Vegetation Partitioning among Lujanian (Late-Pleistocene/Early-Holocene) Armored Herbivores in the Pampean Region

Abstract

The majority of the fossils of Lujanian Land Mammal Age are recovered from Pampean Region sediments of the Guerrero member of the Lujan Formation (c. 20,000 yr BP-8,500 yr B.P.). A dry, cool climate occurred in the Pampean Region with climatic conditions similar to the climate today in Northern Patagonia. The vegetation has been interpreted as a psammophytic steppe. The Luján local fauna is impressive for its abundance of large herbivores. There are about 30 species of herbivorous mammals ranging from approximately 50 kg to several tons, more than half of them edentates. Within them, the armored forms (Cingulata) are predominant. The coexistence of so many large herbivores in such a poor environment suggests strong competition for resources. Here I analyze plant resource exploitation among sympatric Lujanian herbivorous armored xenarthrans. Morphofunctional studies reveal that the main dietary differences among these cingulates were in the degree of coarseness of the vegetation they were capable of processing. While the eutatine is mainly a browser, the larger pampatheres (up to 200 kg) and glyptodonts (between one and two tons) represent increasing degrees of grazing habits. Morphometric and morphofunctional studies currently in progress suggest that the smaller glyptodonts had more browsing habits, while the larger are proposed to have grazed to a greater extent. This scenario may be applicable to other herbivores.