In the last decades several new dinosaurs species have been described from both Laurasia and Gondwana and a complex, multi-dimensional picture of the physiology, evolution and behavior of dinosaurs has emerged. One of the central elements of new discoveries is the recognition of a complex sociality in this vertebrate clade, especially in herbivorous taxa. Herbivores are not genetically provided with the enzymes needed to break down and metabolize cellulose, thus need gut symbiotic bacteria communities, able to digest plant-derived materials. In this short contribution, we discuss the hypothesis that precisely the need to horizontally exchange bacteria among individual ls of different ages, has triggered a growing sociality in herbivorous dinosaurs.