Dense-sampling reveals a complex distributional pattern between the southernmost marsupials Lestodelphys and Thylamys in Patagonia, Argentina

Lestodelphys halli and Thylamys pallidior are southernmost representatives of the Order Didelphimorphia. We analyzed their southern distribution compiling locality records south of 42 degrees S (Chubut and Santa Cruz provinces). We found 87 locality records for L. halli and 105 for T. pallidior. The distribution of L. halli reaches the central plateaus of Santa Cruz province but avoids the northeastern corner of the Deseado Massif. We report the southernmost locality for this species. The eastern and southern distribution of T. pallidior follows the courses of major rivers and coastal areas and it was not found at altitudes >700 m. Its southern distribution is more reduced than in L. halli, not reaching latitudes south of 46 degrees S. We have recorded 20 localities of sympatry between both taxa, all of them from owl pellet samples; however, we have not found conclusive evidence of syntopy by trapping at any site. Both marsupials have widespread distribution in south-central Patagonia with two different histories: one, that of L. halli, related to Patagonian steppes and the other one linked to arid and semiarid lowlands represented by T. pallidior.