150 EVOLUTION IN THE PAST 



were living in the Oligocene Period, but, so far as is known, 

 they were in a decadent condition. New forms, however, 

 were abroad that in respect of the skull were certainly nearer 

 to the whales of our own time (Squalodon). They were in fact 

 true whales ; but the family is now quite extinct (Squalo- 

 dontida). 



SIRENIANS Sea-cows closely resembling manatees were off the Oligo- 

 cene coasts (Halitherium). They, however, still retained 

 well-defined vestiges of hind-limbs, and differed, therefore, 

 in this respect from living forms. The latter also present a 

 difference in being more numerously toothed ; prolonged life 

 in the seas having, in their case, proved conducive to tooth 

 multiplication. 



BIRDS Bird-life comes before us in the Oligocene shorn of much 

 antique character, and reinforced by many new forms. 

 Compound creatures, awaiting differentiations or extinc- 

 tion were, no doubt, still in existence ; but most of the birds 

 known to be then living resembled more or less closely some 

 of the present-day forms. It must, however, be admitted 

 that the annals of bird-life have not been well kept by the 

 rocks ; and many kinds of birds must have lived and died of 

 which absolutely nothing is known. 



The best evidence of Oligocene birds has been obtained 

 from strata in France ; and it is clear that a variety of birds 

 disported in the waters of that region. Some were of compo- 

 site character, and were probably on the line of descent to 

 modern grebes and divers (Colymboides}. Others, related 

 to the albatross-like forms of the Eocene, closely resembled 

 the sea-skimming shearwaters of to-day (Puffinus). Solan 

 geese quite of modern type were plunging after prey (Sula). 

 Cormorants vaguely in promise in Cretaceous tunes were 

 now completely evolved (Phalacrocorax) ; and gulls, much 

 resembling living forms, were also on the wing (Larus). 

 Pelicans and big, quaint birds with affinities to gannets and 

 pelicans were fish-hunting in the shallows (Pelacanus, 

 Pelagornis). Ibises and flamingoes of modern genera had 

 now taken the place of their less sharply defined Eocene 

 ancestors (Ibis, Phcenicopterus). But some flamingo-like birds 

 with very mixed affinities were here and there presumably 



