The evolution of different cranial kinesis types in modern birds has likely driven some spectacular adaptive radiations. However, in certain taxonomic groups, the functional role of new kinesis types remains unclear. This is the case of furnariids, a family of neotropical passerines known for their stunning nest diversity and ecomorphological disparity. These birds exhibit two types of kinesis, each showing different degrees of craniofacial modularity and representing a distinct regime of evolutionary convergence in both beak and neurocranium. Nevertheless, the extrinsic factors shaping the traits associated with kinesis remain unknown. In this study, we assessed correlations between shape, kinesis type, and six ecological variables, alongside the role of kinesis in transitions toward domed nests and open habitats. We found that nest type and diet shaped the evolution of beak and cranial kinesis traits, while diet, foraging behavior, foraging strata, and primary habitat structure influenced neurocranium evolution. Specifically, the emergence of rhynchokinesis predicts the evolution of domed nests and the colonization of less forested environments. We discuss the role of modularity in the association between shape and ecology, the evolution of functional novelties in both kinetic groups, and the hierarchical order of ecomorphological diversity evolution through stages of the adaptive radiation.
Stefanini et al. (Thu,) studied this question.