RULERS OF THE ANCIENT SEAS 59 
the habits of a creature in which the tail so 
gbviously 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- 
