For 50 years, the dinosaur was just a pair of arms.

But what arms! Each was eight feet (2.4 metres) long, and ended in three eight-inch (20-centimetre) claws. You can understand why the scientists who discovered this beast called it Deinocheirus mirificus, from the Greek for “terrible hand, which is unusual”.

The arms, hands, and shoulder girdle were discovered in 1965 in Mongolia’s Gobi desert, nestled within a 70-million-year-old sandstone formation. But the rest of the skeleton was missing, save for a few uninformative fragments. Palaeontologists have repeatedly ventured into the Gobi to try and find the rest of the animal, but without success.

These failures have turned Deinocheirus into one of palaeontology’s most enduring mysteries. What kind of dinosaur was it? It