THE ANIMAL CLIMAX-THE CHORDATES 



325 



Fig. 13-43. Tuatara (Sp/ienodon) from New Zealand. A "living fossil.' 



world and are often hunted for their 

 valuable hides. These animals show some 

 anatomical features which place them 

 among the highest reptiles. For example, 

 they have a nearly completely divided 

 ventricle in the heart, resulting in a four- 

 chambered heart like that of birds and 

 mammals. They also possess the mammalian 

 characteristic of a nearly complete dia- 

 phragm, which is a muscular separation be- 

 tween the chest and abdominal cavities. 



Another interesting characteristic of these 

 large reptiles is that their scales do not 

 overlap, but instead consist of plates placed 

 upon dermal bones. The resulting very 

 heavy protective armor is resistant to 

 almost any attack of modern animals. 



The turtles 



These are the most odd looking of all 

 reptiles (Fig. 13-45). If they were extinct 

 man would regard them with wonder, but 



Fig. 13-44. American alligator (A//igofor mhsissippiensis). These grow to 16 feet in length. 



