FQSSIL VERTEBRATES FISHES 4°5 



of the group. One thing is important, however, and that is the 

 changes that took place in the teeth of the many forms that 

 were developed during the Carboniferous time. There seems to 

 have been developed two types of teeth that indicate a very 



different mode of life. In one of these groups the teeth became 

 flattened and adapted to crushing or grinding the shells of 

 molluscs and crustaceans that formed the food supply. 1 he 

 faces of the teeth were sculptured in the most intricate manner, 

 affording an enlarged and more efficient triturating surface. 

 The different patterns of this sculpture seem almost endless. 

 'Jo these forms have been given the name of the "pavement- 

 toothed fanassa, Petalodm and Cockliodius, all from 

 the Carboniferous rocks are perhaps the best rep i oi 



group. CeUracion, the modern Port Ja< o shark, is the 



.e living representative. In the second group the teeth 

 eloped in acce with the demands of a more 



, •'; and rap< abii They are more or less triangular in 



outline, and l are frequently finely serrated, affording 



ry firm hol< a it cutting 01 gac 



This type reached its < tient later than the pavement- 



orn form, Corcharias/m ch th< 



reached a length of .six inc. - known from the Eocene of 



both the Old and the New Worlds. Other typical forms are 

 Sphenodus, Lamna, and Carcharodon from the Mesozoic of Europe 

 and many forms that are re >g< I a Carchariat in 



North America 



One - .il that must be mentioned is the Ichthyodcru 



lite. These are detach'- tt< greaf ab ' 



ance in the Carboniferous and Mesozoic rocks, and from which 

 a large number of genera have been named. Jn the mo< 



■ . the anterior end of the fins, and especiall the < oi al fin, 

 is frequently stn by the -. trong 



spine that serves as a cutwater. Thee spines werem 



ore primiti • e sharks and 

 to the greatest flcation in for::. and 



ornamentation. As they were >o strong they . c Id naturally 



