584 MAMMALS. 



The genus Mastodon is represented by fossil remains in Miocene, 

 Pliocene, and even in Pleistocene strata, in Europe, India, and America. 

 The molar teeth show transitions between those of elephants and those 

 of other Ungulates. 



In Dinotherium, found in Miocene and Pliocene strata in Europe and 

 Asia, the lower jaw bore an enormous pair of tusks projecting vertically 

 downwards, and all the back teeth seem to have been in use at the 

 same time. 



Several extinct Sub-Orders. 



Although we cannot describe the following remarkable types, it is 

 important to notice their existence, for they serve to impress us with the 

 original connectedness of what are now separate orders. 



The huge Amblypoda, found in Eocene formations in W. America, 

 had three pairs of remarkable protuberances on the top of the skuU, no 

 upper incisors, large upper canines, especially in the males, and six back 

 teeth (f l|g). Example — Uintatherium ; the genus Coryphodon may also 

 be related. 



Cope includes a number of generalised Eocene Ungulates under the 

 title Condylarthra. Some seem ancestral to the Perissodactyla and 

 Artiodactyla ; some suggest a union of ancestral Ungulates and ancestral 

 Carnivores. The genus Periptychus may be regarded as an ancestral 

 Bunodont, and Phenacodus as near the origin of the horse stock. But 

 Phenacodus is so generalised that Cope has suggested affinities between 

 it and not only Ungulates, but also Carnivores and Lemurs. 



The tertiary strata of S. America have yielded a number of strange 

 types, e.g., Toxodon, Nesodon, and Typotherium, ranked in the sub- 

 order Toxodontia and perhaps uniting Ungulates and Rodents. 



From the Eocene of N. America, Marsh has disentombed a group of 

 animals which he calls Tillodontia, e.g., Tillotherium, which seem to 

 combine the characters of the Ungulata, Rodentia, and Carnivora. 



Order 4. Cetacea. 



The Cetaceans, including whales and dolphins and their 

 numerous relatives, are aquatic mammals of fish-like form. 



The spindle-shaped body has no distinct neck between 

 the relatively large head and the trunk, and tapers to a 

 notched tail, the horizontal expansions of which form the 

 flukes. The fore-limbs are paddle-like, and there are no 

 external hints of hind-limbs. Most forms have a median dorsal 

 fin. Hairs are generally absent, though a few bristles may 



