CHAPTER XVII 



THE WHALES AND PORPOISES 



Whalebone Whales and toothed Whales — Evolution of the den- 

 tition in the toothed Whales — Ancestry of the Whales — 

 Dentition of the Porpoise. 



Of the Cetacea there are two suborders, one the Mystacoceti 

 or whalebone Whales, very highly specialized and possessing 

 instead of teeth large masses of whalebone hanging from the 

 roof of the month ; the other the Odontoceti or toothed Whales 

 having simple peg-like teeth sometimes in great number. 

 Whereas the former group feeds upon small shrimp-like crusta- 

 ceans and swimming molluscs the latter is carnivorous in habit. 

 With the Mystacoceti we shall not deal in this volume although 

 minute vestigial two- and three-rooted teeth have been de- 

 scribed as existing in whalebone Whales prior to birth, but 

 shall devote our attention solely to the toothed Whales with 

 which are associated the Porpoises and Dolphins. 



These animals though possessing teeth are in many respects 

 even more specialized and aberrant than the Mystacoceti and 

 it is probable that the two are parallel groups possessing a 

 common ancestor but diverging from each other during their 

 phylogenetic history. The simple peg-like tooth armament or 

 to speak in scientific terms, the haplodont, homodont dentition 

 of the Odontoceti is not primitive as might at first appear 

 but is derived secondarily from the more typical tritubercular 

 tuberculo-sectorial form. This secondary simplification is an 

 adaptation to aquatic carnivorous feeding and is seen in a less 

 advanced stage in the Sea-lions and Seals. In the toothed 

 Whales as well as in the Pinnipedia there is very great varia- 



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