392 DE. G. ELLIOT SMITH ON 



division into orders and retain the term Edentata as a convenient if unnatural 

 expression. 



The labours of palaeontologists have been amply rewarded within recent years, 

 especially in North America, by excejitionally rich finds of extinct mammalian forms 

 which enable us to trace the genealogy of many of the great groups which have 

 survived until the present clay. In the light of the knowledge gahied from these records, 

 we can trace the ancestry of the carnivorous clawed mammals (Unguicuiata) and of the 

 herbivorous hoofed mammals (Ungulata) back to generalized forerunners, which at 

 the beginning of the Eocene period are with difficulty distinguishable the one from the 

 other. 



Not only is this so, but many of the contemporaries of these generalized forms which 

 inhabited the earth at the beginning of the Tertiary epoch are equally difficult to dis- 

 tinguish from these ancestors of the Carnivores and Ungulates. At this time we find a 

 huge multitude of primitive mammals — Creodonta, Condylarthra, Amblyopoda, Gano- 

 donta, Tillodontia, among others, — and so generalized are all these forms, that it is not an 

 easy matter to decide in the case of any whether we are dealing with the ancestor of 

 the Primate, the Carnivore, the Ungulate, the Edentate, the Rodent, the Insectivore, 

 or even the Marsupial. 



One of the most noteworthy features which all these generalized and primitive 

 mammals possess in common is the exceedingly small size of the brain. Eor at this 

 epoch the pallium had just made its first appearance, and the cerebellum was yet in a very 

 primitive condition. When we compare the diversely specialized forms which are rapidly 

 evolved fiom this simple generalized type as the brain increases in size, we are able to 

 appreciate how immense an impetus the forces of evolution received when a pallium 

 first made its appearance in the brain of the Saurian ancestor of the Mammalia. 



The profound effects of this important event almost immediately begin to manifest 

 themselves in the body generally, and become recorded for all time in the modifications 

 of the limbs which fossil forms present. Eor as complex muscular acts were rendered 

 possible by the development of the pallium, the skeleton became modified in adaptation 

 to these acts. The skeleton thus began " to assume characters and potentialities such 

 as it had not exhibited before, and an entu-ely new set of modifications " became 

 possible *. 



Under the potent influence of these new factors, which are so favourable to a rapid 

 adaptation to any circumstances in which the individual may happen to be placed, the 

 early mammal soon became specialized to various modes of fife, and developed new 

 forms of modifications with aU the exuberance of its newly-discovered potentiality to 

 excel. The effects of these modifications are most clearly demonstrated in the limbs 

 and in the teeth, and, most important of all, in the brain. 



In the keen struggle for existence, the mammal best equipped with a highly-developed 

 brain, which endows its possessor with the cunning and nimbleness which are of more 

 value than all the protective modifications, whether offensive or purely defensive, must 

 prevail. In the increasing competition among mammals, the], progressive perfection 



* A. S. Woodward, ' Yerlobrate Pala-ontology,' p. 246. 



