VERTEBRATE LIFE IN AMERICA. 677 



The Sirenians, 1 which appear first in the Eocene of the Old World, 

 occur in the Miocene of our eastern coast, and throughout the later 

 Tertiary. The specimens described have all been referred to the genus 

 Manatus, and seem closely related to our living species. In the Ter- 

 tiary of Jamaica, a skull has been fomid which indicates a new genus, 

 Prorastomus, also allied to the existing manatee. The genus Phytina, 

 once abundant on our Northwest coast, has recently become extinct. 



The Ungulates 2 are the most abundant mammals in the Tertiary, 

 and the most important, since they include a great variety of types, 

 some of which we can trace through their various changes down to 

 the modified forms that represent them to-day. Of the various divis- 

 ions in this comprehensive group, the Perissodactyle, or odcl-toed Un- 

 gulates, are evidently the oldest, and throughout the Eocene are the 

 prevailing forms. Although all of the Perissodactyles of the earlier 

 Tertiary are more or less generalized, they are still quite distinct from 

 the Artiodactyles, even at the base of the Eocene. One family, how- 

 ever, the Coryphodotitidce, which is well represented at this horizon, 

 both in America and Europe, although essentially Perissodactyle, pos- 

 sesses some characters which point to a primitive Ungulate type from 

 which the present orders have been evolved. Among these characters 

 are the diminutive brain, which in size and form approaches that of 

 the reptiles, and also the five-toed feet, from which all the various 

 forms of the mammalian foot have been derived. Of this family, only 

 a single genus, Coryphodon (Pathmodon), is known, but there were 

 several distinct species. They were the largest mammals of the lower 

 Eocene, some exceeding in size the existing tapirs. 



In the middle Eocene, west of the Rocky Mountains, a remarkable 

 group of Ungulates makes its appearance. These animals nearly 

 equaled the elephant in size, but had shorter limbs. The skull was 

 armed with two or three pairs of horn-cores, and with enormous canine 

 tusks. The brain was proportionally smaller than in any other land 

 mammal. The feet had five toes, and resembled in their general 

 structure those of Coryphydon, thus indicating some affinity with that 

 genus. These mammals resemble in some respects the Perissodac- 

 tyles, and in others the Proboscidians, yet differ so widely from any 

 known Ungulates, recent or fossil, that they must be regarded as form- 

 ing a distinct order, the Dinocerata. Only three genera are known, 

 Pinoceras, Tinoceras, and Uintatherium, but quite a number of spe- 

 cies have been described. During the later part of the middle Eo- 

 cene these animals were very abundant for a short time, and then be- 



1 Sirenia, an order of aquatic mammals represented at present only by the manatee 

 and dugong. 



2 Ungulata. As now used, this term is employed to designate that order of mammals 

 which contains the Artiodadyla, or even-toed, and the Perissodactyla, or odd-toed, mam- 

 mals with hoofs. It thus includes, among the former, the camels, giraffe, bovines, ante- 

 lopes, deer, musks, swine, and hippopotami ; and, among the latter, the horses, rhinoce- 

 roses, and tapirs. 



