Dark Is Be j ore the Dawn 355 



the head could be freely turned about. Most important of all, their 

 teeth were only thirty-six in number and were also differentiated, 

 Hke our own and those of most other land animals, into groups — 

 simple front teeth, pointed eyeteeth, or canines, and complex grind- 

 ing teeth, or molars. The skull and skeleton also retained many other 

 nonwhale and typically terrestrial mammalian features. The bones 

 of the upper arm, for instance, were proportionately much longer 

 than in other whales. Zeuglodonts, in fact, fit quite well into an evo- 

 lutionary series from land animal to marine whale, though we know 

 nothing of their soft parts, and so cannot tell exactly at what evolu- 

 tionary point they may be placed. Their real significance is the ar- 

 rangement and number of their teeth, especially when considered in 

 conjunction with those of the Squalodonts which are, in some re- 

 spects, intermediate between them and the modern toothed whales. 



The next step backward takes us into the Oligocene Period, one 

 of some sixteen milHon years' duration, between thirty-five million 

 and nineteen million b.c. In the rocks laid down under seas of this 

 period we find only extinct forms — Cetotheres, Squalodonts, and 

 Zeuglodonts. The rights, rorquals, grays, and porpoises have not yet 

 been evolved, and we have no evidence of sperms, ziphioids, dol- 

 phins, or platanistids. There is very good reason to suppose that 

 they or their immediate ancestors were around somewhere, but they 

 either did not get themselves fossilized, or did so in strata that we 

 have not yet unearthed. The gray whale of today must be very like 

 the first rorquals, and the two groups may merge ancestrally some- 

 where between the late Oligocene and the early Miocene. The ziphi- 

 oids of today appear to be even more primitive, and they may have 

 had a common ancestry with Acrodelphids. The sperms are a very 

 ancient and most distinct family that must have had a long evolution 

 before their appearance in the Miocene. The little platanistids, which 

 today live in fresh water, appear suddenly in the lower Miocene. 

 Nothing is known of their ancestry prior to this time, but they are 

 even more likely to have been around, and for longer than all the 

 other present-day groups. From this point backward our steps can 

 be only few and rapid. 



Before the Oligocene comes a twenty-million-year period called 

 the Eocene. Whales from this time are all either very primitive 

 Squalodonts or Zeuglodonts. The former make their first appearance 



