Dental and Cranial Anomalies in the River Otter 

 (Carnivora: Mustelidae) 



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



Appalachian Environmental Laboratory, 



Gunter Hall, Frostburg State College Campus, 



Frostburg, Maryland 21532 



ABSTRACT.— Dental or cranial anomalies were noted in 65 (32.2%) 

 of 202 skulls of river otters, Lutra canadensis, collected from the Ches- 

 apeake Bay region of Maryland and Virginia from 1974 to 1979. The 

 most frequent anomaly was alveolar thinning. Anomalies probably did 

 not adversely affect individuals or the population structure. 



INTRODUCTION 



The dentition and cranial structure of many mammalian species 

 have been well studied because of their importance in systematics and 

 taxonomy. Also, the condition of teeth affects nutritional status, which 

 in turn directly affects behavior, reproduction and longevity (Robinson 

 1979). As a result, anomalies have been described for several orders and 

 numerous mammalian species (Choate 1968; Colyer 1936; Hershkovitz 

 1970; LaVelle and Moore 1972; Manville 1963; Pavlinov 1975; Sheppe 

 1964; Shultz 1923). However, relatively few studies have dealt with the 

 Mustelidae (Hall 1940; Heran 1970; Parmalee and Bogan 1977). Here 

 we describe dental and cranial anomalies noted in skulls of river otters, 

 Lutra canadensis, from the Chesapeake Bay region of Maryland and 

 Virginia and assess their probable impact upon individuals and the 

 population. 



MATERIALS AND METHODS 



A total of 202 skulls was collected from trappers in Dorchester 

 County, Maryland, during the trapping seasons of 1974 through 1979. 

 The material was considered a random sample representative of the 

 river otter population as no skull was obtained specifically because it 

 had an anomaly. All skulls were individually numbered and are housed 

 in the museum collection of the Appalachian Environmental Labora- 

 tory (AEL). Each skull was examined for the following: 1) plagio- 

 cephaly — asymmetrical cranial growth due to premature closure of one 

 frontal-parietal suture; 2) bregmatic bones — extra bones derived from 

 accessory ossification in any of the fontanelles; 3) heterotopic bones — 

 small accessory bones; 4) caries — decay of dental tissue; 5) alveolar 

 thinning — exposure of the buccal tooth roots; 6) supernumerary teeth 

 — those in excess of the normal dental pattern; 7) congenital agenesis 



Brimleyana No. 7:101-109. July 1981. 101 



