346 MAMMALIA. 



latter animal is represented by its typical dentition in the Cromer Forest 

 Bed, and survived in Britain so late as the seventeenth century. The 

 largest known pigs are those whose remains occur in the Lower Pliocene 

 (Siwalik Formation) of India (S. titan and S. giganteus) ; and those with 

 the most complicated molars are also found in this formation (S. falconer i) 

 and in the Pliocene of Algeria (S. phaoochcer aides). The hinder molar in 

 the last-mentioned forms makes some approach to that of the existing 

 African wart-hog (Phacochoerus}, whose ancestry still remains unknown. 



Dicotyles. The peccaries now living in the warmer parts of the 

 American continent are, so far as their dentition is concerned, survivors 

 of very primitive suillines. Their skeleton is specialized only in the feet, 

 the metapodials in and iv being fused together at their upper end, while 

 digit no. v has disappeared from the hind foot. The stomach, however, is 

 also highly specialized, almost approaching that of the ruminants in 

 complexity. Nothing is known of the ancestry of these animals, the only 

 fossil remains hitherto discovered being of Pleistocene age and from the 

 region they still inhabit. 



The Hippopotamidae, now confined to Africa, are remark- 

 ably primitive in most parts of their skeleton, but highly 

 specialized in the front half of the jaws. The grinding teeth 

 have somewhat deepened crowns, and their cusps exhibit a 

 trefoil-shaped section when worn ; the canines and incisors 

 grow from persistent roots. Four stout functional digits are 

 retained on each foot. The ancestry of the hippopotamus is 

 still quite unknown, and the earliest fossils hitherto discovered 

 are only slightly more generalized in the character of their 

 incisors. The genus, so far as known, appears first in the 

 Lower Pliocene (Siwalik Formation) of India and Burmah, 

 where it is represented by species (H. sivalensis and H. irava- 

 ticus) with six incisors of uniform size (fig. 198). These forms 

 may be referred to a sub-genus Hexaprotodon, which also 

 occurs in the Pliocene of Algeria. In the Pleistocene of India 

 there is a species (H. palceindicus) intermediate between the 

 earlier hexaprotodont and the existing African tetraprotodont, 

 H. amphibius; while during the later Pliocene and Pleistocene 

 periods the last-mentioned species, or a very closely related 

 form, wandered over the greater part of southern and middle 

 Europe. In Britain the hippopotamus occurs first in the 

 Cromer Forest Bed, and is found in Pleistocene formations as 

 far north as Yorkshire. Remains of a particularly large herd 



