EOCENE PERIOD 123 



creatures disappeared about the same time : but in late 

 Eocene times the Order was represented on that continent 

 by beasts, with still less brains, it is true, but of much more 

 imposing aspect (Dinocerata). Some of these animals were as 

 large as elephants, and were well armed (Dinoceras). Not 

 only were their upper canines developed into powerful tusks ; 

 but their heads were furnished with four horns, and a pair of 

 knobs adorned the snout. They had also improved on their 

 forerunners in locomotive powers, for they had become 

 distinctly digitigrade. One might suppose that such lordly 

 creatures would have held their own in the world for a long 

 time ; but such was not the case ; for at the close of the 

 Period they became quite extinct. There is little doubt that 

 intelligence was beginning to play a very important part in 

 animal progress ; and as regards brains these animals were 

 excessively deficient. Dinoceras is suggestive of a battle-ship 

 in charge of a child. 



Meanwhile the Order of Rodents (which comprises squirrels, RODENTS 

 hares, rats, and other animals with chisel-shaped incisor 

 teeth) was coming into view. As far back as Jurassic times 

 certain primitive mammals were developing teeth of a rodent 

 or gnawing type : but so far as is known neither those 

 animals, nor their Cretaceous successors, were much advanced 

 on the way to becoming true rodents. In early Eocene 

 times much more clearly defined rodent mammals were in 

 existence (Esthonyx). These on account of their " tearing " 

 teeth are known as Tillodonts, and they are generally re- 

 garded as the ancestors of living rodents. 



As regards teeth these ancestral forms were more liberally 

 supplied than are the living representatives of the Order. 

 Abundance of teeth, however, was a great feature with early 

 mammals. Dental modification, in course of time, resulted 

 in reducing the number, and increasing the efficiency of the 

 remainder for the various habits of life that were being 

 adopted. This reduction appears, geologically speaking, to 

 have been a rapid process in the case of the rodents ; for as 

 the Period advanced one pair of the upper incisors was 

 disappearing (Anchippodus). Provision was at the same 

 time being made for the continuous growth of the large 



