EOCENE PERIOD 131 



tions {Prozeuglodon), and in some cases the teeth had been 

 reduced in number (Zeuglodon). 



These pioneer, whale-like forms may have been ancestors 

 of the toothed whales (Odontoceti), represented to-day by 

 sperm-whales, dolphins, and porpoises. They probably pos- 

 sessed, like the incipient sea-cows, usable hind-limbs. Re- 

 mains indeed of such appendages, although not externally 

 visible, are found in living whales. 



Before the close of the Period these adventurous mammals 

 had greatly extended their range, having found their way 

 to North and South American seas. Here some of them 

 attained gigantic proportions. 



Whether persecution by some carnivorous reptiles, a 

 gradually developed taste for the salt-water population, or 

 geographical changes impelled the first adventurers to put 

 out to sea cannot be determined. The experiment at any 

 rate was attended with success ; and whales — no less than 

 sea-cows — have never since shown a disposition to quit the 

 adopted element. 



Eocene bird-life, as may be supposed, has its surprises birds 

 as well as mammaldom : and it can only be very imperfectly 

 linked with the bird-life of the preceding Period. 



Toothed birds had become extinct at the close of the 

 Cretaceous, and another affinity with reptiles had been 

 completely lost. There were, however, some gannet-like 

 birds in early Eocene times with what may be called false 

 teeth, for their beaks were notched and serrated like the 

 edge of a saw (Odontopteryx). 



Forms heralding the Albatross were now in being (Argil- 

 lornis), and geese-like birds as large as ostriches (Gastornis). 

 Rails, more or less foreshadowed in Cretaceous times, seem 

 now to have been established (Gypsornis) ; and some related 

 forms — apparently primitive cranes — were wandering about 

 the swamps (Palceogrus). Flamingoes and storks, fore- 

 shadowed in a composite ancestry in the last Period, had 

 now, so to speak, parted company (Agnopterus, Propelargus) : 

 and birds derived from the same stock, and resembling ibises, 

 were also on the scene {Ibidopsis). Some forms more or less 

 nearly related were herons of primitive description (Prohe- 



