304 UNDERWATER GUIDE TO MARINE LIFE 



ing vertebrate group has lasted more or less unchanged as long as turtles have. 

 The life span of turtles is not precisely known, but they are probably the most 

 long-lived of all animals, surpassing ages of 100 to 150 years. 



SEA TURTLES: Family Cheloniidae 



Sea turtles probably arose from marsh-dwelling, primitive shelled turtles as 

 long ago as the Triassic Period (over 150 million years ago). They live in the 

 sea but betray their role as converted land animals by breeding on land and by 

 breathing air. Their feet have turned to flippers, and the manner of propulsion 

 is different from fresh-water aquatic turtles since the flippers are not used as 

 paddles but as "wings." They literally fly through the water. This is an efficient 

 mode of progression since these turtles are able to cover 100 yards in 10 seconds 

 and thus qualify as the speediest of reptiles, with the possible exception of some 

 desert lizards. (The leatherback turtle, of a different family, is probably even 

 faster than these.) On the fore-flippers of the male is a single claw used to grasp 

 the female during copulation. This claw can inflict a painful wound on the 

 unwary. Males also have a long tail. 



For all turtles, enclosure within a shell poses a respiratory problem. Since the 

 lung cannot expand within a rigid box, the exposed areas of skin around each 

 of the four legs act as little diaphragms, expanding for inhalation. But in the 

 case of sea turtles, the shell has been somewhat reduced, and the plastron has 

 a longitudinal hinge which does, in fact, allow the chest to expand so that great 

 quantities of air can be inhaled for prolonged submersion. The authors have 

 held young hawksbill turtles in their hands and have found this accordionlike 

 expansion to be marked on inhalation. 



Sea turtles come onto land to lay eggs and thus expose themselves to the hard- 

 ships there, particularly the danger of that rapacious carnivore, man. In the late 

 spring and summer primarily (some sea turtles breed the year around), the 

 females, heavy with eggs, drag themselves onto a sandy shore. There, above the 

 high-water mark, a neat little hole is delicately dug with the hind flippers and 

 up to three hundred eggs are laid, a record for turtles. Then the hole is filled 

 in, and the fore-flippers aid in generally disturbing a large area of sand so that 

 the exact location of the nest is obscured. During the whole time, the mother's 

 eyes secrete tears profusely as if the whole project were breaking her heart, but 

 this wetness is probably only to protect the eyes, which are accustomed to salty, 

 aqueous surroundings. Then she drags herself, exhausted, back to the sea. The 

 young, only an inch or so in carapace length, hatch at summer's end and head 

 away for a precarious life at sea, where mortality is high. They are eaten by 

 crabs, sea birds, and fishes. At these egg-laying periods, the females are often 

 caught, and eggs are confiscated by man. Large numbers of turtles are also netted 

 or speared at sea. The result has been the decimation of a valuable food source. 

 It will probably take international treaty to save at least one species, the green 

 turtle, from eventual extermination, for modern freezing methods have increased 

 the demand for them. Turtle populations in their present state could not stand 

 concentrated fishing. However, restored to former abundance and with proper 

 conservation, the sea turtles could once again become an important and valuable 

 food source. 



There are only four genera of sea turtles, all of world-wide distribution in 



