338 GENERAL ZOOLOGY 



lower jaw and the structure of its upper jaw indicates that 

 it possessed a short extensile proboscis. No elephant bones 

 are known from Oligocene deposits, but in the Miocene of 

 France a great probocidian, Tetrabelodon, has been dis- 

 covered which is remarkable for the great elongation of the 

 lower jaw and the shortness of the lower tusks (C). In 

 Pliocene times several species of the genus Dibelodon lived 

 in South America. These animals had well-developed 

 tusks in the upper jaw but the short lower jaw was without 

 incisors. The mastodon (D), which lived in North America 

 during glacial times, had the lower jaw still further shortened. 

 Modern elephants (E) apparently took their origin from 

 a straight tusked type, Stegodon, which developed in 

 the Indian region. The genera mentioned are only a few 

 representatives of numerous types of fossil proboscidians. 

 At one time there were elephants in Europe, Africa, Asia, 

 North and South America. From what is known Lull is 

 able to make the following generalizations concerning the 

 racial history of the Proboscidia: 



"The physical changes undergone by the race are also 

 clearly shown, as the palseontological series is very complete. 

 These changes may be thus summarized: Increase in size 

 and in the development of pillar-like limbs to support the 

 enormous weight. Increase in size and complexity of teeth 

 and their consequent diminution in numbers and the de- 

 velopment of the peculiar method of tooth succession. The 

 loss of the canines and of all the incisor teeth except the 

 second pair in the upper and lower jaws and the develop- 

 ment of these as tusks. The gradual elongation of the 

 symphysis or union of the lower jaws to strengthen and 

 support the lower tusks while digging, culminating in 

 Tetrabelodon. The apparently sudden shortening of this 

 symphysis following the loss of the lower tusks and the 

 compensating increase in size and the change in curvature 

 in those of the upper jaw. The increase in bulk and height, 

 together with the shortening of the neck necessitated by the 

 increasing weight of the head with its great battery of 



