48 



NORTH AMERICAN FAUNA 68 



cedents are small and nonfunctional ; they are probably shed when 

 the permanent incisors erupt. 



As Hildebrand (1954) has pointed out, the spade-shaped and 

 somewhat protruding permanent lower incisors are used to scoop 

 food organisms from their shells when the sea otter is feeding. In 

 older animals they show wear (fig. 25). 



The sea otter is the only member of the order Carnivora with 

 only two pairs of lower incisors. In this respect, it resembles the 

 pinnipeds, most of which also have only two pairs of lower in- 

 cisors. The walrus has no lower incisors in the adult dentition. 



Canines 



At birth the deciduous canines are erupted. They are shed and 

 replaced following the loss and replacement of the deciduous 

 caniniform incisors at about 5-6 months of age. 



Figure 25. — "Old" adult dentition. No method of determining chronolog-ical 

 age has been found, but animals with severely worn teeth like this were 

 classified as "old." The worn lower incisors and canines and severely 

 eroded postcanines and molars result when hard-shelled organisms are 

 crushed by the teeth. This male, weight 55 lb. (25 kg.), length 1,420 mm., 

 was captured on a beach at Amchitka Island, 14 March 1959. (KWK 

 66-12-10) 



