Abstract

We evaluated the phylogeny of mouse opossums of the proposed genus Thylamys using 26 enzymatic loci and standard karyotypes in four of the five recognized species. Allozyme data were analyzed through parsimony, distance, and likelihood methods. Chromosome data showed a conservative diploid and fundamental number in all analyzed taxa (2n = 14, FN = 20), although the FN differed with respect to other forms of small opossums by having a FN = 24. Parsimony, distance, and likelihood trees confirmed Thylamys as a monophyletic group when compared to other Neotropical mouse opossums. The recognition of T. elegans at the eastern and western side of the Andean Cordillera is not supported through allozyme analyses, validating TATE'S (1933) contention that two species are present. Other reconstructions found T. pallidior to be phylogenetically related to T. elegans from the western Andes of Chile, while T. elegans from Bolivia appeared as the most basal thylamyine. Our data suggest that the latter should again be recognized as a full species, T. venusta.