The geographical distribution of animals, with a study of the relations ...

150 DISTRIBUTION OF EXTINCT ANIMALS. [part ii.time since these changes took place is, geologically, minute.The time of the whole of the Post-Pliocene period, as measuredby the amount of physical and general organic change known tohave taken place, is exceedingly small when compared with theduration of the Pliocene period, and still smaller, probably, ascompared with the Miocene. Yet during these two periods wemeet with no such break in the continuity of the forms of life, nosuch radical change in the character of the fauna (though thenumber of specific and generic changes may be as great) as wefind in passing from the Post-Pliocene to recent times. Forexample, in Central Europe numerous hysenas, rhinoceroses, andantelopes, with the great Machairodus, continued from Mioceneall through Pliocene into Post-Pliocene times ; while hippopotamiand elephants continued to live through a good part ofthe Pliocene and Post-Pliocene periods,—and then allsuddenlybecame extinct or left the country. In North America there hasbeen more movement of the fauna in all the periods ; but wehave similar great felines, horses, mastodons, and elephants, inthe Pliocene and Post-Pliocene periods, while Rhinoceros is commonto the Miocene and Pliocene, and camels range continuouslyfrom Miocene, through Pliocene, toall alike became extinct. Even in South America the evidence is,as far as it goes, all the same way. We find Machairodus, Equus,Mastodon, Megatherium, Scelidotherium, Megalonyx, and numerousPost-Pliocene times ;—whengigantic armadillos, alike in the caves and in the stratifiedtertiary deposits of the Pampas ;— yet all have since passed away.It is clear, therefore, that we are now in an altogetherexceptional period of the earth's history. We live in a zoologicallyimpoverished world, from which all the hugest, and fiercest,and strangest forms have recently disappeared ;and it is, nodoubt, a much better world for us now they have gone.Yet itis surely a marvellous fact, and one that has hardly been sufficientlydwelt upon, this sudden dying out of so many largemammalia, not in one place only but over half the land surfaceof the globe. We cannot but believe that there must have beensome physical cause for this great change ; and it must havebeen a cause capable of acting almost simultaneously over large