The discovery of an unusual 'evil' dinosaur in Patagonia is helping shed light on one of the biggest mysteries in palaeontology – why T-Rex had such small arms. Gualichoshinyae was found to have tiny T-Rex arms despite being on a different family tree to the Cretaceous period's most fearsome predator. This suggests that these unusual limbs did not come from a common short-armed ancestor, but evolved independently, indicating they served some sort of purpose.
Gualicho was discovered in Patagonia's fossil-rich Huincul Formation. It was named after an evil spirit from the Tehuelche culture – Gaulicho was feared and blamed for all bad things that happened.

Scientists from Argentina and the US came across the partial skeleton in 2007. A study describing the species has now been published in the journal PLOS One. The dinosaur was a medium to large theropod – a group that includes T-Rex, Velociraptor and Allosaurus. It would have weighed about 450kg, which is about the same as a polar bear. Yet its arms were about the same size as a human child's.