110 ALLEN: NEW ENGLAND WHALEBONE WHALES. 



THE WHALEBONE WHALES. 



The living Cetacea comprise two well defined groups or suborders, the toothed whales or 

 Odontoceti, and the whalebone whales or Mystacoceti. To the former group belong the Dol- 

 phins (Delphinidae) , the Sperm Whales (Physeteridae), and the Beaked Whales (Ziphiidae). 

 To the latter group belong those that instead of functional teeth have whalebone plates depend- 

 ing from the roof of the mouth. Three families of whalebone whales are currently recognized: 

 the Balaenidae (Right Whales), Balaenopteridae (Finback Whales), and Rhachianectidae (Gray 

 Whale). That the whalebone whales sprang from toothed forms is evidenced by the fact that 

 ; ; vestiges ef the' original teeth are found within the gums of the embryo. Probably both groups 

 are ^of common ancestry, although this must be very remote in time. In many respects the 

 Tvha'lebone whales have become more modified than the toothed whales. Thus they have lost 

 their teeth, developed whalebone or baleen in their stead, have in some genera suffered reduction 

 of the fingers in the skeleton, the sternum and the sternal ribs have nearly disappeared and 

 the true ribs have largely lost their capitular processes. On the other hand they have retained 

 so primitive a feature as a double blowhole, corresponding to the two nostrils, whereas in all 

 living Odontocetes the blowhole is single. They also retain a considerable number of hairs on 

 the head, even in the adult, whereas in the toothed whales, the few vestiges of hairs are early 

 lost. 



Four genera of baleen whales are now recognized as occurring in the North Atlantic: 

 Balaena, Eubalaena, Balaenoptera, and Megaptera. The first-named includes only the single 

 species, Balaena mysticetus, the Bowhead or Arctic Whale. It is characterized by its enormous 

 head which comprises a third of the total length, and its greatly arched upper jaw with its 

 narrow plates of whalebone reaching fifteen feet in length. This species is typically an ice 

 whale, and follows the edge of the pack-ice in the circumpolar waters of the Arctic Ocean. In 

 former times it was common as far south as Newfoundland and the Gulf of St. Lawrence but 

 is not certainly known from New England (but see pp. 134, 135 for possible records). 



Closely related to this is Eubalaena, the Right Whale, characterized by its much shorter 

 head in proportion, and its less arched skull. Both genera have a number of unspecialized 

 characters as compared with the Finbacks (Balaenoptera) including the lack of a dorsal fin, 

 absence of throat folds, the presence of the typical five fingers in the hand, the greater number 

 of ribs that retain a double articulation with the vertebrae, and the relatively considerable 

 size of the vestigial femur or thigh bone. On the other hand the partial fusion of the neck 

 vertebrae, the extraordinary narrowing of the rostral portion of the cranium, and the great 

 convex curvature of this part of the skull correlated with the long whalebone plates are features 

 of high specialization over the conditions seen in other whalebone whales. To these characters 



