Xu Xing slouches in his chair, wearing a tracksuit, a child-like smile on his face. Kids love dinosaurs, and so does Xu, 43, one of China's leading paleontologists. He and his colleagues have named dozens of species of dinosaurs so far.
His office at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), at the Chinese Academy of Sciences, is cluttered with books and fossil samples. They had just published an article on Nature earlier this month, announcing the discovery of the largest feathered dinosaur yet found.
"It's very rare that you find large dinosaur fossils so well-preserved and complete," said Xu. Local farmers in Liaoning Province found three specimens in 2009. It took Xu and his colleagues two years to recover the fossils from the rocks and finish the research.
They named the new species Yutyrannus huali, "dinosaur with beautiful feathers." The three specimens, one adult and two young, are estimated to be 125 million years old. The adult dinosaur is nine meters long and weighs over 1.4 tons.
Feathers have been found on small dinosaurs in China over the past two decades, but there has previously been little evidence to support large dinosaurs also having feathers. One hypothesis was that feathers turned into scales on large dinosaurs who didn't need them to keep warm.
"This discovery contradicts that assumption, and the next step we need to figure out the color and the function of the feathers, and how the dinosaur grew that big," said Xu.
Fossils of feathered dinosaurs were found in China in the 1990s. Since then Xu and his colleagues have published dozens of articles in international journals about new discoveries that seem to rewrite the history of avian evolution.
Archaeopteryx, the oldest bird yet found, is recognized as an ancestor of today's birds, but some scientists like Xu believe that modern birds evolved from dinosaurs.
In 2009, they found Anchiornis huxleyi, a species estimated to be more than 150 million years old with feathers covering its arms, feet and tail. In 2011, they found Xiaotingia zhengi, an Archaeopteryx-like theropod, and suggested that Archaeopteryx may not be part of modern birds' lineage, contrary to common belief. It was listed as No. 30 of the 100 Greatest Discoveries of the year by Discovery magazine.
"It's not yet fully recognized, but I'm pretty convinced that birds evolved from dinosaurs," said Xu.
"But there are still many things we don't know, such as the process of evolution, what were the environment and the stimulus for evolution, and that's what we are trying to find out next," he added.
Xu's love affair with dinosaurs is like an unhappy arranged marriage that turned out right in the end. Growing up in Xinjiang, Xu hardly knew anything about dinosaurs when he was assigned to be a paleontology major at Peking University. Nor had his high school teachers ever heard of such a major. They thought it was something high tech, Xu recalled.
In college his interest turned from physics to economics to computer programming, but not paleontology. He then continued to pursue a Master's degree at IVPP, not out of love for the trade, but only so that he could stay in Beijing.
"I was lucky enough to have a mentor who gave me a lot of freedom," said Xu. "He also let me help study some of the very important and rare fossil samples they collected back in the 1960s and 70s." Studying rare fossils piqued Xu's interest and he grew to love his subject.
The first dinosaur fossil discovery in China dates back to the early 1900s, but the country has only recently start to catch up in the field of paleontology and has quickly become one of the most important areas for dinosaur discoveries.
More government funding and booming infrastructure construction have made new discoveries possible, said Xu.
As fossils get more attention, many farmers in areas such as Guizhou, Gansu and Liaoning, who are usually poor, are digging up fossils to sell to private collectors, said Xu.
Xu and his team had to buy fossils from farmers sometimes, usually over 10,000 yuan ($1,586) a piece. "Strictly speaking it's illegal for farmers to dig up fossils, but there's nothing we can do but to buy them especially the rare ones, otherwise they would just be lost," he said.
It's also sometimes difficult to convince local governments who want to keep the fossils to cash in instead of handing them over for research. "This remains one of the biggest problems we face in our line of work," he said.
Xu said that he and his team had been very lucky to have made those important discoveries. "We are probably the luckiest, always seem to stumble upon some interesting fossils," he said.
But it's not pure luck. "It's one thing to find great stuff, but you have to recognize and work out what it is and what it means," David Hone, a British paleontologist who has worked with Xu on a variety of subjects, told the Global Times.
"Xu has a brilliant understanding of all the different complexities of paleontology as a science and so has great insight into spotting solutions to problems and thinking of different and novel implications of some new discovery," wrote Hone.
Xu used to spend at least three months a year in the field. But now he's trying to spend more time at home with his two sons, 12 and 7 years old, who he said have not caught the dinosaur bug. Xu still has to travel frequently from sites to sites and also visit museums to study fossils. The rest of the time he spends sifting through extensive literature and writing papers.
"Research can be quite boring, most of the time you are stuck in this low productivity mode, passive, don't want to work," said Xu. "We are lucky that many of our discoveries are interesting enough to keep us excited longer."
"In paleontology, you never know what you will find," he said, smiling. "Uncertainty is part of the reason I love it."