78 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



A study of Figure 5 in connection with the following account will dis- 

 close the more striking steps of evolution. These forms differed from 

 one another in a number of features, but the differences between any 

 member of the series and the one that precedes or that which follows 

 were so small that the series is obviously a continuous one. Moerithe- 

 rium was very different from the modern elephant, but the inter- 

 mediate forms completely bridged the gap. The series exhibits an 

 enormous increase in size of body, changes in the form and size of 

 the teeth, a reduction in the number of teeth, an alteration in the 

 method of tooth succession, the enlargement of certain teeth to 

 become tusks, the elongation and subsequent shortening of the 

 lower jaw, the development of the upper lip and nose into a proboscis, 

 and an increase in the height of the skull through the development 

 of large cavities in the substance of the • bone. These features are 

 described in the several forms seriatim. 



Moeritherium. — The earliest animal recognized as belonging to 

 the elephant series, Moeritherium by name, was recovered from the 

 late Eocene and early Oligocene deposits of northern Egypt. 

 It was slightly over three feet in height. The features suggesting 

 elephantine affinities are the high posterior portion of the skull (Fig. 

 S, F); composed of somewhat cancellate bone, that is, bone containing 

 open spaces; the elongation of the second pair of incisors in each jaw 

 to form short tusks; the indication of transverse ridges on the molar 

 teeth (Fig. 5, F) ; and the position of the nasal openings some distance 

 back of the tip of the upper jaw, indicating probably a prehensile 

 upper lip. There were 24 teeth, and the neck was long enough to 

 enable the animal to put its head to the ground. It probably fed 

 upon tender shoots and swamp vegetation. 



Palaeomastodon. — This form also lived in Egypt, but has recently 

 been found in India. It dates from early Oligocene time. Palaeo- 

 mastodon was of somewhat larger size than the preceding form, the 

 posterior part of the skull was distinctly higher (Fig. 5, E') — with a 

 greater development of cancellate bone, and the neck was somewhat 

 shortened. The upper incisors of the second pair were more elongated 

 as tusks and bore a band of enamel on their front surfaces. The lower 

 second incisors were present, but not enlarged. All other incisors and 

 the canines had disappeared. The molar teeth (£) resembled those 

 of Moeritherium but were larger. The lower jaw was considerably 

 elongated, and the total number of teeth was still high (26). The 

 nasal openings had receded until they were just in front of the eyes, 



