ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



71 



My opinions on the function of the vibrissae in feeding were derived mainly 

 from observation of free-living and newly captured calves in the Bering Sea, and 

 from observation of eight captive walruses in the New York Aquarium, 

 Marineland of the Pacific, and Sea World-San Diego. Although the behavior of 

 walruses reared in captivity is not necessarily comparable to that of free-living 

 animals, it is at least indicative of the extent of their capabilities. 



I found the rostrum and its vibrissae extremely mobile. Each vibrissa can be 

 moved up, down, and laterally, and can be rotated through at least 100° of arc, 

 such that the tips can be turned upward and inward, toward the center of the 

 snout, as well as downward and outward. During feeding or in exploration of 

 unfamiliar objects, the pad and mustache were extremely active and were 

 capable of directing selected objects toward the mouth while pushing others 

 away. In my opinion, the mystacial pads of these captive walruses were at least 

 as effective as two hands in sorting, selecting, and manipulating materials, and 

 they performed those functions in a very rapid and efficient manner. I saw no 

 signs of the mustache being used either as a filter or as a "broom" (in the 

 mechanical sense), or as a battery of "claws" for tearing apart flesh. In both the 

 free-living and the captive calves, as well as in the subadults and adults in the 

 three aquaria, the entire mustache often was used more as a tactile "broom" for 

 exploring surfaces of other animals, rocks, ice, and unfamiliar objects than as a 

 mechanical device for sweeping. The head often was lowered and raised 

 repeatedly, with the vibrissae in contact with the explored object, and the 

 whiskers were in motion only during the raising of the head. I assume that this 

 was the kind of action interpreted earlier as having a sweeping function. 



The most extreme abrasion of the vibrissae along the upper edge of the snout 

 correlates well with the greater protective cornification of the skin there than 

 elsewhere on the face. Also the angle of incidence and direction of movement of 

 the hard particles that abrade the vibrissae correlate well with those in the 

 abrasion of the tusks, as will be shown in the section on dentition. These 

 relations, plus the powerful levating musculature of the head and neck, all point 

 to frequent and strenuous use of the snout as a digging or "rooting" organ. 



Dentition 



The dentition of the walrus was studied by several leading anatomists and 

 naturalists of the 18th and 19th centuries, with particular concern for dental 

 homologies and descriptive dental formulae. In a review of their work, Allen 

 (1880) noted a certain lack of accord on the dental formulae but observed that 

 the problem of homologies of the upper and lower incisors and of the lower 

 canines had been solved. The dental formulae were revised further in the present 

 century by Cobb (1933), based in part on reinterp relation of the earlier work 

 and in part on his own observations. Cobb also described in detail the dental 

 morphology and structural peculiarities of the skull which he considered to be 

 associated with the method of feeding and the development of the tusks. Cobb's 

 report has been the accepted standard reference on the dentition of modern 

 walruses for 50 years. 



