This study describes the occurrence of dental anomalies in a specimen of Lontra longicaudis from the extreme south of Brazil. The specimen examined (MCNU-1584) underwent radiographic and macroscopic analysis of the dental number, shape and structure. Anomalies were observed in the alveoli of the right PM1 and PM2, which were obstructed by bone tissue and tooth loss was possibly due to trauma or pathogenesis. The presence of a supernumerary tooth, not erupted, inclined and incisiform, was also observed on the midline of the palate. Its position and null functionality suggest that it originated because of the hyper development of the dental lamina.