| Summary: | ABSTRACT Dental anomalies have been investigated and reported for most orders of mammals, including marsupials. Previous works in Didelphis albiventris Lund, 1840 only described one kind of malformation or just a few observations from some collections, thus the type and presence of anomalies for this species was underestimated. The aim of this contribution is to describe and analyze several dental anomalies found in specimens of Didelphis albiventris from Argentina, Uruguay and Brazil. Dental anomalies were classified in three categories: supernumerary or missing teeth, morphological anomalies in size and shape, and teeth in unusual positions. We found 32 individuals of D. albiventris with anomalies out of 393 analyzed specimens (8.14%), some specimens with more than one anomaly. A similar proportion of specimens from Argentina and Uruguay presented anomalies, while in specimens from Brazil anomalies were less common. Anomalies were more commonly found in the upper toothrow and in molars, being supernumerary teeth and molars with unusual crown-shape the most common ones. The percentage of specimens with anomalies found for D. albiventris is higher than previously reported for the species, and other Didelphimorphia. Inbreeding and limited gene flow do not appear as possible explanations for the elevated percentage of anomalies, especially due to the ecological characteristics of Didelphis albiventris. Developmental instability and fluctuating asymmetry could be some of the causes for the anomalies found in this species, mostly since the habitat used by D. albiventris tends to be unstable and disturbed. Dental anomalies were mostly found in areas of the toothrow where occlusion is relaxed or does not prevent teeth from interlocking during mastication, and consequently have no functional value.
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