Preliminary title:
Palaeoecology and evolution of the carnivorous mammalian faunas of South America from the Late Miocene to the Pleistocene: Insights from stable isotopic signatures (13C, 15N, 18O) in fossil bones and teeth
South America was isolated during most of the Tertiary and developed a very particular mammalian fauna. In contrast to other continents, the carnivore adaptive zone was filled by crocodiles, large snakes and birds, and metatherian mammals (Sparassodonta). The group Sparassodonta was diverse during the Tertiary with a broad range of sizes (≈ 2-50 kg). This diversity decreased towards the late Miocene and the group became extinct at the middle Pliocene (≈ 3 Ma). The cause of this decline and extinction may have been the immigration of placental carnivores to South America (≈ 6-7 Ma ago), which putatively competed with the sparassodonts. This hypothesis was recently criticized and the Ecological Replacement hypothesis was proposed, which postulates that the invading placental carnivores filled ecological niches left empty after the extinction of previous occupants (marsupial carnivores) due to other causes, such as environmental changes. Under the Ecological Replacement scenario, environmental changes should lead to changes in the isotopic relationships among fossil taxa, while in the Ecological Competitive Displacement scenario, similar isotopic relationships should be observable between extinct marsupial predators and the placental predators that replace them.