Low predator competition indicates occupation of macro-predatory niches by giant Miocene reptiles at La Venta, Colombia

Abstract

The La Venta fauna of Colombia (∼13.5–11.5 Ma) represents the most diverse Tertiary locality in the neotropics, with 75 mammal species and a highly non-analogue reptile assemblage containing at least seven testudines and six crocodyliforms. It has been widely hypothesized that the carnivore guilds of South American mammals throughout the Cenozoic were depauperate, potentially due to the continent's isolated history, and that, as a result, non-mammals acted as its dominant predators. Here we test this hypothesis using novel community composition analysis and a model of prey meat availability and competition between carnivorous taxa for prey in different size classes. We find that the carnivorous reptiles account for a very large proportion of demanded biomass, but that, even including reptiles, there was minimal competition for resources among the carnivore guild, relative to competition within modern communities. Further, we evaluate one possible impact of low predation pressure on the herbivores of La Venta through a population analysis of enamel hypoplasia in the notoungulate Pericotoxodon platignathus. At La Venta, mammalian carnivores alone exerted very little predation pressure on the terrestrial community, and our community composition analysis supports the filling of macropredatory niches by crocodyliforms, including both the terrestrial sebecid Langstonia huilensis and semi-aquatic giant crocodylians.