Surprising research in the London Museum of Natural History on the dinosaur Proceratosaurus bradlyi has revealed it to be the ancestor of the famous Tyrannosaurus rex, as opposed to Ceratosaurus as it's name would suggest.
While the animal was first discovered in 1910, it's place in theropod (the family of dinosaurs containing the two legged meat eaters) evolution has been something of a mystery. It was fist identified as being a species of Megalosaurus, as many were back in the day (the name Megalosaurus is often referred to as a 'waste basket' name because of this).
In 1926 it's name was officially recognised as being different to Megalosaurus and given the name Proceratosaurus bradleyi, meaning 'before Ceratosaurus ('horned lizard')', because it was thought to be the ancestor of Ceratosaurus based on the similar horn like crest it had on it's snout.
Now, the latest research suggests that Proceratosaurus was in fact a primitive coelurosaur (the family that contains tyrannosaurs and 'raptors' among others).
It lived around 165 million years ago in the Mid Jurassic (called the Bathonian), some 100 million years before T.rex and was between 3 and 4 metres long (as opposed to T.rex, which was about 13).
Fun fact: Proceratosaurus' name appears on the embryo storage unit and on the map in the tour car in the first Jurassic Park films. It does not, however, appear in person in any of the films.