266 THE WORLD OF LIFE CHAP. 



Dr. Woodward further remarks : 



"The curious gradual elongation of the face in the Oligocene 

 and Miocene Mastodons can only be regarded as another illustra- 

 tion of the same phenomenon. In successive generations of these 

 animals the limbs seem to have grown continually longer, while the 

 neck remained short, so that the head necessarily became more and 

 more elongated to crop the vegetation on the ground. A limit of 

 mechanical efficiency was eventually reached, and then there survived 

 only those members of the group in which the attenuated mandibles 

 became shortened, leaving the modified face to act as a proboscis. 

 The elephants thus arose as a kind of afterthought from a group of 

 quadrupeds that were rapidly approaching their doom." (See 

 figures in last chapter, p. 229.) 



This last is a specially interesting case, because it is the 

 only one in which, without change of general environment, 

 or apparently of habits, a highly developed animal has 

 retraced its latest steps, and then advanced in a new line 

 of development, leading to the wonderful trunk and the 

 enormous tusks of the modern elephant, as explained in 

 Chapter XII. That these have now attained the maximum 

 of useful growth is indicated by the fact that among the 

 extinct forms are those in which they are developed to an 

 unwieldy size, as in Elephas ganesa of North-West India, 

 whose slightly curved tusks, sometimes nearly 10 feet long, 

 must have put an enormous strain upon the neck, and the 

 mammoth, whose greatly curved tusks were almost equally 

 heavy. 



Excessive Development of Loiver Animals before Extinction 



My friend Professor Judd has called my attention to 

 the fact that many of the lower forms of life exhibited 

 similar phenomena. The Trilobites (primitive crustaceans), 

 which were extremely abundant in the Palaeozoic rocks, in 

 their last stages " developed strange knobs and spikes on 

 their shells, so that they seemed to be trying experiments in 

 excessive variation." 



told by Messrs. Nicholson and Lydekker (Manual of Palaeontology, ii. p. 1449) that 

 the upper carnassial tooth (the fourth premolar) "has four distinct lobes, and is thus 

 the most complex example of this type of tooth known." The canines were about 

 9 inches long (more than half the length of the whole skull), and very massive 

 in proportion. It became extinct in South America in the Pleistocene period, 

 about the same time as the last of the European species. 



