Juliasaurus Paleo artwork, detail, by Mark Witton [© Mark Witton]

THE world was a lot warmer than it is today, with little to no ice surrounding the planet’s poles, a lush and tropical place where the first birds began to evolve for the first time.

Sea levels were 170 metres higher than today that was starting to divide a giant supercontinent of land, creating a perfect habitat for prehistoric predators and hulking herbivores.

And in this late Jurassic period, more than 150 million years ago, a mysterious medium-sized dinosaur – six metres long and weighing around 600 kilos – may have also been thriving.

A theropod fossil, discovered in 2020 in the Morrison Formation in Wyoming, USA, was sold by Mayfair gallery David Aaron to a private collector in 2024.

Nicknamed “Juliasaurus”, scientists have discovered the fossil comes from a dinosaur group predating its distant relative, the Tyrannosaurus Rex, by roughly 90 million years.

And its differing anatomy has baffled some experts who say further tests are required to determine if it is an entirely new species.

It is going on public display at Hollytrees Museum in Colchester, Essex from April 3 in a landmark event that has been partly organised by the David Aaron gallery in Berkeley Square.

The gallery director’s Salomon Aaron said he was “honoured to be a part of the world premiere display of this world-class and potentially groundbreaking dinosaur”, and added: “This specimen is one of the most important dinosaur fossils to have been discovered in North America in recent years, and the collaboration with Hollytrees Museum has the potential to discover an entirely new species.”

The dealership was founded in 1910 and specialises in Greek, Roman, Egyptian, near Eastern, and Islamic antiquities.

Salomon is the fourth generation of the family to run the business that has been involved in some key recent prehistoric scientific breakthroughs.

Last year it said it was involved in the discovery of a new two-legged species, the “Enigmacursor”, a dinosaur from a similar period 152 to 145 million years ago.

The gallery had sold it to a generous private benefactor who agreed to donate the fossil to the museum, allowing further research.

And in 2023 David Aaron exhibited “Chomper”, a rare fossil of a young Tyrannosaurus Rex, with one of the most complete skulls ever discovered.

Pippa Pickles, manager at Colchester Museums, said: “This dinosaur has not been publicly displayed anywhere else in the world, so it is a wonderful and exciting opportunity to view this 6.2-metre-long specimen in the Georgian mansion.

“The remarkable specimen of ‘Juliasaurus’, which may be a new species, further highlights that this globally significant Morrison Formation still has secrets left to discover.”