208 



Increase in Number of Species 



focene \ 

 Pakocene 



P/eistocene 



Pl/ocene 



Mocene 



Oliqocene 





CO 

 < 



t- 



Art/cu/c7ta 



I \£urASiat^c f en. ^ specter \ .'A furajuiiLC ip^ci es of coJ/nepoltih^ 



\4m^'-u:aA. ipfc^j of co-fnafioU&^/t-fe^t^rt 



Am^rtca/t. ^ffx. Sfjpfc^^es 



Fig. 89. The numbers of the echinoderm class Crinoidea known from various 

 times, ilhistrating the drastic reduction of species which has occurred. Only a 

 few species exist today. (After R. C. Moore.) 



Sabrosky, 1952). Adding estimates of species yet unknown, the 

 actual total may be as high as 2 to 5 million. It seems reasonable to 

 suppose that the total number formed through all biologic evolu- 

 tion has been many times greater (Simpson, 1952; Teichert, 1956). 



