34. The Dentition of the Walrus, Odobenus obesus

1 The dental peculiarities of the walrus, Odobenus obesus, may be ascribed in their entirety to the structural modifications induced by the huge size of the canine tusks and to the diet which the animal has adopted. 2 The dental succession is best represented by the formulæ: Deciduous i. 3/3, c. 1/1, m. 3/3 = 28; Successional I. 2/0, C. 1/1, P. 4/3, M. 1/1 = 26; Functional I. 1/0, C. 1/1, P. 3/3 = 18. The last of these is well known. The first differs from previous interpretations in recognizing but three milk‐molars, and the second is devised to acknowledge definitely the existence of a successional upper second incisor and fourth premolar and to designate as true molars the upper and lower posterior rudimentary teeth. 3 The enlargement of the upper canines has caused the loss of the medial incisors, the alignment of the outer upper incisor and lower canine with the cheek‐teeth, and an antero‐lateral shift in the angle of implantation of the upper teeth. 4 The diet, composed chiefly of hard‐shelled molluscs, has required a concentration of force in the anterior portion of the mouth. This has been accomplished by the production of massive jaw‐bones and heavy solid dental columns. 5 The necessity for an adequate dental armament at an early age has been met (a) by a long period of suckling, while the face and teeth were growing; (b) by the nearly simultaneous eruption of the entire dental battery; and (c) by the expanding cones of the growing roots, which made it possible for dental equipment to keep pace with facial development without additional teeth, a mechanism not noted in any other mammal. 6 The details of the processes of structural modification, growth, wear, and senescence related to the dentition have been recited according to the evidence available. 7 By the application of the principles set forth in this discussion miscellaneous specimens of teeth may be identified with reasonable accuracy.