T. rex's smaller ancestor was covered with down / 130-million-year-old fossils are found in northeast China
Published 4:00 am, Friday, October 8, 2004
Fossil remains of the oldest and smallest known ancestor of Tyrannosaurus rex, the world's favorite ferocious dinosaur, have been discovered in China with evidence that its body was cloaked in downy "protofeathers."
Barely 5 feet long, the beast is a tiny thing compared with T. rex, its monstrous 46-foot descendant. Two examples of the big boy's ancestor -- who has been named Dilong paradoxus, meaning "surprising dragon" -- were found by teams from the Chinese Academy of Sciences in Beijing and the American Museum of Natural History in New York.
The curious features of the primitive little tyrannosaur, some 130 million years old, should provide fresh insights into the evolution of the tribe as the animals became larger and larger, before the ultimate T. was driven to extinction some 65 million years ago along with all the world's other dinosaurs.
One virtually complete fossil plus revealing fragments of another were discovered in the amazingly rich sandstone fossil beds of Liaoning province in northeastern China. They were analyzed by paleontologist Mark Norell of the Museum of Natural History, Xing Xu of the Chinese Academy of Sciences (who now works with Norell in New York) and four colleagues in China.
"A lot of evidence is now piling up about these feathered dinosaurs," Norell said Wednesday, "and it's becoming clear that in the tyrannosaurs and other dinosaurs, the feathers probably evolved first as insulation, for warmth, when the animals were small."
But by the time T. rex had evolved from its ancestral tyrannosaurs like Dilong, it's possible that the huge animals no longer needed true feathers as adults -- and instead were covered with scales because they needed to dump excess heat from their big bodies, very much the way elephants do today, Norell said.
Paleontologist Kevin Padian at UC Berkeley, one of the foremost experts on the evolution of birds and dinosaurs, said the find was important.
"This is the earliest and smallest tyrannosaur yet, so it should give us valuable clues about their evolution into the one we know as T. rex, as well as who their closest relatives were among the other carnivorous dinosaurs," Padian said. "It's interesting that this small one was found with 'protofeathers,' because a painting in National Geographic five years ago pictured a young T. rex with just such a covering. Some people criticized the magazine for speculating without evidence, even though it was a reasonable hypothesis based on what relatives of tyrannosaurs had for coverings. Now, five years later, it's confirmed."
The "protofeathers" -- which show up most clearly in the incomplete fossil -- appear to be single thin filaments with branches and about three- quarters of an inch long, Norell said. And although Dilong's skull was shaped very much like its descendant's, he said its curious forelimbs were surprisingly longer in relation to its body than the stumpy forelimbs of T. rex. But unlike its giant descendant, Dilong's forelimbs held only two fingers instead of three, Norell said.
The layers of volcanic and sedimentary rocks that make up the fossil beds of China's Liaoning province have long been known as extraordinarily rich in the remains of all kinds of long-vanished animals, including fish, birds, insects, dinosaurs and even mammals, Norell said.
In Dilong's time -- between 129 million and 139 million years ago -- the primitive tyrannosaurs must have lived around lakes amid the earliest true flowering plants, in a verdant forest of early conifers much like today's pines and gingkos, Norell said. Then, volcanic ash and sandy sediments covered them all, until modern paleontologists found them.
"But things there are going crazy there now," he said, "because commercial fossil hunters are actually mining the beds for the marketplace while scientists are still finding valuable material for research."