Trophic relationships among Lujanian mammals 30 years later: brief review and the example of the Arroyo del Vizcaíno Local Fauna

The structure of trophic interactions in extinct communities is a key aspect of palaeoecological reconstruction. Three decades after its initial publication, the thermodynamic model proposed for the Lujanian (late Pleistocene–early Holocene) South American megafauna is revisited here, considering its legacy, criticisms, and further developments. The model, based on Damuth’s inverse relationship between body mass and population density, had suggested an energetic imbalance in the classical Luján Local Fauna: insufficient primary productivity for herbivores and an apparent excess of prey biomass for carnivores. Some criticisms focused on assumptions regarding metabolic rates and diet composition. We assess these concerns in light of new evidence and apply the model to the Arroyo del Vizcaíno Local Fauna (AdV, Uruguay), a rich and minimally time-averaged assemblage of Lujanian megafauna. Updated estimates of body mass, population density, and energetic requirements confirm the previous imbalance pattern, suggesting that some taxa. especially among ground sloths, may have included significant animal matter in their diet. A sensitivity analysis varying the field metabolic rate and assimilation efficiency shows that this pattern is robust across a biologically plausible parameter space. Although uncertainties remain, particularly regarding digestive physiology and local productivity, the results underscore the value of thermodynamic constraints for understanding extinct ecosystems. This integrative approach offers a testable framework to explore community structure and the ecological roles of now-extinct taxa in megafaunal systems worldwide.