98 



NORTH AMERICAN FAUNA 74. 



Fig. 65. Examples of thickness of linear 

 increments of cementum on the root 

 apex of the second upper premolar 

 (dots), lower canine (circles), and first 

 lower premolar (triangles) in relation 

 to age of Pacific walruses. Each series 

 of interconnected points is from one 

 specimen; each single point is the latest 

 increment in one specimen. 



' ■ ■ 



0 



10 15 20 

 Age (years) 



25 



30 



crown). Invariably, it is highly polished but typically shows also many fine 

 striations made by abrasive particles. The orientation of those striae, almost 

 without exception, is perpendicular to the principal (vertical) vector of occlusive 

 force but is parallel to the long (horizontal) axis of the tongue. This orientation 

 indicates that the abrasion of the lingual facet takes place mainly as a 

 consequence of longitudinal motion of the tongue, carrying fine, microlithic 

 particles. Vertical striations, such as one might expect to be inscribed by clam 

 shells being crushed in this area, were conspicuously absent in nearly all of the 

 approximately 50 specimens that I examined for this character. 



The third area from which material is deleted from the clinical crown is the 

 labial facet. This facet is present only on the mandibular teeth and is most 

 apparent on Fo. Like the lingual facet, it always is highly polished and slightly 



Table 12. Estiinated rates of linear decrement of dental tissue from the distal 



tip of the lower canine and 



second upper premolar of some 



Pacific walruses. 









Estimated rates 





Specimens 



Decrements 



(mm/yr) 



Tooth 



Sex No. 



Time (yr)'^ Amount (mm)'^ 



Range Mean 





M 3 



22 35 



0.89-2.50 1.59 





F 2 



41 46 



0.88-1.28 1.12 



p2 



M 3 



35 27 



0.64-1.00 0.77 





F 4 



48 33 



0.62-1.00 0.69 



^Sum of total years in which decrements took place. 

 bSum of cumulative total measured amounts of decrement. 



