Chap. 35 REPTILES FIRST LAND VERTEBRATES 723 



by horny scales. They are seemingly dull and slow but are capable of lightning 

 quick attacks (Fig. 35.1 1 ). In past ages, they were widely distributed into the 

 cooler regions. Now they are restricted to the tropics and semitropics. In 

 relatively few years excess hunting for eggs, young animals, and skins valued 

 for leather have dangerously decreased the alligators and crocodiles in Florida 

 and other southeastern states. 



Crocodilians are without exception amphibious. They float partly submerged 

 in quiet, warm waters, but true to the habit of their group they lay their eggs 

 on land. They are all carnivorous, the young ones feeding upon fishes, the 

 older ones upon water birds and mammals. They have pointed teeth and under 

 jaws with a spring like a steel trap, capable of easily crunching the bones of a 

 dog. The feet are little used in swimming but the side-swinging of its powerful 

 tail sends an alligator rapidly through the water. The heart is four-chambered, 

 the right and left ventricles being separated in crocodilians, but in no other 

 reptiles. The urinary bladder is absent as it is in birds. 



Alligators and crocodiles are essentially similar but the differences between 

 them are sufficient to place them in separate genera, the two American ones 

 being Alligator and Crocodilus. The most obvious difference in these two is 

 in the shape of the head: in alligators broad with a blunt snout; in crocodiles 

 narrow with a pointed snout (Fig. 35.11), Alligators are hardier, can live 

 farther north than crocodiles, and are able to hibernate under water as turtles 

 do. Crocodiles are practically helpless in water at 45° F. and soon drown. 



Fig. 35.11. Left, head of alligator, blunt snout. Right, head of crocodile, pointed 

 snout. (Courtesy, Rand: The Chordates. Philadelphia, The Blakiston Co., 1950.) 



