72 WHALES 



had teeth, albeit very simple ones, is not in itself sufficient evidence for 

 excluding the animal from the list of possible ancestors, for we have clear 

 indications that the distant forefathers of the Mysticetes were in fact 

 toothed animals. We do not know with any certainty how long ago these 

 animals lived, though it must have been well over 27 million years ago, 

 since their oldest-known Middle Oligocene representatives had lost all 

 traces of teeth - at least the known fossils of adults had. This qualification 

 is important, for even modern Mysticetes cannot be said to be entirely 

 devoid of teeth, which still occur in their foetuses. 



This has been known for the last 150 years, for foetal teeth were first 

 discovered in the lower jaw of a Greenland Whale by Geoffroy St. Hilaire 

 in 1807. Such tooth buds can also be found on the deck of every modern 

 factory ship whenever the foetus of a cow in calf is removed. If an incision 

 is made into the soft mucous membrane of the upper or lower jaw of a Fin 

 Whale foetus aged 4-8 months (ca. 4 feet 3 inches - ca. 10 feet long) a row 

 of conical tooth buds will appear (Fig. 35). In the upper jaw, these tooth 

 buds lie slightly sunken within a white, smooth and glistening ridge from 

 which the young baleen will later develop. The beginnings of the baleen, 

 a row of small cornified transverse ridges, first appears in foetuses when 

 they exceed a length of 10 feet; at this stage the rudimentary teeth of both 

 the lower and upper jaw disappear without a trace. However, their 

 presence during the early stages of foetal development is clear evidence 

 that the Mysticetes are descended from a line of ancestors with teeth in 

 both jaws. 



We have already seen that Archaeocetes could not have been the direct 

 ancestors of the Mysticetes, and it appears that no primitive Odontocetes 

 could have been their ancestors either, for the two difTer too radically in 

 structure and in many other respects. For instance, their oil has a different 

 chemical composition - the oil of Odontocetes being a wax rather than a 

 fat - and secondly, their blood proteins are different, too. Moreover, 

 Dr Kendrew of Cambridge and his colleagues recently showed that there 

 exist differences also in the crystalline form of their myoglobin - the 

 iron-holding pigment in the red muscle. For all these reasons, it is generally 

 assumed that the three great groups of Cetaceans developed quite separ- 

 ately from their terrestrial ancestors, but that the Mysticetes are closer to 

 the Archaeocetes than are the Odontocetes. 



It is even thought that we can form some picture of the ancestors of the 

 different groups, in the sense that both Mysticetes and Archaeocetes can 

 be said to be descended from terrestrial animals with short, and the 

 Odontocetes from animals with long tails. This is inferred from a careful 

 study of very young embryos, those of Mysticetes having the shortest and 

 those of Odontocetes the longest tail in proportion to total body length. 



