92 LAND MAMMALS IN THE WESTERN HEMISPHERE 



II. The Teeth 



It was pointed out in Chapter II (p. 38) that very often 

 the teeth are all that remains to us of extinct genera and species 

 of mammals, and it may be further noted that the teeth are 

 very characteristic and often suffice to fix the systematic position 

 of a genus. Since, therefore, the teeth play such an uncom- 

 monly important part as fossils and are so pre-eminently useful 

 to the palaeontologist, it is necessary to give some general 

 account of them. 



Among the mammals the teeth display a very great variety 

 of size and form in accordance with the manner in which they 

 are used. Primarily, the function of the teeth is to seize and 

 masticate food, and the kind of food habitually eaten by any 

 animal is well indicated by the form of its teeth. The beasts 

 of prey have teeth adapted for shearing flesh and crushing 

 bones ; plant-feeders have teeth fitted for cropping plants and 

 triturating vegetable tissues; insect-eaters have teeth with 

 numerous sharp-pointed cusps, or it may be, no teeth at all, 

 swallowing without mastication the insects which they capture, 

 etc. Among animals that have similar diet there is very 

 great difference in the form and elaborateness of the grinding 

 apparatus and it is often possible to follow out the steps of 

 evolutionary change, by which, from simple beginnings, a high 

 degree of complexity has been attained. In addition to the 

 uses of the teeth as organs of mastication, they frequently 

 serve as weapons of offence or defence. In the flesh-eaters 

 which capture living prey they are formidable offensive 

 weapons, a^id the fangs of the Lion or the Wolf are instances 

 familiar to every one; but the tusks of the elephants or the 

 hippopotamuses have nothing to do with the taking of prey. 

 Several Old World deer, which have no antlers or very small 

 ones, possess scimitar-like upper tusks, with which they, are 

 able to defend themselves very effectually. 



In the lower vertebrates, such as reptiles and fishes, the 



