CHAPTER IV 



THE DAWN OF MAMMALIAN LIFE 



The animals that we considered in the last chapter, thougli show- 

 ing certain unmistakable likenesses to the mammals, are never- 

 theless unquestionably not mammals but reptiles. In the 

 Triassic strata, however, we first meet with the remains of 

 undoubted mammals. The Mammalia first appeared upon the 

 earth in a tentative and hesitating way : they had not cast off 

 many of the characters of their supposed reptilian forefathers ; 

 they shrank from observation and destruction by their small size, 

 and apparently, so far at any rate as their teeth aiford a clue, by 

 an omnivorous diet. The world abounded at that period in large 

 and carnivorous reptiles, which may indeed have been the 

 principal enemies with which the first mammals had to cope. 

 These early mammals lingered on to so late a period as the 

 Eocene ; but the majority of the genera were Triassic, Jurassic, 

 and Cretaceous. Certain of the primitive mammalian forms have 

 been referred to the Marsupials, and their resemblances to the 

 Monotremata have also been pointed out. The current view of 

 the present time, however, is that they form a special order, 

 which may possibly have embraced the ancestors of both 

 Marsupials and Monotremes ; for it is reasonable to explain in this 

 way the combination of characters of these two orders which they 

 present. For this group the name Allotheria has been proposed 

 by Marsh, and Multituberculata by Cope ; the latter term is the 

 less suitable, in that the Monotremata {Ornithnrhynchus) are also 

 " multituberculate." The group is known in a very imperfect 

 fashion. The remains are but few and fragmentary ; and for the 

 most part we have only a few teeth to speculate upon. This is 

 natural enough, for the harder teeth might easily be supposed to 



