for National Geographic News
October 6, 2004
A tiny, earlier cousin of Tyrannosaurus rex sported at least a partial coat of hairlike feathers, scientists reported today. The dinosaur chased prey and roamed the lakeside forests of Liaoning Province in northern China some 130 million years ago, researchers said.
Although predicted by several paleontologists, the discovery marks the first time featherlike structures have been directly observed on a tyrannosaurid. Tyrannosaurids are predominantly large dinosaurs with short forelimbs that roamed Earth 130 to 65 million years ago.
"It's the kind of thing we expected, but we thought we might never find a fossil that would justifiably show it," said Mark Norell, who co-authored a paper that describes the new species. The study appears tomorrow in the science journal Nature.
Norell, a curator and chair of the division of paleontology at New York's American Museum of Natural History, said the discovery supports theories that dinosaurs were birdlike, warm-blooded creatures that evolved feathers to stay warm—not to fly.
Researchers named the new dinosaur species Dilong paradoxus
. Dilong derives from Mandarin words meaning "emperor" and "dragon." Paradoxus refers to the unusual feathers found on the 5-foot-long (1.5-meter-long) carnivore.
The research was supported in part by a grant from the National Geographic Society's Committee on Research and Exploration.
Thomas Holtz, a vertebrate paleontologist at the University of Maryland in College Park, was among the group of paleontologists to predict that early tyrannosaurids had feathers. The scientist, who was not involved in the study, said he is thrilled at the latest find.
"There is a lot of attention given to surprises in paleontology," he said. "But there is a side to it where we hope to be scientists, and part of science is based on predictions that are based on the best evidence at hand. It helps to see predictions pan out with discoveries."
The predictions Holtz and other paleontologists have made are based on skeletal data that suggest tyrannosaurids had a more recent common ancestor with birds than did Sinosauropteryx, the most primitive known feathered dinosaur. Sinosauropteryx lived 120 to 150 million years ago.
Holtz noted that, if the early feathers of Sinosauropteryx and the feathers of birds and other feathered dinosaurs are all expressions of the same evolutionary change, "then we have to infer that tyrannosaurids also had some expression of the same trait [feathers]."
"To infer otherwise would be invoking an evolutionary change for which we had no evidence," he said.
Xu Xing of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, is the lead author of the new paper. He said his discovery is significant because it sheds light on the evolution of tyrannosaurids, which include the giant carnivore T. rex.
Tyrannosaurids belong to a broader, diverse group of dinosaurs known as the coelurosaurs. Most paleontologists believe this group gave rise to birds. How this evolutionary change occurred is complex, Xu said. Large tyrannosaurids like T. rex were reportedly covered in scales instead of feathers, suggesting they were distantly related to birds.
With this new find, we can see a perfect evolutionary transition from typical coelurosaurians to highly specialized large tyrannosaurids and clarify a number of questions," Xu said.
In particular, the new specimen's head shares many characteristics with advanced tyrannosaurids, Xu said, whereas its body is of a more primitive, unspecific coelursaurian shape.
Hans-Dieter Sues, the associate director for research and collections at the Smithsonain Institution's National Museum of Natural History in Washington, D.C., agrees. "The new small tyrannosaur definitely shows an interesting mosaic of primitive and derived features; its skull is already more like that of other, later tyrannosaurs than the rest of its skeleton," said Sues, who is a member of the National Geographic Society's Committee for Research and Exploration.
Advanced tyrannosaurid skull features observed in Dilong include teeth and a single nasal bone. (More primitive dinosaurs featured a pair of nasal bones.)
But unlike more advanced tyrannosaurids, Dilong had relatively long forearms with three fingers, the researchers report.
According to Holtz, the University of Maryland paleontologist, the combination of an advanced tyrannosaurid head with a more generalized coelurosaur body is consistent within paleontology.
"For example, the primitive ceratopsian Psittacosaurus—a contemporary, and perhaps prey, of Dilong—shows a head with the initial changes toward the feeding specializations of later horned dinosaurs. Bits [of] its body is a generic herbivore's body," he said.
The description of Dilong paradoxus is based on the fossils of four specimens, including a fragmented one with evidence of protofeathers—precursors to the feathers found on modern birds.
The fragmented fossil went unidentified until a more complete fossil of the same creature was studied and found to match the morphology, or form and structure, of that found in the earlier fragments. The fossils come from a geologic feature in northeastern China known as the Yixian formation, which has yielded several other feathered dinosaurs.
According to Norell, the American Museum of Natural History paleontologist, large adult tyrannosaurs like T. rex probably lacked primitive feathers, an indication that the hairlike structures evolved to insulate warm-blooded dinosaurs rather than to enable flight.
Small animals, Norell said, need insulation to keep warm. Bigger animals no longer need the insulation—a probable reason why animals such as elephants are bald.
"It's doubtful a 40-foot-long [12-meter-long] tyrannosaur was covered with this stuff, if we are right that [the feathers] were needed for insulation. As the dinosaurs get bigger, they need to dump heat, not hold onto it," Norell said.
Xu added that even large dinosaurs like T. rex may have had feathers when they were young. "They are not likely to be completely featherless animals for [their] whole life," he said."
The researchers led by Dr Xu Xing of the Institute of Vertebrate Palaeontology and Palaeoanthropology at the Chinese Academy of Sciences report their findings in this week's issue of the journal Nature.
The "surprising" creature is a tyrannosaurid that lived between 139 million and 128 million years ago, said the researchers.
Small and slender, measuring about 1.6 metres from tip to tail, the creature had the characteristic two powerful rear feet and flesh-ripping teeth made famous by the T. Rex, whose 20-million-year reign ended with the twilight of the dinosaurs some 65 million years ago.
But it had several big differences - it had relatively long arms compared to its big descendant, as well as a long, dragon-like snout, and its scaly skin was covered with a fibrous coat.
Dinosaurs that are believed to have been the ancestors of modern birds had primitive feathery coverings like this.
But in this case, the purpose of the covering was not to provide an evolutionary step for flight but a means to keep warm, the authors suggest.
The skull of Dilong paradoxus (Image: Xing Xu)
"This is the first direct fossil evidence that tyrannosaurids had protofeathers," said the researchers.
The discovery has been called Dilong paradoxus. The first word is a composite of the Chinese "di" (emperor) and "long" (dragon), while the second "refers to the surprising characters of this animal," said the researchers.
The find came from the Yixian Formation in western Liaoning, which has yielded a stunning abundance of unique fossils, many of them described by Xu himself.
A TV show i saw part of, a scientist was talking about feathered dinosaurs and said he sat his kids down and said, "This is very important, listen close--Tyranosaurus rex had feathers!"