THE -CENOZOIC AGE. 213 



cms period are unknown. If the period of transformation was the 

 preceding Laramie period, which is regarded by Hayden as a 

 transition group between the Cretaceous and Tertiary; then the ev- 

 olution of their forms occurred elsewhere, where no records have, 

 been preserved. It probably, however, was near by, and may have 

 been the region of the plains in Kansas and Nebraska; and if so, 

 during the early Eocene they came by migration around the shores 

 of the Vermillion lake, in whose sediments their remains were pre- 

 served. 



The distinguishing peculiarity among the mammals that now 

 appeared in large numbers was the tapiroid features that marked 

 them all. They were mostly odd toed (Perissodactyls}, like birds 

 and dinosaurs. It has been observed by zoologists that as dinosaurs 

 in the character of the sacrum, vertebra, ischium, etc., were related 

 to, or had mammallian characters, so the tapiroid mammals of the 

 Eocene had also dinosaurian features. The dinosaurs were still 

 more closely in their organization related to birds, so that it is un- 

 certain of many of them whether they were most reptile or bird. 

 It is possible, therefore, that at some time along the transition pe- 

 riods of the Mesozoic the dinosaurian branch divided, one part pro- 

 ceeding towards or transforming into birds, and the other into the 

 mammalia. 



Among the lower Eocene Vermillion animals Cope has des- 

 cribed three small species of carniverous animals, having more or 

 less of the then common tapiroid characters. 



The hoofed (Ungulatd] animals are, however, the most interest- 

 ing. Fifteen species of these are from this group. Six of them be- 

 long to the famous Dawn Horse Family (Eohippus), and have 

 been described mainly by Marsh. They w r ere about the size of a 

 fox, and had three toes on the hind foot and five on the front, four 

 of which were serviceable, and one splint (metacarpei) that did not 

 touch the ground, but probably carried a rudimentary thumb toe, 

 " like a dew claw." Unlike the modern horse, " the bones of the 

 leg and forearm were not yet distinct." (Marsh.) 



The Vermillion beds from which these animals were procured 

 have been called \h&Cary,phodonbeds^ from the presence of remains 

 of animals that have received that designation. These peak-toothed 

 animals (Caryphodons^ of which four species have been described, 

 were peculiar in their highly generalized type of foot and tooth 

 structure. They had five hoofed toes, and their general structure 



