102 Thomas D. Beaver, George A. Feldhamer, Joseph A. Chapman 



— reduced dental complement due to teeth that failed to develop; and 

 8) irregular placement — teeth in positions other than the normal pat- 

 tern. Skulls were X-rayed to provide confirmation of suspected agenesis 

 or supernumeration. 



RESULTS AND DISCUSSION 



A total of 137 skulls (67.8%) exhibited no cranial abnormalities or 

 deviation from the normal dental pattern of 3/3, 1/1,4/3, 1/2 = 36 in L. 

 canadensis. Anomalies were found in 65 skulls (32.2%). This is similar 

 to the results of Colyer (1936) who noted "marked irregularities" in 75 

 of 161 (46.6%) skulls of Lutra sp. — a greater percentage of occurrence 

 of anomalies than in any other genus of Mustelidae he examined. 



Cranial anomalies. — Cranial anomalies occurred in only 2 (1.0%) 

 of the skulls examined. Plagiocephaly was found in an adult female over 

 3 years of age, and there was a small hole in the frontal bone (Fig. 1). 

 Mowbray et al. (1979) indicated that 1 1% of the 296 river otter carcasses 

 that they examined from this study area showed evidence of gunshot 

 wounds, although few animals (1.7%) were judged to have died from 

 such wounds. Dougherty and Hall (1955) and van Soest et al. (1972) 

 noted that characteristics similar to those seen in Figure 1 may result 

 from metastrongylid nematode (Skrjabingylus sp.) involvement. Thus, 

 the plagiocephaly may have resulted from an extrinsic agent, either a 

 nonlethal gunshot wound or a parasite, rather than genetic factors. 

 Heterotopic bones occurred on the premaxilla of an adult male over 3 

 years of age (Fig. 2); there were no indications of previous injury. 

 Whether this condition was genetic in origin or resulted from previous 

 trauma could not be determined. No instances were found of bregmatic 

 bones. 



Dental anomalies. — Dental anomalies were much more prevalent 

 than cranial anomalies. With the exception of caries, an example of 

 each dental anomaly was represented in the sample. The lack of caries 

 in wild animals is consistent with previous studies. Hall (1940) found 

 caries in only 8 of 3,761 specimens (0.2%) of North American carniv- 

 ores, and all cases occurred within the Ursidae. Colyer (1936) reported 

 only 4 cases of caries in 7,635 specimens (0.05%) of North American 

 carnivores. The reason for lack of caries in the river otter, as well as 

 most other carnivores, is unknown, although it may be associated with 

 absence of carbohydrates in the diet. 



Irregular tooth placement was noted in two individuals: a juvenile 

 female had teeth that were abnormally far apart (Fig. 3), and in an adult 

 female they were exceedingly close together (Fig. 4). 



Alveolar thinning (Fig. 5) was the most common anomaly, occurr 

 ing in 47 skulls (23.3%). Of these, 39 (82.9%) involved the last upper 



