ECOLOGY AND BIOLOGY OF THE PAGIFIC WALRUS 



97 



Q I .. I . I . I . I I I I I I I I I I 1 I I I I I I 



0 5 10 15 20 25 30 



Age (years) 



Fig. 64. Change in length of the second upper premolar and the lower canine with age 

 in male (dots) and female (circles) Pacific walruses. Each point represents data from one 

 specimen. Visually fitted curves are estimated means for males (solid) and females 

 (dashed) . 



by a distinct ridge about its perimeter (Fig. 66b). This feature, and its 

 remarkably perfect fit with the occlusal surface(s) of its antagonist(s), suggests 

 that this facet is produced entirely by percussion of microlithic particles between 

 the opposing teeth. The possibility that larger, hard objects, such as molluscan 

 shells, are treated there seems remote, for mastication of those would tend to 

 destroy the delimiting ridge and to blend the borders of this facet with those 

 adjacent to it. 



The second facet is the lingual facet which is located on the lingual (medial) 

 surface of the clinical crown of each of the functional cheek teeth. This facet is 

 oblique to the long axis of the tooth and, in adults, may be nearly parallel with 

 the gingival surface (Fig. 66b). In middle-aged and older females, the lingual 

 facet of the upper teeth often is on a level with the gingival surface (Fig. 67). This 

 facet ordinarily is very large on the teeth of females, occupying 20 to 80 % of the 

 surface of the clinical crown; it is smaller on the teeth of males (5 to 60 % of the 



