FEEDING 



Figure 148. Skull of Sqiialodon bariense from the middle Aiiocene {France ; about 

 /J million years old). {Kellogg, igsS.) 



Fragilariopsis antarctica. Coarse and large diatoms are apparently rejected 

 by means of a complicated system of hair on the legs which acts as a 

 primary filter (Fig. 146). The remaining material, i.e. the small diatoms, 

 passes through a much finer filter and is then swept into the mouth by 

 movements of the legs. 



Mysticetes are the only whales which feed on plankton, other Cetaceans 

 having teeth instead of a strainer. Their teeth are, however, quite different 

 from those of terrestrial mammals. The supposed ancestors of our modern 

 whales (see Chapter 2) probably had three incisors, one canine, four 

 premolars and three molars in either jaw, and so had the oldest represen- 

 tatives of the Archaeocetes, e.g. Protocetus. Younger forms such as Basilo- 

 saurus and Doriidon had molars with a serrated edge (Fig. 147). F. C. Fraser 

 has shown that these molars have a very close resemblance to those of 

 the recent Crabeater Seal {Lobodon carcinophagus) . This animal mainly feeds 

 on fairly small crustaceans and these may also have been the main food 

 of the younger Archaeocetes. Serrated teeth are also found in the oldest 

 known Odontocetes, the Squalodonts which, moreover, had a marked 

 lengthening of the jaws (Fig. 148). The ideal set of teeth for fish eaters is, 

 in fact, a long row of even and conical teeth. 



In all modern Odontocetes the individual teeth are, in fact, so similar 

 that it is difficult to distinguish them. The posterior part of the row of 



Figure i4g. The 6th, 22nd, 38th, jyth, 4.0th and 43rd 

 tooth-buds from the left lower jaw of a 40-inch Fin Whale 



foetus, showing that the rear buds have three points. 

 {Van Dissel-Scherft and Vervoort, 1954.) 



