THE SKULL 



Unless some complication be introduced there is fundamentally little 

 need for a rostrum of more mass than the mandible, and this is the case 

 in Platanista. Unless there be some antagonistic influence in operation 

 the tendency should be for the cetacean rostrum to diminish in width 

 and perhaps increase in length to a reasonable extent, thus acting as a 

 cut-water. This it has done in some instances, but whether for this 

 reason or because of food habits is of course unknown. In Platanista 

 the two sides of the maxillary dental arch are so close together that they 

 partly blend. The extinct Zarhachis had a rostrum five times as long as 

 the cranium proper, and in Eurhinodelphh bossi the rostrum constituted 

 nine-elevenths of the total skull length (Kellogg, 1928), although in 

 some specimens of the last the mandible was considerably shorter. Theo- 

 retically a long, tweezer-like beak would be best for capturing small 

 active fish which dart about in schools, but it is difficult to see how a 

 beak of such length as that of Eurhinodelphis could be effectively used 

 in conjunction with the limitations of a short cetacean neck; and it 

 doubtless constituted an overspecialization. Because there have surely 

 been many complications, however, we find rostra of all shapes, down to 

 exceedingly short, broad ones such as in Globiocephala in which the 

 stubby mandible, overhung by a rostral frontal bulge, appears ideal for 

 scooping up relatively inactive, bottom-living food; and yet these whales 

 are said to feed on cephalopods. 



The rostrum of a porpoise with moderate beak, such as Tursiops, com- 

 posed of the maxillaries and premaxillaries, is relatively thin in vertical 

 dimension, and certainly not as strong as the average land mammal with 

 equal rostral length would require. The killer whales, with their carniv- 

 orous habits, need a stronger rostrum and have it. But the rostrum of 

 Physeter is certainly not as massive as one would expect to see as the 

 support of its huge frontal fatty equipment, and the rostrum of the 

 balaenid whales appears very fragile as a scaffold for their remarkable 

 baleen armature. Mechanically the attachment of the Mysticeti rostrum 

 to the rest of the skull is very weak, for the principal sutures are largely 

 in one plane where they could all be acted upon by a single oblique force. 

 But it has been entirely adequate for the needs of the animal and that is 

 all that is requisite. On the other hand, the attachment of the base of 

 the odontocete rostrum to the cranium is mechanically of exceeding effi- 

 ciency. It is broadly distributed ijn laminated, squamous sutures in a 

 manner that is stronger than could be accomplished by dentate sutures 

 of the usual sort. And this is not surprising, for the stress which the 

 cetacean rostrum must undergo is applied almost exclusively in a pos- 



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