This guy was not playing by the rules.

Most theories of dinosaur evolution say that carnivorous dinosaurs, the ancestors of today’s birds, got smaller as they became more bird-like. But the remains of a new species and genus of dinosaur, discovered in Inner Mongolia and announced at a press conference in Beijing this morning, throw a wrench into that idea.

Gigantoraptor, as he has been named, is surprisingly bird-like in his skeleton, and probably had feathers. He lived in the Late Cretaceous about 70 million years ago, and an analysis of his skeleton puts him in the same family as the beaked, bird-like Oviraptor, say Xing Xu of the Chinese Academy of Sciences, who led the discovery, and colleagues. By all rights, a birdlike dinosaur should have been evolving toward the size of birds living today—if not crows, then at least emus.

Gigantoraptor stood about 3.5 meters (10 feet) high at its shoulder, twice the height of a person today. He stretched 8 meters (24 feet) in length and weighed in at 1,400 kilograms (3,000 pounds). Or, in an artist’s conception,

Artist's reconstruction of Gigantoraptor with much smaller feathered ornithomimids. Credit: Zhao Chuang and Xing Lida/IVPP

 (Our boy is the dino on the far left.)

From lines of arrested growth on the fossilized bones, the paleontologists infer that this specimen was still a young adult when he died, meaning the full-sized adults may have been even bigger. Other feathered dinos rarely grew larger than about 40 kilos. One explanation is that Gigantoraptor’s growth rate considerably surpassed that of the large North American tyrannosaurs, but that just shifts the mystery to why the growth rate was so fast. All paleontologists can say at this point is that the evolution from beasts like T. rex—and now Gigantoraptor—to robins and hummingbirds was not a smooth linear progression from huge to small, but instead took numerous anatomic detours along the way.