South American Drylands, heterogeneity, adaptation and convergence of small mammals

OJEDA, R. A; DÍAZ, G. B; GIANNONI, S. M.; BORGHI, C. E.; CAMPOS, C. M.; CORBALÁN, V.; TABENI S.; DACAR, M.

Louvain-le- Neuve, Bélgica

Congreso; 8th International Conference Rodens et Spatium; 2002

Aridland were an important scenario in the evolution of the Southamerican mammalian biota. A large proportion of the dryland species (ie. several marsupials, edentates. caviomorph and murid rodents) are not found elsewhere in the New World. In part, this degree of endemism and adaptation to xeric existence is a consequence of evolution in highly heterogeneous and isolated mosaic of drylands in the southern part of the continent since the Oligocene. However. in comparisons with other deserts of the world (i.e. the North American deserts), some of the Southamerican drylands, such as the temperate Monte Desert of Argentina, were regarded, for more than two decades as impoverished in terms of their small mammal species richness and in the repertoire of xeric adaptations when compared with ecomorphological traits such as bipedal locomotion, granivory, water balance and so on. Regarded as paradigmatic features to desert existence. As a result the desert biota that lacked the "kangaroo rat syndrome" were regarded as non-adapted to xeric existence. The "lack of adaptations" of the South American lineage of murid rodents (sigmodontine rodents) has been atributed by some authors, to their relatively recent entrance to South America after the completion of the Panamian bridge, 3.5 million years ago, and to their short time of expossure to arid habitats. Recent studies, however, discard some of these previous notions pointing out the need to be careful when accepting paradigms constructed largely from one continent.