320 PRINCIPLES OF ANIMAL BIOLOGY 



America; Mastodon from the Pliocene and Pleistocene of North America, 

 Europe and Asia; Stegodon from the Pliocene of southern Asia; and Elephas 

 from the Pleistocene of the Americas, Europe and Asia, as well as the 

 living elephants of Asia and Africa. A study of Fig. 218 in connection 

 with the following account will disclose the more striking steps of evolu- 

 tion. These forms differed from one another in a number of features, but 

 the differences between any member of the series and the one that pre- 

 cedes or that which follows were so small that the series is obviously a 

 continuous one. Moeritherium was very different from the modern ele- 

 phant, but the intermediate forms completely bridge 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. 218, F') composed of some- 

 what cancellate bone, that is, bone containing open spaces; the elongation 

 of the second pair of incisors in each jaw to form short tusks; the indica- 

 tion of transverse ridges on the molar teeth (Fig. 218, F); and the posi- 

 tion 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. Palaeomasto- 

 don was of somewhat larger size than the preceding form, the posterior 

 part of the skull was distinctly higher (Fig. 218, £") with a greater de- 

 velopment 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 {E) 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, which is believed to indicate 

 the existence of a short proboscis extending at least to the tips of the 

 tusks. 



