Endozoochory is an essential plant-animal interaction in tropical forests, involving the swallowing and defecation of seeds. To better understand whether anatomical traits (i.e. body mass and skull dimensions) are good predictors of seed dispersal in mammals we studied the relationships between morphology, fruit and seed size and seed dispersal distance across three orders: Chiroptera, Primates, and Carnivora. Our results revealed that body mass is an important driver of the size of ingested seeds for all orders and of the seed dispersal distance produced by Primates. In addition, the distance between the molars, jaw length, and jaw gape are good predictors of the size of ingested seeds. These results show how body mass and cranial anatomy constrain ingested seed size and dispersal distance across mammals and reinforce the importance of maintaining functional diversity in seed dispersers to maintain tropical forest structure and regeneration.