Paleoecology 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

南美洲在第三纪的大部分时间里都是与世隔绝的，并形成了一个非常特殊的哺乳动物群。与其他大陆不同的是，食肉动物的适应区充满了鳄鱼，大型蛇和鸟类，以及后生哺乳动物（Sparassodonta）。在第三纪，Sparassodonta是多种多样的，具有广泛的大小范围（102 -50公斤）。这种多样性在中新世晚期逐渐减少，在上新世中期（103 Ma）灭绝。这种下降和灭绝的原因可能是胎盘食肉动物移民到南美洲（106 -7 Ma前），它们与sparassodonts竞争（生态竞争置换假说，ECD）。这一假说最近受到批评，并提出了生态替代（ER）假说，该假说假设新来者（胎盘食肉动物）填补了由于其他原因（如环境变化）而导致先前居住者（有袋类食肉动物）灭绝后留下的空白生态位。这个问题目前正在研究使用形态测量学，然而，这可能是有偏见的系统发育信号。在这里，我们建议使用稳定同位素（13 C，15 N，18 O），以补充研究的食肉动物行业协会在晚新生代在阿根廷的演变。这种纯粹的表型方法将产生关于实际生态变化的直接信息。在ER的情况下，环境的变化应导致化石类群之间的同位素关系的变化，而在ECD的情况下，类似的同位素关系，应观察到灭绝的有袋类捕食者和胎盘捕食者，取代他们。

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). 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 immigration of placental Carnivores to South America (≈ 6-7 Ma ago), which putatively competed with the sparassodonts (Ecological Competitive Displacement Hypothesis, ECD). This hypothesis was recently criticized and the Ecological Replacement (ER) hypothesis was proposed, which postulates that newcomers (placental carnivores) filled ecological niches left empty after the extinction of previous occupants (marsupial carnivores) due to other causes, such as environmental changes. This subject is currently being studied using morphometrics, which, however, may be biased by a phylogenetic signal. Here we propose using stable isotopes (13C, 15N, 18O) to complement the study of the evolution of the carnivore guild during the late Cenozoic in Argentina. This purely phenotypic approach will yield direct information on actual ecological changes. Under the ER scenario, environmental changes should lead to changes in the isotopic relationships among fossil taxa, while in the ECD scenario, similar isotopic relationships should be observable between extinct marsupial predators and the placental predators that replace them.