To investigate the origins of social cognition, we need to look beyond the human species. Investigations within primates constrain us to a linear understanding of evolution. Dogs have emerged as an alternative animal model because our last common ancestor with them dates back 95-100 million years. They have advanced socio-cognitive skills, even when discounting recent domestication effects, not present in many other mammals, suggestive of convergent rather than linear evolution. Moreover, they can be trained to perform awake and unrestrained functional magnetic resonance imaging. To better understand convergent evolution of social cognition, we conducted fMRI in 36 healthy pet dogs and 42 human adults, investigating neural processing of social interactions with largely identical scanning and experimental parameters. Dogs and humans viewed social interaction videos between dog or human agents, as well as non-social agent-object interactions. Dogs show specific activation patterns for social compared to non-social stimulus observations, in particular higher involvement of rostral sylvian, suprasylvian and ectosylvian gyri bilaterally, which have been linked to facets of action and agent processing. In terms of eyetracking, dogs showed longer visual engagement with social than non-social stimuli, indicative of a stronger relevance and salience of social than agent-object interactions for dogs. A higher number of saccades in the social interaction videos, in particular in the dog-dog interactions, can be linked to turn-taking, or dialectic, processing of social interactions.Our findings showcase communal and distinct aspects of social interaction processing across the mammalian lineage, increasing our understanding of how different brains produce similar behaviors.