From their origin in the Middle Jurassic until the present, birds have undergone one of the most important evolutionary radiations among vertebrates, with the development of great species-level diversity and the occupation of a broad spectrum of ecological niches. Since dietary shifts involve a series of morphophysiological adjustments and reflect the use of the resources, diet represents a key ecological and evolutionary parameter to understand the history of bird clades. This study combines neontological and paleontological dietary information in a phylogenetic context, aiming the understanding the role of feeding habits in bird evolution and their potential relationship with past ecological and evolutionary events. Our findings point towards an omnivorous ancestral diet for the avian clade, which is consistent with dietary information, dental structure and life style of the first birds, such as Archaeopteryx. Our results also show dietary shifts in avian evolutionary history. Faunivores predominate in the avian history, while herbivorous lineages underwent adaptive radiations possibly related to transformation of ecosystems and their plant assemblages worldwide such as the development of the angiosperms during the Cretaceous or the development of grassy environments in the Oligocene. Faunivorous and herbivorous clades arose basically through diversification within lineages, while omnivores evolved due to transitions into the strategy. The capacity to specialize and generate new trophic niches allowed faunivores and herbivores to diversify more than omnivores. Nevertheless, despite this relatively low diversification, the omnivorous strategy appears to be key to the primary processes of bird radiation and fundamental in the evolutionary success of birds.Peer reviewe
