Paleodiet and niche breadth in Middle Miocene rodents and ungulates from northern South America revealed through stable isotope analyses

Abstract

Reconstructing ecological interactions within extinct vertebrate communities remains challenging, particularly for taxa such as South American native ungulates (SANUs) and caviomorph rodents that lack modern analogs. The Middle Miocene site of La Venta in Colombia hosts one of the most diverse tropical vertebrate assemblages in South America, but little is known about the paleocological interactions of its taxa. We present stable isotope (δ13C and δ18O) analyses of fossil tooth enamel from SANUs (n = 51) and caviomorph rodents (n = 16) to reconstruct paleodiet and niche partitioning. Minimal diagenetic alteration was confirmed using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy. All taxa exhibited C₃-dominated diets, consistent with forested tropical environments. However, inter-taxon isotopic variation revealed ecological differentiation: Miocochilius anomopodus (a typothere notoungulate) showed the narrowest niche breadth and highest δ13C values, suggesting occupation of more open habitats, while astrapotheres, toxodont notoungulates, and litopterns displayed broader niches indicative of closed-canopy forest browsing. The two rodent taxa showed distinct δ13C values despite morphological similarities, supporting niche differentiation within sympatric caviomorphs. These results provide the first isotope-based evidence for resource partitioning among Middle Miocene neotropical herbivores from Colombia and support paleoenvironmental reconstructions of La Venta as a heterogeneous mosaic of mainly forested areas with open habitats adjacent to large water bodies that hosted some of the largest vertebrates during the Miocene in South America.