UC Davis UC Davis Previously Published Works Title Dental and Temporomandibular Joint Pathology of the Walrus (Odobenus rosmarus). Permalink https://escholarship.org/uc/item/05z8k86z Journal Journal of comparative pathology, 155(2-3) ISSN 0021-9975 Authors Winer, JN Arzi, B Leale, DM et al. Publication Date 2016-08-13 DOI 10.1016/j.jcpa.2016.07.005 Peer reviewed eScholarship.org Powered by the California Digital Library University of California J. Comp. Path. 2016, Vol. -,1e12 Available online at www.sciencedirect.com ScienceDirect www.elsevier.com/locate/jcpa DISEASE IN WILDLIFE OR EXOTIC SPECIES Dental and Temporomandibular Joint Pathology of the Walrus (Odobenus rosmarus) J. N. Winer*, B. Arzi†, D. M. Leale†,P.H.Kass‡ and F. J. M. Verstraete† *William R. Pritchard Veterinary Medical Teaching Hospital, † Department of Surgical and Radiological Sciences and ‡ Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA, USA Summary Maxillae and/or mandibles from 76 walruses (Odobenus rosmarus) were examined macroscopically according to predefined criteria. The museum specimens were acquired between 1932 and 2014. Forty-five specimens (59.2%) were from male animals, 29 (38.2%) from female animals and two (2.6%) from animals of unknown sex, with 58 adults (76.3%) and 18 young adults (23.7%) included in this study. The number of teeth available for examination was 830 (33.6%); 18.5% of teeth were absent artefactually, 3.3% were deemed to be absent due to acquired tooth loss and 44.5% were absent congenitally. The theoretical complete dental formula was confirmed to be I 3/3, C 1/1, P 4/3, M 2/2, while the most probable dental formula is I 1/0, C 1/1, P 3/3, M 0/0; none of the specimens in this study possessed a full complement of theoretically possible teeth. The majority of teeth were normal in morphology; only five teeth (0.6% of available teeth) were malformed. Only one tooth had an aberrant number of roots and only one supernumerary tooth was encountered. No persistent deciduous teeth were found in any of the young adult or adult specimens, nor were any specimens affected by enamel hy- poplasia. The majority of teeth (85.5%) displayed attrition/abrasion. Of the adult and young adult specimens, 90.8% showed some degree of attrition/abrasion on at least one tooth. Tooth fractures were noted in eight wal- ruses, affecting 10.5% of specimens and 1.3% of the total number of teeth, nearly three-quarters of which were maxillary canine teeth (tusks). Three specimens (3.9%), all adult males, displayed overt periapical disease. The majority (99.2%) of dental alveoli did not have bony changes indicative of periodontitis, with only five specimens (6.6%) affected by periodontitis. Lesions consistent with temporomandibular joint osteoarthritis (TMJ-OA) were found in 46 specimens (60.5%) and TMJ-OA was significantly more common in adults than young adults and males than females. Although the clinical significance of dental and TMJ pathology in the walrus remains unknown, the occurrence and severity of these lesions may play an important role in the morbidity and mortality of this species. Ó 2016 Elsevier Ltd. All rights reserved. Keywords: dental formula; dental pathology; temporomandibular joint pathology; walrus Introduction Pole, in the Arctic Ocean and subarctic seas, in a discontinuous range. They are a social species, living Odobenus rosmarus The walrus ( ) is the sole extant spe- in groups occupying shallow waters, spending large Odobenus cies in the family Odobenidae, genus , with amounts of time on sea ice. Walruses live up to 30 O. rosmarus three subspecies: (the Atlantic walrus), years in the wild (Fay, 1955). The Pacific walrus dem- O. rosmarus divergens O. rosma- (the Pacific walrus) and onstrates pronounced sexual dimorphism (Fay, rus laptevi (inhabiting the Laptev Sea of the Arctic 1982). Adult males have a mean body length of Ocean). Walruses are distributed across the North 320 cm and an average body weight of 1,200 kg, while adult females have a mean body length of 272 cm and Correspondence to: F. J. M. Verstraete (e-mail: [email protected]). 0021-9975/$ - see front matter Ó 2016 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcpa.2016.07.005 Please cite this article in press as: Winer JN, et al., Dental and Temporomandibular Joint Pathology of the Walrus (Odobenus rosmarus), Journal of Comparative Pathology (2016), http://dx.doi.org/10.1016/j.jcpa.2016.07.005 2 J.N. Winer et al. an average body weight of 800 kg (Fay, 1982). tusks up to 80 cm in length (Fay, 1982). Apart from Among pinnipeds, walruses are only exceeded in the tusks, walrus dentition is made up of single- size by the elephant seals (Mirounga leonina and Mir- rooted peg-like teeth, which measure 2.5e5.5 cm in ounga angustirostris). length and 1.0e2.5 cm in diameter when fully formed The majority of walrus prey is located on the ocean (Fay, 1982). The incisor teeth (except for the maxil- floor, on or just beneath the surface of the sediment, at lary third incisor tooth) and molar teeth are vestigial a depth of less than 100 m (Fay, 1982; Fay and Burns, and typically resorb prior to adulthood (Fay, 1982). 