As a general mark of affinity with mammals the reduction of the intercentra in _Cynognathus_ may be noted, and also the existence of a small though perfectly obvious obturator-foramen, separating the pubis from the ischium. There are further details {95} which tend in the same direction. And we shall probably not go far wrong in the present state of our knowledge if we assign the origin of the mammals to some type which would be included in the order Theriodontia or at least in the sub-class Theromorpha. * * * * * {96} CHAPTER IV THE DAWN OF MAMMALIAN LIFE The animals that we considered in the last chapter, though showing certain unmistakable likenesses to the mammals, are nevertheless 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 afford 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 (_Ornithorhynchus_) 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 {97} have resisted the decay which would more readily affect the softer bones. Where there are bones it is frequently the lower jaw alone which has been preserved for us--a bone which has also been preserved in the case of some of the contemporary Marsupials.