Mark A. Norell, a dinosaur paleontologist at the American Museum of Natural History, said the find was “pretty unexpected” and showed “how little we know about the diversity in the dinosaur world.”

Image A sketch of a newly discovered Gigantoraptor dinosaur, compared to a human. Credit... Institute of Vertebrate Paleontology & Paleoanthropology/Associated Press

Dr. Xu’s group said Gigantoraptor was about 300 times as heavy as other similar dinosaurs and stood, at hips and shoulders, twice the height of a man. An examination of marks in the bones indicated that the young animal’s growth rate was considerably faster than that of North American tyrannosaurs, which the scientists said contributed to its giant size.

The scientists reported that “the animal reached its young adult size within seven years and was still at a relatively early young adult stage at the time of death,” which was probably in the 11th year of its life.

Their analysis also revealed “several salient features previously unknown in any other dinosaur,” such as in the vertebrae and the limb bones. The hind limbs were more slender than usual in such robust dinosaurs.

Although no traces of feathers were found, the discovery team noted that smaller oviraptorosaurs are known to have had arm feathers and possibly other types of feathers. It is possible, the scientists said, that Gigantoraptor also retained some arm feathers, “given that the primary function of arm feathers is not to insulate the individual and their development is probably not related to size.”

As Dr. Dodson of Penn explained, large-body animals tend to be naked. Their big concern is not heat loss, but the fact that they generate more heat that must be dissipated. If Gigantoraptor had feathers, they were sparse, as on an ostrich, and also like the ostrich, it might have used them in another heat-related function: courtship displays.