COELACANTH FISHES — WHITE 



359 



AGE IN 

 MILLIONS 

 OF YEARS 



I'M 

 170 



1« 

 220 



320 

 350 



Figure 3. — Diagram showing the relationships of the coelacanths to other backboned 

 animals and their distribution in the geological succession. Time in millions of years. 

 (Courtesy of Discovery.) 



The third group of fringe-finned fishes were the coelacanths, and 

 their story is the least eventful of them all: it shows remarkably 

 little in the way of evolutionary change. The coelacanths had two 

 great disadvantages compared with their relations. They had no 

 through passage from their nostrils into their mouths — whether they 

 once had one but lost it early, or whether they never had such a 

 passage the records do not show — and, as we have already noted, their 

 lung or air sac was sheathed in bony scales. What purpose this 

 served, scientists would like to know. It must have had a function 

 of some importance, for it was a conspicuous feature in the fossils 

 for about 200 million years : it may have acted as a resonator, increas- 

 ing their perception of sound waves, as the air sac does in some modern 

 fishes. We do know, however, that the coelacanths neither went 

 up the scale of life nor down — they just remained coelacanths. They 



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