An unassuming-looking fossil that spent 40 years lying forgotten in a drawer has turned out to be the first dinosaur bone ever found in Antarctica.

The specimen was unearthed in 1985, but the team that discovered it was not sure what it was – so it was stored away in the geology collection of the British Antarctic Survey (BAS) in Cambridge.

Now the fossil has been studied by palaeontologists who have confirmed that it is a tail bone from a type of dinosaur called a Titanosaur – this group contained the largest dinosaurs to ever walk the Earth.

The discovery helps to reveal more about how these beasts lived in a part of the world where the fossil record is sparse.

Dr Mark Evans, the collections manager at BAS, recently spotted the fossil amongst thousands of specimens brought back from expeditions to Antarctica over the decades.

“It’s only when you start thinking ‘what’s in this drawer’, that sometimes you come across something and you think, ‘Ah, this looks interesting’,” he said.

The specimen was originally collected on James Ross Island and its discovery was recorded in a field notebook kept by geologist Dr Mike Thomson.

Alongside a tiny, neat sketch of the fossil dated 9 December 1985 he has written “vertebra of large reptile”, noting it was about 10cm wide.

Evans says the team that found it probably thought the fossil belonged to a marine reptile.

But as soon as he saw it, Evans realised the vertebra looked very dinosaur-like. And the date of its discovery meant it would have been the first dinosaur fossil found on the continent.

He called in Prof Paul Barrett from the Natural History Museum (NHM) to confirm his discovery.

“Although it’s not too much to look at, it actually has a really distinctive shape,” Barrett told us, holding the fossil in his hands.

He pointed to a hollow on one end of the fossil and then turned it over to reveal a rounded bump at the other. The vertebrae line up to create a series of ball-and-socket joints running from head to tail.

“As soon as I saw it, I knew what we were dealing with… it was a dead cert we were dealing with a Titanosaur,” he said. “This is a combination of features that’s completely unique to these types of dinosaurs.”

More than 100 species of Titanosaur have now been identified around the world.

All are four-legged plant eaters, with very long necks that helped them reach up into trees and long counter-balancing tails. The very biggest Titanosaurs were more than 115ft (35m) long and weighed about 60 tonnes.

From the size of this tail bone, the scientists estimate the Antarctic Titanosaur was about 23ft (7m) in length.

“Maybe it was a juvenile dinosaur, or maybe it was a genuinely small one – one that was actually bucking the trend for the rest of the group as a smaller adult,” explained Barrett.

This dinosaur would have lived 82 million years ago during the Late Cretaceous Period when Antarctica was very different from how it is today. It would have been covered in lush forest, providing ample food for the plant-eating beast.

The long-forgotten fossil now holds an important place in the history of exploration in Antarctica. Other dinosaur fossils have been found in this remote part of the world in the years after 1985 – but not very many.

Antarctica is a challenging place for palaeontologists to work and the ice conceals the prehistoric record in the rock beneath.

“It shows that an area that we now think is really uninhabitable was once actually very habitable and had this huge cast of characters living on it,” explained Barrett.

“It’s helping us to work out how they fitted into these broader ecosystems at the very bottom of the world about 80 million years ago.”