DISTRIBUTION OF MAMMALIA IN TIME. 6l3 



cene rocks, is a large form, intermediate between the African 

 Manatee and the Dugong. 



Order V. Cetacea. — The Cetacea, also, are of little geological 

 importance. Remains of Dolphins (Ziphius) and of Whales 

 {Balcenodoii) are found in Miocene deposits ; and numerous 

 ear-bones of Whales occur in the Red Crag of Suffolk (Plio- 

 cene). The most remarkable, however, of the extinct Cetacea, . 

 is the Zeuglodon of the American and Maltese Miocene de- 

 posits. This was an enormous toothed Whale, about seventy 

 feet in length ; but, unlike any of existing Cetaceans, it had 

 the posterior teeth implanted by two distinct fangs or roots. 

 By Owen, Zeuglodon is regarded as the type of a distinct family, 

 intermediate between the Cetacea and the Sirenia. In Sauro- 

 cetes, a large Cetacean from the Tertiary beds of Buenos Ayres, 

 there were double-fanged teeth with conoid crowns. It was 

 much smaller than T^uglodon. 



Order VI. Ungulata. — The hoofed Mammals are repre- 

 sented in past time by so many extinct forms that it will be 

 wholly impossible here to do more than merely allude to some 

 of the more important genera. 



The earliest-known Ungulates occur in the Eocene rocks, 

 where the order is represented by very numerous and interest- 

 ing forms, the more important of which are Pliolophus, Palceo- 

 therium, and Aruiplotherium. 



Of the section of the Ungulates comprising the living Horse, 

 Zebra, and Ass {Solidungula), the earliest fossil example is the 

 Anchitherium of the Lower Miocene, and this was succeeded 

 by the Hipparion of the Miocene rocks. This genus differed 

 from the existing Equidce in the presence of two small toes 

 with hoofs, one on each side of the single functional toe, 

 which alone remains .in living horses. In the Pliocene period 

 appear, for the first time, remains of horses which, like the 

 present form, possessed only a single toe encased in a single 

 hoof. It is interesting to observe that one of the Pliocene 

 horses {Equiis curvidens) occurs in South America; though 

 this continent certainly possessed no native horse at the time 

 of its discovery by the Spaniards. About twenty horses — one 

 of them standing no more than two and a half feet in height — 

 have been described from North America, in which continent 

 no indigenous horse existed at the time of its discovery. 



Of the R/imoceridcB,a. hornless species {Acerotherium) occurs in 

 Miocene and Pliocene strata ; but the best;known fossil species 

 is the two-horned woolly Rhinoceros {Ji. Uchorhiims). This 

 curious species occurs in Post-pliocJene deposits, and must have 

 ranged over tlie greater part of Europe. It was adapted to a 



