The State of Our Knowledge About Social Knowledge in Platyrrhine Primates: Integrating Decades of Behavioral...

Documenting the extent of social knowledge across primates is critical to understanding the evolution of complex social cognition. While decades of field and experimental research have explored the depth and breadth of social knowledge in catarrhine primates, comparable insights into platyrrhines remain limited. This review synthesizes the current state of knowledge about social cognition in platyrrhine monkeys-a socially, behaviorally, and ecologically highly diverse taxa-integrating observational and experimental work in both field and captive studies to evaluate evidence across four key domains: individual and intergroup recognition, kinship, dominance, and transient social relationships. We assess the presence of egocentric, allocentric, and triadic awareness within each domain, using these frameworks to interpret behavioral data from across the platyrrhine radiation. Although direct tests of social knowledge are rare, emerging evidence from all platyrrhine subfamilies suggests that complex social cognition-such as recognition of third-party relationships and strategic coalition formation-is not exclusive to catarrhines. Playback experiments, relationship-based decision-making, and long-term observational studies indicate that some platyrrhines possess sophisticated social knowledge, though its expression varies with social structure and ecological context. We highlight methodological challenges specific to arboreal taxa and propose future research directions, including the use of emerging technologies and experimental designs tailored to the behavioral ecology of platyrrhines. Our review reveals a field still in its early stages, but one with significant potential to reshape comparative frameworks in primate cognition. By advancing research in underrepresented taxa, we can refine theories of cognitive evolution and better understand the convergent and divergent trajectories of primate social intelligence.