288 



SUBPHYLUM VERTEBRATA: 



two species of coral snakes. The pit viper family is 

 represented by the cottonmouth or water moccasin, 

 the copperhead, and about fifteen species of rattle- 

 snakes. The pit vipers are named for a remarkable 

 sensory structure they possess. This structure, the 

 pit, is found between the nostril and eye and is larger 

 than the nostril. It is a heat and infrared light recep- 

 tor, that locates prey by detecting temperature dififer- 

 ences as small as 1°F between the snake's body and 

 surroundings. 



There should be no doubt about the danger of 

 rattlesnake bites. People die every year in the United 

 States from such bites. However, certain rattlesnakes 

 probably secrete insufficient venom for their bites to 

 prove fatal, and proper treatment of any bite almost 

 always prevents death. Because proper treatment is 

 necessary, anyone likely to contact these animals 

 should be familiar with correct treatment. The best 

 source of such information can be found in a monu- 

 mental work, Laurence M. Klauber's "Rattlesnakes, 

 their habits, life histories, and influence on mankind," 

 a 1956 publication of the University of California 

 Press. Finally, do not have the false sense of security 

 that rattlesnakes do not bite before they rattle. 

 Many an individual has stepped on either a sleeping 



or cold rattlesnake and some of these individuals were 

 bitten without the snake's ever having rattled. Also, 

 many people have observed rattlesnakes watching 

 them and later got these snakes to strike at a stick, 

 all without the snake's rattling. 



ORDER CROCODILIA(= LORICATA) (Crocodilians) 



Diagnosis: lizard-like; jaws with teeth; anus a 

 longitudinal slit; sexes separate, eggs laid; fresh- 

 water, somewhat terrestrial, semimarine (Figure 

 16.23). 



Crocodilians are now represented by over twenty 

 species in three families, the crocodiles, the alligators 

 and caimans, and the gavials. Although the young 

 crocodilians might be confused with some lizards, 

 there is a simple way to distinguish between the two 

 groups. Crocodilians have the anus in the form of a 

 longitudinal slit; lizards, in a transverse slit. Among 

 the largest crocodilians now living are the two United 

 States forms, the American alligator which once was 

 sufficiently undisturbed by man to grow to a length of 

 about 20 feet, and the American crocodile which once 

 grew to about 23 feet. Few of these animals now grow 

 more than 10 feet long in the United States. How- 



Figure 16.23 A crocodilian, Crocody/us (to 23 feet long). 



