Ernesto Brunetto

Mylodon darwini Owen (Xenarthra, Mylodontinae) from the Late Pleistocene of Mesopotamia, Argentina, with remarks on individual variability, paleobiology, paleobiogeography, and paleoenvironment

ABSTRACT The subfamily Mylodontinae, typified by Mylodon, is known from the Colloncuran (late Miocene of Patagonia, Argentina) to the late Pleistocene of South America and North America. Mylodontinae have been recorded during the Pleistocene of Argentina, including the genera Glossotherium, Paraglossotherium, Lestodon, and Mylodon, with Paraglossotherium and Mylodon not as well known as the other genera. In Argentina there have been traditionally four species of Mylodon, M. darwini, M. zeballozi, M. listai, and M. insigne, although the validity of some has been considered doubtful. A nearly complete skull with an associated mandible of Mylodon darwini from the late Pleistocene of Mesopotamia, Argentina, is described. The specimen represents the first record of the species in the Mesopotamian region. The morphometric analysis indicates that M. darwini had greater individual variability than previously thought. Although based on the results of the morphologic and morphometric analysis, the idea of sexual dimorphism for M. darwini is, for the time being, unwarranted. This new record also supports the idea that Mylodon had great ecological tolerance and was capable of inhabiting climates ranging from cold and arid to warm and humid, and even montane environments.

Planation Surfaces on the Paraná Basaltic Plateau, South America

SRTM data constituted a good resource for morphometrical analyses of the extensive Parana Basaltic Plateau (southern Brazil and northeastern Argentina, South America). The plateau is a stepped system of high-level surfaces separated by escarpments and with incised fluvial valleys, mainly belonging to the Upper Parana and the Upper Uruguay River basins. Palaeosurface remnants of such basins preserve attributes that have been identified in digital elevation models. Generation of hypsometric curves in six representative tributary basins of the Uruguay River basin and also in one tributary basin of the Parana River in the region permitted to identify, classify and map the main Cenozoic planation surfaces of the basaltic plateau. Other morphometric parameters such as longitudinal profiles and isobase lines were produced also to delimit such surfaces. Field geomorphological analyses were performed, also including the description of toposequences. Three groups of hypothetical hypsometric curves are deduced from proximal value sets for predicted base levels. Each mapped surface was considered between the minimum height for correlative surfaces in all of the subbasins and the minimum height of the next higher surface. Using that approach, which is based on the clustering from the modelled base level in the river mouth of the subbasins, three main palaeosurfaces were defined in northeastern Argentina. Complementarily, three intermediate or secondary surfaces also were identified based on morphometric analyses, taking into account that small flat remnants at the same level suggest that they could be remnants of a formerly extensive plain.

An intertropical opossum (Mammalia, Marsupialia, Didelphidae) from the late Middle–Late Pleistocene of austral South America

Abstract The record of an opossum is reported here coming from a Middle–Late Pleistocene fluvial sedimentary sequence outcropping in the austral Chaco geomorphological region, Santa Fe province. Despite this family has different living forms widely distributed in South American plains, with great tolerance to diverse habitats conditions, the Pleistocene occurrence of didelphoids is very scarce and only limited to Holocene deposits sensu lato from austral pampean plains. The specimen found represents at the moment the only Pleistocene didelphoid opossum from Argentina with an accurate stratigraphical context. In a taphonomic framework, MFA-Pv 1582 shows no evidence of abrasion produced by transport, probably resulting of a very short time-transport. This intertropical form of Didelphis genus from Pleistocene sequences displays undoubtedly novel and sustancial paleoenvironmental and ecomorphological conditions to test in the austral Chaco region. Although the specimen shares a generalized didelphoid form, some morphologies in the humerus are closer with arboreal habits. In this context, added to the sedimentological and stratigraphical framework, it’s possible to suggest that subtropical conditions with some woodlands and wetlands dominate the provenance region of the fossil material, over a late Middle–Late Pleistocene interglacial period.