Palaeontologists have recovered the stolen head and feet of one of the world's weirdest dinosaurs. The fossils were somehow smuggled out of Mongolia, but have now been returned. They reveal that Deinocheirus, already known for its massive arms and the hump on its back, had a peculiar skull that looked like a cross between an ostrich and a duck.
In 1965, the first remains of Deinocheirus were found in the Gobi desert by Zofia Kielan-Jaworowska, now at the Institute of Paleobiology in Warsaw, Poland. All she found was a pair of 2.4-metre arms with fearsome claws.
These arms were unlike any seen before, and earned the fossil its name, which means "terrible hands". Kielan-Jaworowska realised the bones belonged to a two-legged theropod, the family that includes Tyrannosaurus rex and birds.
Decades of searching for the rest of the bizarre beast yielded nothing until 2006, when the Korea-Mongolia International Dinosaur Project found a 70-million-year-old skeleton in the Gobi desert. Another followed in 2009. Between them they contained most of the major bones, except the head and feet.
Last year the researchers described Deinocheirus as an ornithomimosaur, or "ostrich dinosaur", a group that includes the Gallimimus featured in Jurassic Park. But at 12 metres long, it was similar in size to T. rex, far larger than any other ornithomimosaur, and had a camel-like hump or sail on its back. However, without the head and feet they were missing key information, including what it ate – although gizzard stones in its stomach hint that it ate plants.
Meanwhile François Escuillié, director of fossil dealership Eldonia in Gannat, France, spotted a strange skull and associated feet in a private European collection. In 2011, he asked Pascal Godefroit of the Royal Belgian Institute of Natural Sciences in Brussels to take a look. Suspecting the bones might be the missing pieces of Deinocheirus, the two checked with the Korean-Mongolian team and found that the skull fit perfectly with the body found in 2006.
It remains unknown how the fossils were smuggled out of Mongolia and made their way to Europe. The collector has not been identified.
Escuillié eventually acquired the fossil and donated it to the Royal Belgian Institute. Then, on 1 May, he and Godefroit presented it to the Mongolian government. The bones will be deposited at the Central Museum of Mongolian Dinosaurs in Ulaanbaatar, along with the rest of the Deinocheirus skeleton, and a Tarbosaurus that was also previously stolen.
The skull shows Deinocheirus was even weirder than palaeontologists had thought. "It looked to me like the product of a secret love affair between a hadrosaur and Gallimimus," says Thomas Holtz of the University of Maryland in College Park. In overall body shape, Deinocheirus was similar to ornithomimosaurs like Gallimimus. The hadrosaur link comes from its snout.
Hadrosaurs are known as "duck-billed dinosaurs" because their snouts were long and flattened. Deinocheirus's mouth has a similar duck-billed shape.