352 FOLLOW THE WHALE 



of the Pliocene — which lasted from seven million to one million 

 B.C. approximately — this appears to have constituted the complete 

 whale population in the seas and oceans, but we do not know what 

 whales may have lived in rivers or in fresh-water lakes during that 

 time. And this is very important. When we move back into the 

 lower strata of the Pliocene, however, we encounter the remains of 

 two families of whales that are not, at least as far as we know, repre- 

 sented by living examples on the earth today. 



These have been given long Latin names (Acrodelphidae and 

 Hemisyntrachelidae), the first of which may be loosely translated as 

 the "Sharp-fronted Dolphinlike Ones" and the other of which will 

 be ignored because it is not germane to our story. To make matters 

 simpler, I shall refer to the first as the Acrodelphids. They had a his- 

 tory of about fourteen millions of years, according to the dates of 

 the rocks in which their remains have been found, but logic demands 

 that we assume they were around somewhere long before that time. 

 These are very remarkable creatures. 



The Acrodelphids constitute a family of whales somewhere be- 

 tween the ziphioids and the true dolphins of today. They were small 

 animals, about ten feet long, and they retained a number of charac- 

 ters in their skeletons that are regarded as very primitive, notably a 

 completely symmetrical arrangement of the bones of the skull so 

 that one side mirrored the other. As we have seen, modern whales 

 show a great tendency to be lopsided in this respect. What is more, 

 these Acrodelphids had real nosebones, like dogs, ourselves, and 

 other land animals, and their nostrils appear to have been placed far 

 forward on their snouts rather than on the top of their heads like 

 the blowholes of modern whales. Finally, these creatures had loosely 

 connected vertebrae in their necks, so that they must have been able 

 to turn their heads right around, like sea lions. The earliest Acro- 

 delphid, named Argyrocetus patagonicus, found, as its latter name 

 implies, in the southern Argentine in lower Miocene rocks, was about 

 nine feet long and had the most extraordinary upturned snout, un- 

 like any other known mammal, living or extinct, yet another Acro- 

 delphid, named Agabeus, found in association with it had, most sur- 

 prisingly, already lost all its teeth, a condition of affairs that we 

 otherwise regard as a final stage in the evolution of whales. 



Acrodelphids were not by any means the only whales of early 



