Sparassodonta vs. Carnivora: ecological relations between carnivorous mammals in south america.

PREVOSTI, F; FORASIEPI, A.; SOIBELZON, LEOPOLDO; ZIMICZ ANA N.

Mendoza

Congreso; 10th International Mammalogical Congress; 2009

SAREM

South America was isolated from other continents during most of the Tertiary, developing a very particular mammalian fauna. In contrast to other continents, the carnivore adaptative zone was filled by crocodiles (Sebecidae), large snakes (Madtsoiidae), large birds (Phorusrhacidae), and metatherian mammals (Sparassodonta). Sparassodonta was diverse during the Tertiary and comprised a broad range of sizes (≈ 2-50 kg). This diversity decreased towards the late Miocene (Huayquerian) and the group became extinct at the middle Pliocene (≈ 3 Ma, Chapadmalalan). Several authors have suggested that the cause of this decline and extinction was the ingression of placental Carnivores to South America (about 6-7 Ma ago), because they putatively competed with the Sparassodonta. This hypothesis was criticized in recent years. With the intention of testing the hypothesis of ?competitive displacement?, we review the fossil record of South American Sparassodonta and Carnivora, collect data about diversity, first and last appearances, and estimate size and diet of the involved taxa. The diversity of Sparassodonta is low relative to that of Carnivora all along the Tertiary. The highest number is found in the early Miocene (Santacrucian), with more than 10 species. The fossil record shows overlap of groups during the late Miocene-middle Pliocene, and the Sparassodonta?s richness curve declines since the first record of the Carnivora during the Huayquerian. Despite this overlap, carnivores were represented by 4 or less species during the late Miocene-Pliocene, and their diversity reached values of about 20 species only in the early Pleistocene (Ensenadan). Moreover, Carnivora was first represented by small-sized, omnivore species, with large omnivores first appearing in the Chapadmalalan. During this period, Sparassodonta was represented by large and small hypercarnivores and a single large mesocarnivore species. These data suggest that factors other than competitive displacement may have caused the extinction of the Sparassodonta.