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Walking among dinosaurs
By Dan Chinoy (China Daily)
Updated: 2009-11-24 08:02
Sihetun is a nondescript village tucked into the dusty brown hills of western Liaoning province, in almost every respect indistinguishable from countless other farming communities of Northeast China. But it was here 13 years ago that Li Yinfang changed the course of science. Li, a stocky, good-humored farmer with two children, was planting a tree when he noticed something unusual in the ground. With the help of three friends, he carefully unearthed what turned out to be a stunningly well-preserved fossil. About half a meter in length, the skeleton appeared to have a long tail, strong legs, small arms and a head like a miniature tyrannosaurus rex. Along the outside of the body were mysterious black markings, like lines drawn with a charcoal pencil. "I was very surprised because it was very different from the small fish and insect fossils we normally find here. But as ordinary people, we didn't understand it," said Li, 48, who now works as a guide at Sihetun's dinosaur museum. A month after his discovery, Li delivered the fossil to the Chinese Academy of Geological Sciences in Beijing, where paleontologists were also stumped. "We knew it was important. We just didn't know what it was," said Ji Shu'an, one of the scientists who examined the find. Eventually, Ji Qiang, the academy's leading paleontologist, and Ji Shu'an noticed that the markings on the fossil were very similar to those found on remains of the earliest known bird, archaeopteryx. This led them to startling conclusion: Li had discovered the world's first feathered dinosaur.
The fossil, which the two scientists named sinosauropteryx, or Chinese reptile-wing, was the first hard proof of an evolutionary link between dinosaurs and birds for more than a century. "Sinosauropteryx upsets and supersedes the 100-year standing of archaeopteryx as the ancestor to birds," Ji Qiang wrote in Chinese Geology, a scientific journal. The discovery proved that, as well as archaeopteryx, small theropods - a sub-order of small, usually carnivorous dinosaurs - also had feathers. "We realized there is no line, no border" between dinosaurs and birds, said Martin Kundrat, a biologist at the Slovak Academy of Sciences in Bratislava, capital of Slovakia, who is working in Beijing to research the relationship between dinosaurs and birds. "We like to categorize, but evolution didn't work in this way," he said. After the unearthing of sinosauropteryx in 1996, scientists began investigating China's northeastern region for more evidence of feathered dinosaurs. What they found was remarkable. As the world today marks the 150th anniversary of the publication of Charles Darwin's pioneering work on the theory of evolution, On the Origin of Species, experts agree that fossils found in western Liaoning offer some of the most interesting insights into how species evolve. Modern Liaoning is not the most obvious place to look for fossils. At the heart of China's rust belt, the region is best known for its bitterly cold winters, smoke-belching factories and aging industrial cities still reeling from the layoffs that followed the reforms of State-run enterprises in the late 1990s. But about 125 million years ago, most of what would become Northeast China - including Liaoning - and southeast Siberia was a muddy swamp, dotted with lakes and lined to the west with volcanoes in what is today the Inner Mongolia autonomous region. An American scientist dubbed the ecosystem Jehol Biota in the 1920s because it was centered in Jehol, a former Chinese province absorbed by Liaoning, Inner Mongolia and Hebei province in the 1950s. "We had some of the first flowers here and an enormous amount of vegetation," explained Damien Leloup, general manager of Yizhou Fossil and Geology Park near Jinzhou, western Liaoning. "The swamp area made everything grow. There were large numbers of species of birds and hardly any predators. It was fantastic."
The presence of the museum, a joint German-Chinese venture often visited by domestic and foreign specialists, is further evidence of the paleontological importance of the region. Packed with relics, the geology park also boasts one of the best dinosaur fossil casting centers in the world. One of the reasons western Liaoning is so rich in fossils, scientists say, is the combination of ancient lakes, swamps and mud, as well as nearby volcanoes, that made the area exceptionally good for fossilization. "The key component in fossilization is (the body) must be deprived of oxygen within 24 hours," Leloup said There are two ways this could happen: An animal could fall into water and be buried in mud, or could be buried under volcanic ash. If an animal is not buried, the oxygen aids chemical reactions that quickly lead to decay. Exposed or unprotected remains are also easily destroyed by the weather and scavenging animals, he said. Like many dinosaurs, Li's sinosauropteryx likely died in or near one of the region's lakes, where it was quickly buried in mud and fine volcanic ash. Over the next 100 million years, the remains would have been slowly fossilized as the mud and ash slowly compressed into rock underground. It is not clear exactly how the feathers were preserved, but most scientists believe the unusually good conditions for fossilization in the Jehol Biota - conditions that were likely rare outside of what is now Northeast China - played an important role. Along with a remarkable bounty of fossils, including turtles, birds and fish, scientists have identified a host of feathered dinosaur species in the region since Li found sinosauropteryx. "With all those species, you have a relatively clear picture showing how feathers started from a very primitive, very simple structure to a very complex structure," said Xu Xing, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and an expert on feathered dinosaurs.
