236 



EVOLUTION AND GENETICS 



animals were sluggish creatures, and were well protected by their 

 bony plates in such encounters as they must have had. Such 



Fig. 143. — Restoration of the dinosaur, Triceratops. Length 20-25 feet. 

 Upper Cretaceous of western North America. (From Lull.) 



modern species as the alligators are no mean illustrations of pro- 

 tective armor, but the armadillo is among the best (Fig. 144). 



Fig. 144. — Nine-banded armadillo, Tatii novcmcinctus. (Through the courtesy 

 of the New York Zoological Society.) 



These little mammals are so completely covered with bony dermal 

 plates that when they roll into a ball little else is exposed. 



Speed. This quality as an adaptation is too well known to need 

 discussion. It is conspicuous in such animals as the horse and 

 deer as a primary protective adaptation. 



