The method of age determination of the Pacific walrus (Odobenus rosmarus divergens) using the layered structure of functional teeth

The functional teeth of Pacific walruses that died or were harvested in the Retkyn Spit, Enmelen village, Kolyuchin Island, Vankarem Cape, Enurmino village, and Chegitun River region in 2005, 2007–2008, and 2010–2011 were examined. The definite structure was investigated in animals of their first year of life. The presence of a milk layer in the tooth dentine can be considered as a mark that all the cement layers have been preserved, and the age determination of an individual is precise. The annual increment of dentine significantly changed with age in different parts of the tooth (buccal, lingual, and central), and the annual growth of dentine decreased every year. The growth rate of the upper jaw teeth was significantly higher, and the duration of their growth was much longer than that in the lower jaw teeth. The wearing of dentine and cement layers was unequal in different parts of tooth. Several recommendations for choosing a tooth for the determination of the walrus’s age and for the estimation of age using the layered tooth structure are given.