212 



THE MARSUPIALS. 



Further, the wombats are represented by 

 a species which attained the size of a tapir, 

 while the still surviving species are only about 

 equal to a peccary in size. 



But the most remarkable types yielded by 

 the Quaternary strata belong to the family 

 of the kangaroos. Both the kangaroos proper 

 and the rat-kangaroos have left remains in 

 these strata. The genera Protemnodon and 

 Sthenurus, which have been found on the 

 island of Australia, have great similarity to 

 the tree-kangaroos, which at the present day 

 are confined to New Guinea. But the most 

 curious forms are unquestionably Diprotodon 

 and Nototherium. The latter genus has teeth 

 with elevated transverse ridges, like the kan- 

 garoos, the tapirs, and the Dinotherium, but 

 these ridges were very high and sharp. The 

 skull of this animal preserved in the British 

 Museum is upwards of 3 feet in length, and 

 the bones of the limbs give evidence of their 

 having belonged to a long-legged animal with 

 a lower fore-leg capable of being to some 

 extent twisted round like that of the majority 

 of the marsupials of the present day. The 

 lower jaw has a well-marked inflection of the 

 posterior angle. This animal must have been 

 at least as large as an elephant. 



The no less colossal genus Nototherium 

 appears to have had no incisors, and its 

 cheek-teeth perhaps resembled those of Dip- 

 rotodon. In the remains that have come 

 down to us they are unfortunately worn away 

 to such a degree that no conclusion can be 

 drawn as to the form of the crowns. 



We thus see that the Quaternary strata of 

 America and Australia stand in exactly the 

 same relation to the fauna found in the same 

 regions at the present day as the extinct and 

 living placental faunas do to one another in 

 other lands. The extinct genera and species 

 are in general considerably larger than the 

 surviving species. The geographical limits 

 have remained the same, for in America also 

 the Quaternary opossums advanced farther 

 to the north than do those of the present day. 



In the exclusively Australian Quaternary 

 strata only marsupial forms have been found 

 among mammalian remains. If, now, we 

 take into account the fact that at the time of 

 the discovery of Australia, that great island 

 contained in addition to marsupials only a 

 few rare bats and rodents, which were per- 

 haps accidentally introduced by man, and that, 

 moreover, in the Australasian region we meet 

 with some other monodelphian or placental 

 forms only in the districts of Celebes and 

 New Guinea, which are inhabited by a mixed 

 fauna, we are necessarily driven to the con- 

 clusion that the underlying strata can contain 

 nothing but marsupial remains, and that per- 

 haps we shall some day discover in Australia 

 evidences of an evolution such as we find 

 traces of in other regions in the case of pla- 

 cental mammals in Tertiary times. The 

 marsupials of the present day would thus 

 be only the remains of those old faunas which 

 have preserved the marsupial character in 

 Australia through the Cretaceous period, 

 while in other regions of the earth the trans- 

 formation of non-placental into placental forms 

 was accomplished during that geological epoch. 



We may, indeed, be led to such a conclu- 

 sion in another way when we consider that 

 the placental mammals are already repre- 

 sented in the earliest Eocene strata by a 

 certain number of types, which cannot be 

 derived from one another, when we bear in 

 mind further that the Tertiary strata in Europe 

 have hitherto yielded but few remains of 

 marsupials, and that the Cretaceous strata 

 have up to the present day revealed no traces 

 of mammals whatever, and when we remem- 

 ber finally that the oldest known mammalian 

 remains belong mostly, if not exclusively, to 

 the marsupials. 



The genus Peratherium, which is repre- 

 sented by several species in the Upper Eocene 

 of France and England, as well as in the 

 Lower Miocene of Auvergne, is not very 

 different from the opossums of the present 

 day, and may without hesitation be referred 



