Stable isotope analyses are powerful tools for reconstructing ancient ecologies and ecosystems, as they provide direct insights into dietary ecology independent of morphology. The application of stable isotope analyses, however, is not without limitations, as determination of food web dynamics using these methods often relies on poorly tested assumptions. In this presentation, I will address challenges in paleoecological reconstructions of South American tropical ecosystems. By testing long-standing assumptions of stable isotope analyses, I aim to validate the suitability of applying these techniques to different mammalian clades, and to more reliably interpret the isotopic signals preserved in extinct organisms.