Some of the oldest feathered dinosaurs, such as beipiaosaurus, a 2-m-tall beaked theropod, had primitive downy feathers, which scientists think were used for insulation. Others, like caudipteryx, which was about the size of a peacock, had unusual tail feathers that may have been used to attract mates or scare predators. Microraptor, a small dinosaur descended from velociraptor, a vicious predator made famous by the Hollywood movie Jurassic Park, also had sophisticated, asymmetrical feathers similar to modern birds. "From the fossil structure, from the bones, if you compare dinosaurs and fossils, including archaeopteryx and sinosauropteryx, they comprise a series - you can see the fossils slowly change," said paleontologist Ji Shu'an. The wide variety of feathered dinosaurs in Liaoning has also led some scientists to speculate that feathers were a more common feature of dinosaurs. "This implied that maybe all relatively recent dinosaurs had feathers. It wasn't just one dinosaur or one species of dinosaur," said Ji. While it is not clear exactly what would create feathers, some experiments have shown that artificially blocking a certain signaling molecule in chickens led to the development of webbed feet and turned scales on their legs into feathers. A similar process may have happened naturally in dinosaurs, changing scales into feathers. This would have given them a vital evolutionary advantage, according to Hu Dongyu, a professor of paleontology at Shenyang Normal University. "The most important function of early feathers was probably insulation," he said and explained that a feathered dinosaur would not have to expend as much energy to keep warm and could instead focus on catching more prey, which would have enabled it to be a more successful species. The fact feathers were later useful for flight was initially probably just a coincidence. But it is unclear precisely how dinosaurs first took flight. One theory is that small, feathered theropods may have moved off the ground into trees, probably to avoid predators and because they were unable to compete effectively for food with bigger animals. "If you live in a tree it's safer because lots of big predators can't get you," Xu said. "Also there is lots of food because you can eat fruits, lots of insects living in trees, and some small lizards and mammals. So this is a good niche for small dinosaurs." Once they moved into trees, feathers may have helped them glide from tree to tree, avoiding larger predators on the ground. Over time, dinosaurs with the strongest wings, best feathers and lightest bones - in short, ones most similar to birds - survived, reproduced and passed on these traits. They evolved into birds. A second theory, however, is that dinosaurs learned to fly by running along the ground and flapping their arms to gain speed. This eventually led to gliding, flight and living in trees. "There's no reason that they had to go up trees to learn to fly. To get into trees is hard. After all, when we humans climb up high, we fall straight down," said Ji. "From our fossil evidence, there is more support for the idea they ran first, because when we look at some of the older fossils, their legs are relatively strong. Their wings are relatively short and the feathers are not totally developed." There was a catch, however. All feathered dinosaur fossils found so far had been dated after archaeopteryx. Scientists called this problem the "temporal paradox": How could birds have evolved from dinosaurs if bird-like dinosaurs appear in the records after birds themselves? Then, last month, experts Xu and Hu published an article describing a four-winged dinosaur similar to microraptor called anchiornis huxleyi. This new find was between 151 and 161 million years old - older than archaeopteryx by about 10 million years. "Now we have this anchiornis that predates archaeopteryx, demonstrating clearly that feathered bird-like dinosaurs are present before the first bird," Xu said. In other words, the anchiornis find showed that holes in the dinosaur-bird fossil record were more likely the result of the sheer rarity of fossilized feathers than problems with the idea that dinosaurs evolved into birds. "The keys of evolution lie in dinosaurs. By studying the past, you understand your current situation," said museum director Leloup. But even Darwin might be startled by what both the evidence and his theory point to. "When you look at a bird, you can say: This is a dinosaur," said Leloup.
 (China Daily 11/24/2009 page7) |
