1. Larger animals are assumed to ingest larger seeds and consume larger fruits, butempirical studies reveal inconsistent trends between body mass and the averagesize of fruits and seeds ingested. Furthermore, no studies have explored seedsize relationships with morphological traits, such as skull dimensions. Such char-acteristics might provide more reliable estimates of ingestion ability and allowfor accurate predictions of seed dispersal capacity in species for which we lackempirical data, especially extinct species. To determine whether (i) mammalianskull dimensions are better predictors of the maximum size of ingested seedsand fruits, compared to body mass and (ii) body mass are the better predictors ofmean fruit and seed sizes, we studied these relationships across three mammalianorders: Chiroptera, Primates and Carnivora.2. We collected novel data on skull dimensions and collated available data on bodymass and maximum and mean sizes of ingested fruits and seeds for mammals(N = 100) across the Neotropics, Asia, Africa and Madagascar. We explored therelationships between anatomical traits and fruit and seed sizes of extant speciesand made predictions for five extinct species.3. Our results revealed that body mass and skull dimensions are essential deter-minants of ingested fruit and seed size in mammals. The latter traits can gener-ate predictions for extinct species, especially coronoid height and maximum jawgape. Nevertheless, body mass predicted larger ingested fruits and seeds thanskull dimensions and explained a greater part of the variance for both maximumand mean sizes in our dataset.