THE ANIMAL CLIMAX-THE CHORDATES 



335 



Fig. 13-54. The ostrich is one of the largest flightless birds 



they can be used as 



reaching as much as 12 feet in height, with 

 powerful legs, small heads and rudimentary 

 wings which are useless for flight. They 

 depend on their fleetness for security. An 

 interesting fact is that all modern flisfhtless 

 birds live in regions where there are no 

 carnivores, that is, no members of the cat 

 or wolf tribes. Examples are the ostrich of 

 Africa, the cassowary and emu of Australia, 

 the rhea of South America, and the kiwi of 

 New Zealand. Romer has suggested that 

 these birds once were able to fly but be- 

 cause there were no terrestrial predators 

 that might harm them they simply ceased 

 flying and remained on the ground all of 

 the time, thus conserving their energies for 

 the important job of obtaining food. One 

 reason that birds probably took to the air 

 in the first place was to be better able to 

 flee from their enemies. If the enemies are 

 removed, then the need for flight is no 

 longer present; hence, why fly? 



. Its powerful legs carry it swiftly over the ground, and 

 organs of defense. 



THE CLIMAX ANIMALS: 

 THE MAMMALS 



The dominant and most complex animals 

 on the earth today are the mammals. What 

 was their origin and what characteristics 

 have tliey been able to accumulate that 

 have caused them to outstrip all others, at 

 least temporarily? They are certainly as 

 varied in size, shape, and habitats as any 

 animals that have ever lived ( Fig. 13-55 ) . 

 They seem to have invaded every possible 

 portion of the earth, water, and air, and are 

 reasonably successful in all environments, 

 just how long they can retain the zenith 

 where they now find themselves is a prob- 

 lem for speculation. If they follow the pat- 

 tern of former dominant types they will 

 eventually decline, to be succeeded by 

 some other form which is today, perhaps, 

 an insignificant animal. 



According to the best estimates, the 



