THE AUSTRALIAN MUSEUM MAGAZINE. 



67 



Young Native Bear or Koala; an expert tree 

 climber, though rather slow of movement. 



I'lioto. (i. ('. Clutton. 



animal class has its modest beginning, 

 mostly in the distant geological past. 

 Thus the earliest mammals were pro- 

 bably insect-eaters, and were provided 

 with sharp needle-like teeth, adapted 

 for piercing the integument of insects 

 and the bodies of worms. But 

 as time went on these primitive 

 mammals branched out in vari- 

 ous directions and occupied dif- 

 ferent "spheres of intiuence," 

 each group becoming adapted 

 for a specialised mode of life. 

 Thus some took to the vrater and 

 became modified for an aquatic 

 existence, others got the habit 

 of climbing trees and became 

 arboreal like the squirrels or 

 the native bear, still others be- 

 came burrowers. Others again 

 ac(|uired long legs and became 

 swift runners, like the northern 

 wolf or the Tasmanian tiger. 

 "With these changes in the mode 

 of progression were associated 

 changes in the teeth and the 

 digestive system. Animals 



which live on grass have 

 the grinding type of teeth with 

 broad crowns, like tliose of 



the horse and the cow, while the flesh- 

 eating animals, carnivores like the wolf 

 and the lion, have long, sharp teeth 

 with which to grasp their prey, and cut- 

 ting teeth to tear the flesh from the 

 bones of their victims. Before mam- 

 mals had become the dominant race, the 

 reptiles, which were then the lords of 

 ci-oation, had developed in just the same 

 manner, and in just the same directions 

 as the mammals of to-day. There were 

 grass-eating reptiles, which occupied the 

 place of the herbivorous mammals, there 

 Avere carnivorous reptiles, the lions and 

 tigers of their day, huge reptiles wal- 

 lowed in primeval rivers like the present- 

 day hippoiDotamus, and still others roam- 

 ed the ocean like our whales and dol- 

 phins. In this connection one may say 

 with truth that nature abhors a vacuum 

 and fills it with such material as is 

 available. This modification of one 

 class of animals to fit into various en- 

 A'ironments is what is meant by adap- 

 tive radiation, and it is because the mar- 

 sujiials illustrate this great principle in 

 sucli a wonderful manner that they are 

 so interesting, and important to the zoo- 

 logist and student of evolution. 



Banded Ant-Eaters are primitive animals of great 



zoological interest, which are rapidly nearing 



extinction. 



Photo — A. Miisgjrave. 



