The Telegraph has a good extended look at Eric Prokopi and the trade in illegal fossils:
The law regarding ownership of fossils differs from country to country. In the UK, they are normally treated as “minerals” and, thus, ownership of fossils lies with the person who owns the mineral rights to the land on which the fossil is found. In America, ever since a Sioux rancher won the right to sell fossils found on his land and went on to auction a skeleton of a T. rex, in 1997, for a staggering $8.4million, fossil-hunting has become an expensive activity. Ranchers now sell the rights to any fossils that may be found on their land to the highest bidder.
As, a result, people have started looking farther afield, to countries where the law is not so rigorously applied. Mongolia prohibits the personal ownership of items of cultural significance, such as dinosaur remains, and is also a signatory to a UN convention prohibiting the “illicit import and export of cultural property”. However, an area like the Gobi desert, with its vast, remote landscape, is not only difficult to police but also includes an expanse of sandstone – known as the Nemegt Formation – which is one of the top two dinosaur sites in the world, in terms of diversity of specimens. It has proved irresistible to black-market dealers.