Prosauropods are basal sauropodomorphs that were the major terrestrial faunal components from the Norian until their extinction during the Toarcian. Their status as a natural group is debatable. In the present work I describe Adeopapposaurus mognai, a new sauropodomorph from the Cañón del Colorado Formation, in northwestern Argentina. Diagnostic autapomorphies and combination of characters of Adeopapposaurus include a series of large foramina in a sub-vertical row on the lateral surface of the premaxilla; strongly rugose depression bordered by a protuberance with a series of foramina in a sub-vertical row, on the lateral surface of the anterior end of the dentary; eleven anteroposteriorly elongated cervical vertebrae and thirteen dorsal vertebrae with neural arches taller than the respective centra. Phylogenetically Adeopapposaurus is resolved as the sister group to Massospondylus; differing from the latter based on differences in mandible and premaxilla and addition of one dorsal vertebra to the neck. The specimens described here reveal numerous herbivorous adaptations, including the presence of a highly vascularized bony plate in the premaxilla and dentary, which indicates that it had a horny beak.