San Diego

A Chinese dinosaur fossil of immense potential interest to palaeontologists is circulating between private dealers in Europe, highlighting scientists' concern that the underground trade in such artefacts is inhibiting their study.

The fossil of a psittacosaurid is special because it has outer coverings, known as integuments, protruding along the tail, something not previously observed in the dinosaur group to which it belongs. If it were to be established that these protrusions carried hair or feathers, that could mean that most dinosaurs had these features.

Mark Norell, an expert on Asian dinosaurs at the American Museum of Natural History in New York, says the story is a telling example of how private dealings can hide important scientific discoveries. "This specimen could redefine how we look at dinosaurs," he says. "But we can't say, since no one has studied and published on it. It should be returned to China, where it can be studied in a museum."

According to interviews with palaeontologists and dealers, the fossil has made a mysterious journey through Italy and Germany over the past two years. It was last heard of in the hands of a German dealer.

In recent weeks, the fossil has been the subject of extensive discussion on palaeontology websites, prompted by the publication of a painting thought to show a psittacosaurid in the popular book Extreme Dinosaurs by Luis Rey.

There are two orders of dinosaurs: Saurischia and Ornithischia, the latter of which includes psittacosaurids. Some saurischid fossils show integuments, but none have been positively identified on ornithischids, which would make the psittacosaurid specimen an important first.

Last year, the fossil was being kept in a shop called Stone Age in Trieste, Italy. The shop's proprietor, Flavio Bacchia, says that the German dealer, a geologist, had given him the specimen for cleaning. Bacchia says he sent the fossil for study to palaeontologists at Milan's natural history museum.

A museum researcher says that the fossil was examined there in some detail, but that Bacchia then requested its return. Bacchia says he has now returned the fossil to the German dealer, who did not respond to an interview request. Bacchia also says that while the fossil was in Italy, a failed attempt was made to arrange a collaborative study of it with Chinese palaeontologists.