THE LINEAGE OF MAN 



known lines were then near the end of their career; second, 

 the shark group, at that time relatively small, which was to 

 become highly diversified in the next period and then to be 

 crowded almost to the wall by the higher fishes; third, the 

 true ganoids (actinopts), ancestors of the sturgeons, spoon- 

 bills, bony gars, and eventually of the higher or teleost fishes; 

 fourth, the dipnoans or lung-fishes, and fifth, the lobe-finned 

 or crossopterygian ganoids, to be described presently. 



Among which, if any, of these groups are we to seek for 

 the ancestors of the higher vertebrates, including man? The 

 known ostracoderms of Devonian time were already special- 

 ized side branches, all far too late in time to be the actual 

 ancestors of the higher vertebrates. The Devonian sharks 

 were already giving rise either to the specialized side 

 branches or to the ancestors of the modern sharks ; the acti- 

 nopt ganoids were already on the line of advance to the 

 higher fishes; the dipnoans were already highly specialized 

 in their dental apparatus and skull characters and well along 

 on the line to their modern descendants. Only certain of the 

 lobe-finned fishes seem to have the right combination of 

 characters to be even nearly related to the direct ancestors 

 of the land-living vertebrates. 



What, then, are the broad characteristics of these interest- 

 ing fossil fishes, some of which may lie relatively near to 

 the line of our own ancestry? Some of them were long- 

 bodied, pike-like fishes, with great, strong jaws armed with 

 sharp teeth. Others were stout and heavy-bodied, somewhat 

 like a sea-bass, with shorter jaws. One very specialized 

 group that lasted for many millions of years was short- 

 bodied, propelled by fan-shaped paddles and by a very broad 

 tail. Of all these, only the first lot, including Osteolepis, 

 Megalichthys, Eusthenopteron and their allies, appear to be 

 near the line of ascent to the land-living vertebrates. In 



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