PHYLOGENY OF SOUTHERN SOUTH-AMERICAN MOUSE OPOSSUMS (THYLAMYS, DIDELPHIDAE) BASED ON ALLOZYME AND CHROMOSOMAL DATA

We evaluated the phylogeny of mouse opossums of the proposed genus Thy lamys using 26 enzymatic loci and standard karyotypes in four of the f ive recognized species. Allozyme data were analyzed through parsimony, distance, and likelihood methods. Chromosome data showed a conservati ve diploid and fundamental number in all analyzed taxa (2n = 14, FN = 20), although the FN differed with respect to other forms of small opo ssums by having a FN = 24. Parsimony, distance, and likelihood trees c onfirmed Thylamys as a monophyletic group when compared to other Neotr opical mouse opossums. The recognition of T. elegans at the eastern an d western side of the Andean Cordillera is not supported through alloz yme analyses, validating TATE'S (1933) contention that two species are present. Other reconstructions found T. pallidior to be phylogenetica lly related to ?: elegans from the western Andes of Chile, while ?:ele gans from Bolivia appeared as the most basal thylamyine. Our data sugg est that the latter should again be recognized as a full species, T. v enusta.