ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 81 



Fig. 52. Fully developed secondary teeth from a 4-year-old male Pacific walrus. 

 (Photo by F. H. Fay) 



whereas the laminae of the other secondary teeth had only begun to 

 differentiate. In fetuses taken 4 months later, the tusks (still within the alveolus) 

 were up to 15 mm long, in contrast to the 1- to 3-mm crowns of the other 

 secondary teeth. In fetuses and calves taken during the perinatal months, the 

 tusks were about four times longer than any of the other teeth. 



The peak of development of the secondary dentition, in terms of maximal 

 numbers of calcified teeth, seems to occur about the time of birth or somewhat 

 earlier. Partial resorption of Ij, and I2 often was detected at that time. 

 Resorption of the vestigial secondary teeth evidently ceases during the first year 

 after birth, and any subsequent losses of teeth are due to abrasion or shedding. 

 Occasional losses of the larger, functional teeth also were recognized, and these 

 seemed to be mostly due to periodontal disease or trauma. The postcanine teeth 

 of old animals sometimes were shed when they became reduced to mere vestiges 

 by continual abrasion. Two very old females had no teeth other than Cl. 



All of the secondary teeth of the walrus have simple (haplodont) crowns and 

 single roots (Fig. 52). The roots of the postcanines sometimes are longitudinally 

 grooved, reminiscent of their former, double-rooted condition, as in the otariids. 

 In general, they are longer and more robust than the primary teeth; only the 

 rudimentary incisors may be no larger than their predecessors. The secondary 

 incisors, other than P, sometimes remain unerupted for several years, but they 

 usually are shed or resorbed within 2 or 3 years after birth. When gingivally 

 erupted, they do not occlude with any antagonists. 



The smallest of the secondary upper postcanines was P4. This was one of the 

 last to develop in the embryonic dentition and often was no larger than the first 



