THE PALEONTOLOGIC RECORD 



35 



is more than divergence because it implies evolution in every direction 

 from a central form. The idea of radii, or radiations from a central 

 form greatly assists the imagination, because a distinctive feature of 

 paleontology is that we are constantly dealing with fragments of his- 

 tory. The radiations which have been discovered must be supple- 

 mented by those which remain to be discovered, and it is very remark- 

 able how in group after group of animals these missing " radii " have 

 turned up. 



Eadiation actually begins in certain single organs, and the first 

 principle to be observed, as shown in the accompanying diagram, is 



LIMBS AND FEET 



VOLANT 



FOSSORIAL 



ARBOREAL 



Short-limbed, plantigrade, 1 AMBULATORY 

 pentadactyl, unguicu- I OB 



late Stem J TERRESTRIAL 



NATATORIAL 

 Amphibious 



CURSORIAL 

 Digit igrade 



Aquatic 



Unguligrade 



TEETH 



OMNIVOROUS 



(Fish 

 Flesh 

 Carrion 



HERBIVOROUS ^ 



Grass 



Herb 



Shrub 



Fruit 



Root 



MYRMECOPHAGOUS 

 Dentition reduced 



Stem INSECTIVOROUS 

 MAIN LIKES OF ADAPTIVE RADIATION OF (a) limbs and feet, (6) teeth among mammals. 



