pointed types of fusiform shape, adapted to rapid motion through the water and to predaceous habits in pursuit of swift-moving prey. From this type there radiated many others: (B) the deep, narrow-bodied fishes of relatively slow movements, frequenting the middle
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Fig. 9a. Origin and Adaptive Radiation of the Fishes showing the Now Extinct Silubo-Devonian Groups, the Ostracoderms and Arthrodires, in relation to the surviving lampreys (Cyclostomes), sharks, and rays (Elasmobranchs), sturgeons, garpikes, bowfins (Ganoids), bony fishes (Teleosts), primitive and recent lung-fishes (Dipnoi), and finally the fringe-finned Ganoids (Crossopterygil) from the cartilaginous fins of which the fore and hind limbs of the first land-living vertebrates (Tetrapoda) were derived. Dotted areas represent groups which still exist. Hatched areas represent extinct groups. Prepared for the author by Wm. K. Gregory.
depths of the waters; (D) the swift-moving, elongate types which increasingly depended upon lateral motions of the body for propulsion and thus tended to lose the lateral fins and finally to assume an elongate, eel shape entirely finless; (C) other bottom-living forms in which the body became laterally flattened, the head very large relatively and covered with protective dermal armature, the movements of the animals very slow.
