THE EOCENE OF EUROPE AND NORTH AMERICA 



125 



Fig. 39. — Skeleton of the Lowei- Eocene cotidylarth Aleni- 

 scotherium ten-aeriihrce. In the American Museum of Natural 

 History. (N^.B. The scapula is only partially restored.) 



complete skeleton of P. prifucrvus with its five digits on the fore and hind 

 feet and its primitive bunodont teeth was welcomed as realizing the proto- 

 type or atavus of the Ungulata; but more profound study has revealed that 

 this extremeh^ small-brained (Fig. 40), long-tailed animal, replete with 

 archaic unguiculate 

 characters, is not the 

 ancestor of a new and 

 vigorous stock, but the 

 survivor of a dying-out 

 stock. Like its am- 

 blj-pod contemporaries, 

 the Wind River species, 

 P. wortmani was less 

 abundant and of dimin- 

 ished size. A contem- 

 porary condvlarth of 

 the proportions of a 

 modern hyrax is Menis- 

 cotherium (Fig. 39), with its very complex bunolopho-selenodont grinding 

 teeth and reduced cropping teeth. 



The heavy-limbed Amblypoda of the period include several species of 

 Coryphodon, attaining the proportions of small rhinoceroses, with crested 

 grinding teeth and defensive canine tusks. These animals were termed 

 Pantodonta by Cope, in reference to the complete series of upper and lower 

 incisors. They have a rather feebly developed chest and musculature of 

 the luml^ar region, abbreviated tail, short, clmiisy feet, and may have been 

 partly amphibious in habit. The skull marks a great advance upon that 

 of the ancestral Pantolamhda, and rudiments of the posterior pair of osseous 

 horns, characteristic of the succeeding genus Uintatherium, are observed. 



Anew order (Tillodontia) of gnawing diprotodont phytophagous placentals 

 is heralded in species of Esthonyx, in which one pair of the incisor teeth is 

 beginning to enlarge at the expense of the others, prophetic of the fully di- 

 protodont Tillotherium of the Middle Eocene. The supposed aberrant 

 Edentata of the order Taeniodonta, or Ganodonta, succeeding the Torrejon 

 Stylinodontidse, are now represented by the still more progressive Cala- 

 modon, \\\i\i a deep-set pair of anterior teeth and still more reduced enamel 

 on the grinding teeth. The tendency of these herbivorous forms to become 

 diprotodont, or enlarge a pair of front teeth, is thus manifested independently 

 in two orders. The Insectivora are now represented by three and perhaps 

 four families, namely, the pantolestids (Palceosinopa) , believed to be long- 

 tailed aquatic forms analogous to the potamogalids of modern Africa; 

 the leptictids (Palceidops) , probably terrestrial forms of the size of the 

 hedgehog {Erinaceus) ; the hyopsodontids (Hyopsodus), with teeth like 

 those of Eohippus on a miniature scale, animals which were long regarded 



