Gargantuavis is a genus of extinct avialan stem- birds containing the single species Gargantuavis philoinos. G. philoinos lived during the late Cretaceous period in what is now southern France. Its fossils were discovered in the Marnes Rouges Inferieures Formation, which has been dated to roughly 70 million years old. A large avialan, Gargantuavis was flightless, occupying an ecological niche somewhat similar to that of modern ratites or more primitive theropods. It is possible that some of the fossil eggs found in the region, usually attributed to non-avialan dinosaurs, actually belong to this bird.