RULERS OF THE ANCIENT SEAS 65 
that might almost have swallowed the biggest 
fish of to-day whole, sharks of a size the waters 
had never before contained, and fortunately do 
not contain now. We know these monsters 
mostly by their teeth, for their skeletons were 
cartilaginous, and this absence of their remains 
is probably the reason why these creatures are 
passed by while the adjectives huge, immense, 
enormous are lavished on the Mosasaurs and 
Plesiosaurs — animals that the great-toothed 
shark, Carcharodon megalodon, might well 
have eaten at a meal. For the gaping jaws 
of one of these sharks, with its hundreds of 
gleaming teeth must, at a moderate estimate, 
have measured not less than six feet across. 
The great White Shark, the man-eater, so 
often found in story books, so rarely met with 
in real life, attains a length of thirty feet, and 
aman just makes him a good, satisfactory 
lunch. Now a tooth of this shark is an inch 
and a quarter long, while a tooth of the huge 
Megalodon is commonly three, often four, and 
not infrequently five inches long. Applying 
the rule of three to such a tooth as this would 
give a shark 120 feet long, bigger than most 
