Vestigial teeth of the Pacific walrus Odobenus rosmarus divergens Illiger, 1815 (Carnivora: Odobenidae)

Vestigial teeth of the Pacific walrus Odobenus rosmarus divergens Illiger, 1815 (Carnivora: Odobenidae)

Kryukova N.V.

P. 78-84

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.DOI: 10.15298/rusjtheriol.17.2.03

Literature
  • Allen J.A. 1880. History of North American pinnipeds. A monograph of the walruses, sea lions, sea bears and seals of North America. Washington: Government printing office. 773 p.
  • Cobb W.M. 1933. The dentition of the walrus (Odobenus obesus) // Proceedings of the Zoological Society of London. Vol.103. No.3. P.645–668.
  • Drehmer C.J., Sanfelice D. & Loch C. 2015. Dental anomalies in pinnipeds (Carnivora: Otariidae and Phocidae): occurrence and evolutionary implications // Zoomorphology. Vol.134. No.2. P.325–338.
  • Fay F.H. 1982. Ecology and biology of the pacific walrus, Odobenus rosmarus divergens, Illiger // North American Fauna. Vol.74. Washington, D.C.: US Department of the Interior, Fish and Wildlife Service. 279 p.
  • Klevezal G.A. 1988. [Recording structures of mammals in zoological studies]. Moscow: Nauka. 283 p. [In Russian]
  • Krylov V.I. 1965. [Determination of age, growth rate and age structure of the Pacific walrus population] // Pavlovskii E.N., Zenkovich B.A., Kleinenberg S.E., Chapskii K.K. (eds.). Morskie mlekopitayushchie. Moscow: Nauka. P.201–211 [in Russian].
  • Kryukova N.V. 2012. Dentition in Pacific walrus (Odobenus rosmarus divergens) calves of the year // Biology Bulletin. Vol.39. No.7. P.618–626.
  • Kryukova N.V. 2014. The method of age determination of the Pacific walrus (Odobenus rosmarus divergens) using the layered structure of functional teeth // Biology Bulletin. Vol.41. No.8. P.681–689.
  • Kryukova N.V. 2017a. Age-related changes in functional teeth in the Pacific walrus (Odobenus rosmarus divergens) // Biology Bulletin. Vol.44. No.7. P.820–825.
  • Kryukova N.V. 2017b. Caries in teeth of the Pacific walrus // Abstract book. 22nd Biennial conference on the Biology of Marine Mammals (Halifax, Nova Scotia, Canada, October 22–27). Halifax. P.217.
  • Kuzin A.E. 1999. [Northern fur seal]. Moscow: Marine Mammal Council. 395 p. [In Russian]
  • Luckett W.P. 1993. An ontogenetic assessment of dental homologies in Therian Mammals // Szalay F.S. Novacek M.J., McKenna M.C. (eds.). Mammal Phylogeny. New York: Springer Science+Business Media. P.182–203.
  • Mansfield A.W. 1958. The biology of the Atlantic walrus, Odobenus rosmarus rosmarus (Linnaeus) in the eastern Canadian Arctic // Fisheries Research Board Canada Manuscript Report Series (Biology). No.653. 146 p.
  • van der Merwe M. 1997. Vestigial teeth in the genus Scotoecus (Mammalia: Chiroptera): adapted dental formulae for vespertilionids with vestigial teeth // South African Journal of Zoology. Vol.32. No.3. P.76–81.
  • Miles A.E.W. & Grigson C. 1990. Colyer’s variations and diseases of the teeth of animals. Revised edition. Cambridge: Cambridge University Press. 676 pp.
  • Moss-Salentijn L. 1978. Vestigial teeth in the rabbit, rat and mouse; their relationship to the problem of lacteal dentitions // Butler P.M., Joysey K.A. (eds.). Development, Function and Evolution of Teeth. London: Academic Press. P.13–29.
  • Nweeia M.T., Eichmiller F.C., Hauschka P.V., Tyler E., Mead J. G., Potter C.W., Angnatsiak D.P., Richard P.R., Orr J.R. & Black S.R. 2012. Vestigial tooth anatomy and tusk nomenclature for Monodon monoceros // The Anatomical Record Vol.295. No.6. P.1006–1016.