6i8 



HISTORICAL GEOLOGY 



Fig. 551. - 

 ancestral deer (Lower 

 Oligocene). (After H. F. 

 Osborn.) 



Deer. — There are few, if any, cases in which the changes that 

 the individual undergoes in his growth from birth to old age, so con- 

 spicuously parallel those which his ancestors 

 underwent in the course of their geological 

 history as in the deer. In the development of 

 the existing deer the males and females are 

 born hornless ; at the end of the first year the 

 male acquires a simple, one-pronged antler; 

 this is shed, and at the end of the second year 

 a two-pronged antler is grown ; in the next 

 year the antlers have two or three tines, and 

 so on until the maximum number for the species has been reached. 

 The geological history of the deer agrees in many particulars with 

 the facts of individual development from year to year. The oldest 

 known members of the tribe (Leptomeryx) (Fig. 551) in the Oli- 

 gocene have no horns, as is true of their surviving relatives in Asia. 



The earliest deer with horns 

 (Dicroceras) (Fig. 552 A) of 

 which there is any record 

 lived in the Miocene where 

 the antlers were two- 

 pronged. In the Upper 

 Miocene deer with three- 

 pronged antlers (Fig. 552 B) 

 begin, and in the Pliocene 

 the four-pronged (Fig. 552 

 C) ; then the five-pronged ; 

 and finally, near the close 

 of the Pliocene, a deer ap- 

 pears in which the antlers 

 are extremely branched. 

 The deer first migrated into 

 America after the two- 

 pronged stage had been de- 

 veloped. 



The teeth of the Oli- 

 gocene deer are very short- 

 crowned, but in the course 

 of the Tertiary they become 

 longer and more thoroughly 



Fig. 552. — Horns of deer, showing the evolu- 

 tion of horns. A, two-pronged deer of the Middle 

 Miocene {Dicroceras)', B, the three-pronged horn 

 of the Lower Pliocene deer; C, the four-pronged 

 horn of the Upper Pliocene. (Modified after 

 Dawkins.) 



