Champsosaurs, gharials, and the functional ecomorphology of resource partitioning

Understanding how species interact and partition ecosystems is central to ecology and evolution, yet this remains difficult to test in the fossil record. Here, we examine potential resource partitioning between the Late Cretaceous diapsid Champsosaurus lindoei and the alligatoroid Leidyosuchus canadensis, two sympatric semi-aquatic predators from the Dinosaur Park Formation of Alberta, Canada. To interpret their ecological interactions, we compare them with the most analogous extant pair, the gharial (Gavialis gangeticus) and mugger crocodile (Crocodylus palustris), whose coexistence and dietary differences are well documented. Using three-dimensional reconstructions of skulls and jaw musculature, we estimate ecomorphological performance metrics—including bite force, mandibular inertia, and bite duration—validated against the extant predators. Results show that Champsosaurus and Leidyosuchus differed in tooth and skull morphology, mandibular inertia, and bite performance in ways closely paralleling those values for Gavialis and Crocodylus. The estimated ecological distance between both pairs of taxa is also broadly similar. These findings confirm that Champsosaurus occupied a more specialized piscivorous niche, while Leidyosuchus was a generalist predator. Moreover, our approach demonstrates that functional morphology can reveal degrees of resource partitioning in deep time when anchored to extant analogues, providing a framework for reconstructing the ecological structure of ancient communities.