lyo 



THE ORIGIN AND EVOLUTION OF LIFE 



ered fishes {Osteolepis, Cheirolepis) now makes its first appear- 

 ance. These armored knights of the sea are descended from 

 simpler scaly forms which also gave rise to the rich stock of 

 sturgeons, garpikes, bowfins, and true bony fishes (teleosts) 

 which now dominate all other fish groups both in the fresh 



Fig. 51. Fish Types from the Old Red Sandstone of Scotland. 



Upper Devonian time. Primitive ganoids, primitive spine-finned sharks, bottom-living 

 Ostracoderms, partly armored ganoids, and the first lung-fishes, i. Osteolepis, primitive 

 lobe-finned ganoid. 2. Holoptychius, fringe-finned ganoid. 3, 6. Cheiracanthus, spine- 

 finned shark (Acanthodian). 4. Diplacanthus, spine-finned shark (Acanthodian). 

 5. Coccosteus, primitive Arthrodiran. 7. Cheirolepis, primitive ganoid. 8, 9. Dipterus, 

 primitive lung-fish. Pterichthys, bottom-living Ostracoderm allied to Bothriolepis. 

 Restorations by Dean, Hussakof, and Horter, partly after Traquair. Models in the 

 American Museum of Natural History. 



waters and the seas. Remotely allied to this stock are the 

 first air-breathing lung-fishes (Dipnoi), represented by Dipterus; 

 also the "lobe-finned," or "fringe-finned" ganoids from which 

 the first land vertebrates were derived. From a single locality, 

 in the Old Red Sandstone of Scotland, Traquair has recovered 



