ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



93 



l3 p. p2 p3 



C, P2 P3 P4 



Fig. 60. Changes in relative length of the functional cheek teeth of the Pacific walrus 

 with increasing age. Length of each tooth is expressed as percentage of the total 

 combined length of all cheek teeth in one side of the mouth. Bars show range and mean 

 ± 1 S.E. (open) and ± 1 S.D. (solid) of measurements from 11 animals 1 to 6 years old 

 (connected by solid lines) and from 7 that were 14 to 26 years old (connected by dashed 

 lines). 



vertically in either the upper or lower toothrows but are mostly inclined antero- 

 laterally some 10 to 20°; the upper teeth are more inclined than the lower (Figs. 

 61, 62). Many of the teeth also tend to be slightly arched (the lower more than 

 the upper), with the anterior and lateral surfaces of the root concave and the 

 posterior and medial surfaces convex. The lower canine usually is the straightest 

 and most vertical; P3 and P4 are the most curved and obliquely set. 



The occlusion of the cheek teeth with their antagonists resembles that in other 

 mammals, in that the crowns of the upper teeth usually are slightly lateral to 

 those of the lower teeth (Fig. 61, right). The occlusion differs most remarkably in 

 the occlusion of P exclusively with Cj, Pl mainly with P2, mainly with P3, 

 and P3 almost exclusively with P4. Although the lower teeth usually are situated 

 somewhat posterior to their antagonists, the trend is toward end-to-end occlusion 

 (Cobb 1933). In 30 specimens that I examined, 10 had nearly perfect end-to-end 

 occlusion, 8 had end-to-end occlusion with the lower teeth slightly ahead (3) or 

 slightly behind (5) the upper, and 12 had various combinations of end-to-end 



