The science of life : fully illustrated in tone and line and including many diagrams

THE EVIDENCE FROM LIVING THINGS

Fig. 144. Some extinct South American Mammals of the later Cenozoic Period (V), as they probably looked when alive.

Top left: Macrauchenia, one of the Litopterns.

was bulky and tall, and probably browsed on the branches of trees. This creature closely resembled the existing sloths in its anatomy, but lived on the ground and must have weighed Toxodon, a large herbivore of a unique type. af another exclusively South American group of herbivores. Bottom left:

Sloth. over a ton.

Top right :

Unlike most of its relatives, which took to a horse-like life, this animal

Top centre: Megatherium, the Giant Ground

Bottom right: Pyrotherium, representative A form of Glyptodont, very similar in

construction to a large armadillo, but with carapace all in one piece, and a knob of heavy spikes on the end of its tail,

which it doubtless used as a club.

lower sub-classes of mammals, the pouched marsupials and the egg-laying monotremes. In point of fact, no egg-laying mammals occur outside this area, and no marsupials, except the American group of opossums, and one curious little creature called Coenolestes, with teeth in some ways recalling those of kangaroos, from South America. All the rest are Australian—kangaroos and wallabys, cuscuses and phalangers, wombats and bandicoots, marsupial wolf and Tasmanian devil, pouched ant-eaters and pouched moles and pouched mice—some forty genera, with hundreds of species. Add to this the Platypus and its egg-laying confréres, the spiny anteaters, and you have indeed a strange zoo. _ Now, it might naturally be supposed, and in the past often was assumed, that each Species and each group lived in the region best suited to it. But such is demonstrably and obviously not the case. New Zealand has no native mammals save a bat or two and possibly one species of rat—and yet introduced mammals thrive and multiply. Rabbits, for instance, have run wild over

Lower right-hand corner: Outline of a collie dog, to give the scale.

large areas, and red deer introduced from Scotland have not only thriven, but have grown much larger than they ever do in their native land. Then the house-sparrow has spread and the starling is spreading over the whole of North America, in spite of the competition of the hundreds of kinds of native birds. The few horses introduced by the Spanish conquerors of South America multiplied and ran wild in huge herds over the pampas. Far from the native Australian birds and animals being especially well adapted to Australian conditions, they are no match for the species that have been introduced from other regions. The mere mention of rabbits will make an Australian farmer cross. And when we come to plants we find that one of the gravest problems of agriculture in various countries, notably New Zealand and Australia, is to prevent introduced species like the prickly pear and blackberry from overrunning the country and ousting not only the native plants, but man and his agricultural efforts as well. Why then are whole groups of related

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