A multi-isotopic study reveals the palaeoecology of a sebecid from the Paleocene of Bolivia

Sebecids constitute a family of notosuchian crocodylomorphs of probable terrestrial habits. They are notable for having survived the Cretaceous-Paleogene mass extinction and are known until the Miocene in South America. However, ecological traits that favoured their resilience in continental ecosystems remain unknown. Here, using a multi-isotopic approach, we infer several palaeoecological traits of a sebecid from the locality of Tiupampa (Bolivia), which contains a diverse vertebrate fauna of the Early Paleocene. After having constrained the effects of diagenesis, the study of the oxygen isotope compositions of apatite phosphate allows the identification of water resources for the various studied taxa and to infer an ectothermic thermoregulation strategy for the sebecids. A terrestrial lifestyle is also supported by different oxygen isotope compositions observed between sebecids and aquatic dyrosaurid crocodylomorphs. The radiogenic strontium isotope compositions confirm the continental affinities of this fauna, with no marine input in the palaeoenvironment frequented by the different faunal elements. The calcium and carbon isotope compositions show that the sebecids from Tiupampa were at the top of a C3-based food web. Finally, a local dry environment with tropical temperatures for those specimens is inferred both from oxygen and carbon isotope compositions of their hard tissues.