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Although several species of dinosaurs with feathers have been uncovered in the rich fossil beds of Liaoning Province, the three largely complete 125 million-year-old specimens are by far the largest.

Fossils discovered in northeastern China of a giant, previously unrecognized dinosaur show that it is the largest known feathered animal, living or extinct, scientists reported Wednesday.

Although several species of dinosaurs with feathers have been uncovered in the rich fossil beds of Liaoning Province, the three largely complete 125 million-year-old specimens are by far the largest. The adult's length was at least 9 meters, or 30 feet, and it weighed a ton and a half, some 40 times the heft of Beipiaosaurus, the largest previously known feathered dinosaur. The two juveniles were a mere half-ton each.

The new species was a distant relative of Tyrannosaurus rex, the mighty predator that lived 60 million years later, at the end of the dinosaur era. The scaly T. rex apparently did not go in for feathers.

In an article in the journal Nature, published online Wednesday, Chinese and Canadian paleontologists said the discovery provided the first "direct evidence for the presence of extensively feathered gigantic dinosaurs" and offered "new insights into early feather evolution."

Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who was the lead author of the paper, said in a statement that it was "possible that feathers were much more widespread, at least among meat-eating dinosaurs, than most scientists would have guessed even a few years ago."

Dr. Xu said the feathers were simple filaments, more like the fuzzy down of a modern baby chick than the stiff plumes of an adult bird. Such insubstantial feathers, not to mention the animal's huge size, would have made flight impossible. The feathers' most important function was probably as insulation.

The species has been named Yutyrannus huali, which means "beautiful feathered tyrant" in a combination of Latin and Mandarin.

Mark A. Norell, a curator of paleontology at the American Museum of Natural History in New York, who had no part in the research, said the findings were significant because they swept aside a longstanding argument that perhaps dinosaurs had feathers only when they were small and shed them as they grew.

Corwin Sullivan, a Canadian paleontologist affiliated with the Beijing institute and an author of the report, noted that the idea of primitive feathers for insulation was not new.

"However, large-bodied animals typically can retain heat quite easily, and actually have more of a potential problem with overheating," Dr. Sullivan said. "That makes Yutyrannus, which is large and downright shaggy, a bit of a surprise."

The researchers suggested that the climate might have been cooler when this feathered giant lived than it was when T. rex roamed in the late Cretaceous period. Not necessarily, said Dr. Norell, who pointed out that large, hairy mammals like giraffes and wildebeest, perhaps analogous to feathered dinosaurs, live today in hot latitudes.

Another possible explanation, offered by the authors of the journal article, is that the feathers were not widely distributed over the dinosaurs' bodies, and so their function as display plumage cannot be ruled out. Yet the researchers noted several times that the feather covering was extensive and "densely packed," resembling some recent discoveries of fossil birds "that undoubtedly had plumage covering most of the body."

"This is a great time to be a dinosaur paleontologist," said Dr. Norell, whose research concentrates on fossils from China and the Gobi Desert of Mongolia. "The feathered dinosaurs show how the whole conception of dinosaurs has really changed in the last 15 years."