A unique predator in a unique ecosystem: modelling the apex predator from the Late Cretaceous crocodyliform-dominated fauna in Brazil.

ABSTRACTTheropod dinosaurs were relatively scarce in the Late Cretaceous ecosystems of southeast Brazil. Instead, hypercarnivorous crocodyliforms known as baurusuchids were abundant and probably occupied the ecological role of apex predators. Baurusuchids exhibited a series of morphological adaptations hypothesised to be associated with this ecological role, but quantitative biomechanical analyses of their morphology have so far been lacking. Here, we employ a biomechanical modelling approach, applying finite element analysis (FEA) to models of the skull and mandibles of a baurusuchid specimen. This allowed us to characterise the craniomandibular apparatus of baurusuchids, as well as to compare the functional morphology of the group to that of other archosaurian carnivores, such as theropods and crocodylians. Our results support the ecological role of baurusuchids as specialised apex predators in the continental Late Cretaceous ecosystems of South America. With a relatively weak bite force (∼600 N), baurusuchids’ predation strategies likely relied on other morphological specializations, such as ziphodont dentition and strong cervical musculature. Comparative assessments of the stress distribution and magnitude of scaled models of other predators (the theropod Allosaurus fragilis and the living crocodylian Alligator mississippiensis) consistently show different responses to loadings under the same functional scenarios, suggesting distinct predatory behaviours for these animals. The unique selective pressures in the arid to semi-arid Late Cretaceous ecosystems of southeast Brazil, which were dominated by crocodyliforms, possibly drove the emergence and evolution of the biomechanical features seen in baurusuchids, which are distinct from those previously reported for other predatory taxa.View Full Text