THE EVOLUTION OF THE ELEPHANT 



lived in Asia in Pliocene time. They were abundant both in 

 numbers and in species. Some of them had enormous tusks, 

 one tusk in the British Museum being nine feet and nine 

 inches long. 



The cross ridges of the teeth continued to develop in num- 

 ber and in height, and to supplement them, the cement, 

 which usually is found only around the roots, worked its 

 way up around the outside and into the valleys between the 

 ridges, until the high ridges were welded together. Such 

 teeth may show from ten to twenty-seven ridges and may 

 reach a height of eight to twelve inches. From the time the 

 valleys are filled with cement these forms are known as true 

 elephants, mammoths if extinct, elephants if living. This 

 increase in the size of the tooth, coming at the same time as 

 the shortening of the jaw, has caused a curious manner of 

 succession in the teeth of elephants. The first (rather small) 

 grinding tooth comes into place soon after birth. It is used 

 and worn for two or three years. Then the second grinder 

 comes up behind it, crowds it out toward the front and takes 

 its place. In a similar manner, one after another, the rest of 

 the grinding teeth come in, crowding out the predecessor, 

 until in about the fifteenth year the last molar, the largest 

 one, comes into position, and this one functions for the rest 

 of the elephant's life, 200 years or so. These true elephants 

 are grazing forms. They flourished in Pleistocene time all 

 over the world except in Australia. In North America, along 

 the ice front, roamed the woolly mammoth, Elephas prmji- 

 genius, mostly about nine feet high, the same mammoth that 

 roamed in northern Europe and Asia and that has been 

 preserved for us, frozen in the ice, in Siberia and Alaska. 

 In southeastern North America there were the Columbian 

 and Jeffersonian mammoths, ranging from eleven to twelve 

 feet in height. In the Southwest lived the imperial mam- 



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