Gigantoraptor is a genus of large oviraptorosaur dinosaur from the Late Cretaceous Period (85 million years ago). It was discovered in 2005 in the Iren Dabasu Formation in the Erlian basin, Mongolia. It was discerned that this specimen was closely related to the Oviraptor, although much larger. Only one incomplete individual has been found, and from studies of the growth rings, it was determined to be about 11 years old when it died. It was considered a young adult and was still growing. The growth rate of this dinosaur is believed to be one of the fastest growth rates found in theropods.
It is estimated that an adult Gigantoraptor was about 26 feet long and weighed 2.2 tons. It would have been 3 times larger than the largest oviraptorosaur previously known, Citipati. No evidence of feathers were discovered with the remains, but Xu and his colleagues believe there may have been feathers on this dinosaur during its lifetime. The family to which it belongs, Oviraptorosauria, included feathered dinosaurs. The size of the Gigantoraptor would indicate that it relied on body mass as a heat source more than feathers. Those who have studied this species believe that at least arm feathers may have been present on this dinosaur, as arm feathers were not used to regulate body temperature.
The diet of the Gigantoraptor is unknown, but it is possible that it was a herbivore. Some oviraptorosaurs such as Caudipteryx and Incisivosaurus were herbivores. However, it had hind legs that were capable of fast movement and its claws were more readily built for carnivorous abilities. Most herbivores of this size do not have these characteristics.