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

BOOK 3 THE SCIENCE OF LIFE CHAPTER 4

animals tied down to limited regions of the of land and water is in no way permanent. world? What meaning is there in the In the past, the main land-masses of the world restriction of the giraffe family to Africa, the have been connected and disjoined in many whole of the edentate order of sloths and other ways; and geology can often tell us armadillos and ant-eaters to Southern just when and where the connections and America, all the monotreme sub-class and partings were made, and what was the dis-

almost all the marsupials to Australia ? tribution of seas and continents during a The answer is to be found in the past, in particular geological period. the history of evolving life in relation to the Animals such as land-mammals can and do

history of the seas and continents. ‘Through migrate slowly until they are spread over the fossils we are able to discover not only the past whole of aland-mass. But there are barriers development of existing groups, but also their which they cannot cross. The sea is the past distribution in each epoch. Geology, most formidable of such barriers, ice-sheets on the other hand, can tell us a great deal are another, and broad deserts may be nearly about the extent of the sea and land in past as bad. ‘Thus, the distribution of any group periods. It can do this by studying wherein of land-animals will depend upon three each epoch marine deposits were laid down, factors—first, upon the region where the where there were deserts, or evaporating group happened to originate ; second, upon inland seas which produced beds of salt, the connections which this region then and where the invading ocean had carved later happened to have with other landbeaches, where ice-sheets had passed or masses; and third, upon the fate of the mountain-ranges had been’ elevated. group in the different regions to which it Through such evidence, geology is able to obtained access.

say definitely that the present distribution If mammals first evolved after New Zea-

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Fig. 145. Some Characteristic Animals from South America.

Top row : Tamandua (Tree Ant-ealer, an animal probably subsisting in the main upon tree-living Termites) ; Hlumboldt's Woolly Monkey (with prehensile tail, like most New World monkeys) ; Great Ant-eater (with huge claws for tearing down the cement-like walls of the nests of ground-living Termites). Centre: Huanaco (related to the Llama) ; | Three-toed Sloth (an animal which spends most of its life hanging upside down from the higher branches of trees ; it aesembles ils surroundings by being coloured green through the growth of a species of single-celled green plant in special crevices in ifs hairs) ; Marmoset (one of the smallest and most primitive of New World monkeys). Bottom row : Nine-banded Armadillo (a type which has spread from South America to the southern United States) ; Opossum (a species in which the young are not carried about in the pouch, but anchored by their tails io the tail of their mother) ; Vizcacha (a large rodent).

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