1988). The walrus locates its prey with its vibrissae Walrus occlusion is consistent with other carnivores and then uncovers it with its snout (Fay, 1982). Anal- in that it is anisognathous, the mandibles being nar- ysis of fresh stomach contents revealed that walruses rower than the maxillae. consume a diverse diet, comprised of 100 taxa from Their remote location and fragmented distribution 11 phyla (Sheffield et al., 2001; Sheffield and make quantifying the total walrus population chal- Grebmeier, 2009). Walruses rarely ingest large non- lenging (Speckman et al., 2011). The Pacific walrus benthic organisms such as fish, birds and seals population was severely depleted in the late 19th cen- (Freuchen, 1935; Vibe, 1950; Fay, 1982; Lowry and tury and in the mid-20th century by commercial Fay, 1984; Gjertz, 1990; Donaldson et al., 1995), but hunting, but rebounded when harvests were reduced typically walruses utilize suction to remove (Fay, 1982). More recently, predation, intraspecific molluscan prey from their shells (Vibe, 1950; Fay, trauma and microbial infections were reported as 1982). The soft bodies are then swallowed whole, principal causes of mortality (Fay, 1982). With the with no indication of mastication (Fay, 1982). ever-increasing threat of global climate change, loss In order to counteract the buoyancy of its immense of sea ice habitat is again threatening the walrus pop- blubber and better swim to the benthic floor to forage, ulation (Jay et al., 2011). Dental and temporoman- the walrus skeleton and skull, in particular, are pa- dibular joint (TMJ) lesions, which are common in chyostotic. This non-pathological increase in skeletal certain wildlife species, may be important contribu- mass and density is considered to play the functional tors to morbidity and mortality (Verstraete et al., role of ballast for buoyancy control (Ricqles and 1996a,b). Buffrenil, 2001; Houssaye, 2009). A series of papers has been published on dental and Walrus dentition is variable, and the dental for- TMJ pathology of marine mammal species: the mula is represented inconsistently throughout the northern elephant seal (M. angustirostris)(Abbott literature (Kryukova, 2012). Recently it has been re- and Verstraete, 2005), the southern sea otter (Enhydra ported as I 1/0, C 1/1, PC (postcanines) 3/3 (Jefferson lutris nereis)(Arzi et al., 2013a; Winer et al., 2013), the et al., 2008) and also as I 1-2/0, C 1/1, PC 3-5/3-4 California sea lion (Zalophus californianus)(Sinai et al., (Hillson, 2005). The term ‘postcanine’ is occasionally 2014; Arzi et al., 2015), the northern fur seal used in marine mammalogy to denote the premolar (Callorhinus ursinus)(Aalderink et al., 2015a) and the and molar teeth. Fay (1982) amalgamated the results eastern Pacific harbour seal (Phoca vitulina richardii) of previous studies and supplemented that data with (Aalderink et al., 2015b). In general, museum collec- his findings on the Pacific walrus after having exam- tions of skulls, such as those making up the aforemen- ined 136 maxillae and 129 mandibles. He concluded tioned studies and this study, are obtained from that walruses may have between 18 and 38 teeth, rep- strandings, carcass recovery and donations by reha- resenting the adult dental formula as follows: I (1)- bilitation centres. Specific to Alaska, museum speci- (2)-3/(1)-(2)-(3), C 1/1, P 1-2-3-(4)/2-3-4, M (1)- mens are additionally sourced from permitted (2)/(1)-(2). The teeth listed in parentheses were pre- hunting for subsistence purposes and wildlife deaths sent in <50% of his adult specimens (i.e. the maxil- as a result of ‘Defence of Life and Property’ laws. lary third incisor tooth is present consistently, while Pathological conditions are likely overrepresented in the mandibular first to third incisor teeth are present stranded animals as compared with the general pop- in <50% of adult specimens). Thus, the walrus is the ulation (Cowan, 2002); high numbers of stranded an- pinniped species with the greatest number of potential imals may be considered sentinels of emerging teeth, but the least number occurring with greater diseases (Gulland, 1999). The number of walrus than 50% probability (Fay, 1982)(Fig. 1). skulls in museum collections is low, as the tusks are The most striking dental feature of the walrus is its highly valued by native people, who are allowed to maxillary canine teeth, referred to as ‘tusks’ because harvest them.