More than 100 years after pulling out a skull from a reservoir in Britain, scientists have identified the fossils were of a dinosaur, most ancient relative of Tyrannosaurus rex (T.rex).

The near-complete 30 cm skull of Proceratosaurus, the 165-million-year-old ancestor of T.rex, was uncovered during excavations for a reservoir close to Minchinhampton in Gloucestershire in 1900s.

The fossil was presented to the Natural History Museum, where it is preserved, in 1922.

A team of British and German scientists, including two fossil experts from London’s Natural History Museum, used computed tomography (CT) techniques to generate X-rays and a 3D image of the delicate skull remains.

They found that its teeth, jaws and braincase all closely resemble the structures found in the gigantic predator.

“It was quite a surprise when our analysis showed we had the oldest known relative of T.rex,” said Angela Milner, Museum dinosaur expert.

Initial study of the fossils reveal that Proceratosaurus was much smaller than T.rex, probably about 3m long, and lived 100 million years earlier.

Detailed study of the skull is expected to reveal important clues about the early stages of the evolution of these fearsome predators.

“Fossils collected a century ago can now be studied again with the benefit of much greater knowledge of dinosaurs from around the world,” Ms. Milner said.

“This is still one of the best-preserved dinosaur skulls found in Europe. It is really surprising that it has received so little attention since its original description,” said Oliver Rauhut from the Bavarian State Collection for Palaeontology and Geology in Munich.

“I’m sure that many more tyrannosaurs are still out there to be found. I think we have just scratched the tip of the iceberg so far,” Mr. Rauhut said.

T.rex, one of the largest land carnivores of all time, measuring about 12 m long, lived around 67 to 65 million years ago at the end of the dinosaur era in the Cretaceous period.

The research appears in the Zoological Journal of the Linnean Society.

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