Morphometric differentiation between Neotropical black-eared opossums, Didelphis marsupialis and D-aurita (Didelphimorphia, Didelphidae)

The Neotropical black-eared opossums comprise two allopatric species that are restricted to forested habitats: Didelphis aurita occurring from northern Argentina to the Northeast of Brazil, mostly along the Atlantic rainforest but also at Araucaria highlands, and D. marsupialis which occurs mostly within the Amazonian rainforest. Their status as separate species or allopatric subspecies has been a matter of debate. We provide an analysis of the morphometric differences between D. aurita and D. marsupialis based on eighteen cranium measurements. An ANOVA between sexes showed sexual dimorphism with males consistently larger than females in both species. Hence, sexes were treated separately. ANOVA between D. aurita and D. marsupialis showed that they are significantly different for 14 and eight characters of females and males, respectively. D. aurita and D. marsupialis were also readily separated by discriminant analysis that correctly classified more than 80 % of the specimens. The squared Mahalanobis distances were slightly higher than five at both sexes. Despite the lack of obvious qualitative morphological characters distinguishing D. all,ita and D. marsupialis, our results show that they are morphometrically diagnosable and should be considered separate species.