Gargantuavis is an extinct genus of large, primitive bird containing the single species Gargantuavis philoinos. It is the only member of the monotypic family Gargantuaviidae. Its fossils were discovered in several formations dating to 73.5 and 71.5 million years ago in what is now northern Spain, southern France, and Romania. "Gargantuavis" is the largest known bird of the Mesozoic, a size ranging between the cassowary and the ostrich, and a mass of like modern ostriches, exemplifying the extinction of non-avian dinosaurs was not a necessary condition for the emergence of giant terrestrial birds. It was once thought to be closely related to modern birds, but the 2019 discovery of a pelvis from what was Hateg Island (present-day Romania) shows several primitive features.