RULERS OF THE ANCIENT SEAS 59 



the habits of a creature in which the tail so 

 obviously wagged the dog and whose articula- 

 tions all point to great freedom of movement 

 up and down. This may mean that it was an 

 active diver, descending to great depths to 

 prey upon squid, as the Sperm-Whale does 

 to-day, while it seems quite certain that it 

 must have reared at least a third of its great 

 length out of water to take a comprehensive 

 view of its surroundings. And if size is any 

 indication of power, the great tail, which ob- 

 viously ended in flukes like those of a whale, 

 must have been capable of propelling the beast 

 at a speed of twenty or thirty miles an hour. 

 Something of the kind must have been needed 

 in order that the small head might provide food 

 enough for the great tail, and it has been sug- 

 gested that inability to do this was the reason 

 why Zeuglodon became extinct. On the other 

 hand, it has been ingeniously argued that the 

 huge tail served to store up fat when food was 

 plenty, which was drawn upon when food be- 

 came scarce. The fur seals do something sim- 

 ilar to this, for the males come on shore in 

 May rolling in blubber, and depart in Septem- 



