Kryukova N.V. 2018. Vestigial teeth of the Pacific walrus Odobenus rosmarus divergens Illiger, 1815 (Carnivora: Odobenidae) // Russian J. Theriol. Vol.17. No.2: 78–84 [in English].
Natalia V. Kryukova [email@example.com] Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), 17, Verkhnyaya Krasnosel’skaya Street, Moscow, 107140, Russia.
ABSTRACT. Vestigial teeth of the Pacific walrus from the Chukotka Peninsula (Russia) were examined for 94 specimens. The following teeth were studied: the second upper and the third lower incisors, the fourth upper premolar, and the first upper and first lower molars. The upper second incisor is the largest among vestigial teeth and is less likely to be reabsorbed than the others. Growth duration for the majority of vestigial teeth is short (1–2 years). For most of the vestigial teeth, independent of the total number of cement layers and/or age of the walrus, only the enamel and partial upper part of dentine were worn off — without deforming any cementum layers. Generally the weight and width of the upper second incisor and the upper fourth premolar will increase relative to the number of annual cement layers added. For the majority of vestigial teeth examined, the number of cement layers coincided on pairs of teeth the same individual but seldom coincided with the number of cementum layers on other non-vestigial teeth. Because of irregular deposition of cementum layers, vestigial teeth should not be used for age determination of purposes.
KEY WORDS: Pacific walrus, Odobenus rosmarus divergens, persistent deciduous teeth, rudimentary teeth, Pinnipeds, determination of age, morphology of teeth.