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

158 EXTINCT ANIMALS OF AUSTRALIA. [part ii.tion could have occurred in a country like Australia ; but if theocean sank 2,000 feet, the great eastern mountain range mighthave given rise to local glaciers. It is, however, almost certainthat during late Tertiary times Australia must have been muchmore extensive than it is now. This is necessary to allow of thedevelopment of its peculiar and extensive fauna, especially as wesee that that fauna comprised animals rivalling in bulk those ofthe great continents. It is further indicated by the relationswith New Guinea, already alluded to, and by the general characterof the various faunas which compose the Australian region, detailsof which will be found in the succeeding part of this work.The lowering of the ocean during the Glacial period would befavourable to the stillfurther development of the fauna of sucha country ; and it is to the unfavourable conditions produced byits subsequent rising—equivalent to a depression of the land tothe amount of two thousand feet—that we must impute theextinction of so many remarkable groups of animals. It is notimprobable, that the disappearance of the ice and the consequent(apparent) subsidence of the land, might have been rapid ascompared with the rate at which large animals can becomemodified to meet new conditions. Extensive tracts of fertileland might have been submerged, and theconsequent crowdingof large numbers of species and individuals on limited areaswould have led to a struggle for existence in which the lessadapted and less easily modifiable, not the physically weaker,would succumb.There is, however, another cause for the extinction of largerather than small animals whenever an important change ofconditions occurs, which has been suggested to me by a correspondent,1 but which has not, I believe, been adduced by Mr.Darwin or by any other writer on the subject. It is dependenton the fact, that large animals as compared with small ones arealmost invariably slow breeders, and as they also necessarilyexist in much smaller numbers in a given area, they offer farless materials forIn such an extreme case as thatfavourable variations than do smaller animals.1Mr. John Hiekman of Desborongh.of the rabbit and elephant, the