JURASSIC PERIOD 97 



of the wing, and its deficiency of strength owing to the non- 

 ] unction of the fingers, leads one to suppose that these birds 

 were not expert flyers. They, no doubt, indulged in occa- 

 sional fUghts of short duration ; but they probably scrambled 

 up to perching-places on the trees by the aid chiefly of their 

 legs and wing-claws. They must have been much persecuted 

 by reptiles ; for all new modes of hfe are sure to meet with 

 violent opposition from the " authorities " of the time. 



Mammals had now been long in existence ; and doubtless mammals 

 had greatly increased in number ; but they do not seem to 

 have been much larger than their mouse- and rat-sized 

 ancestors. Some, to judge by their teeth, were primitive 

 insectivores, and may have been forerunners of moles {Amphi- 

 therium). Some forms probably did not differ very much 

 from living opossums (Phascolotherium) ; whilst others were 

 apparently developing in the direction of squirrels and other 

 rodents (Plagiaulax, Bolodon, etc.)'. 



Some of the creatures had teeth far exceeding in number 

 those of any living mammals ; but in no case do the teeth 

 indicate carnivorous habits. 



Primitive mammals, therefore, were still in an age of 

 innocence. But times were difficult ; and they probably 

 dwelt for the most part in holes and corners, and on high 

 tree-branches ; and rarely ventured from their retreats save 

 under cover of darkness. 



H 



