The bone comes from the tail of a long-necked, plant-eating dinosaur called a titanosaur. Scientists haven’t yet identified the species it belongs to.

It was discovered in 1985 during an expedition to Antarctica’s James Ross Island and was collected by geologist Mike Thomson. Working with the British Antarctic Survey, Thomson was mapping the area’s rock layers and collected marine reptile fossils to help with future dating efforts. He recorded the find as a large reptile.

Decades later, palaeontologist Mark Evans spotted the bone in the British Antarctic Survey’s collections and wondered whether it might be a dinosaur. He and other researchers analysed the shape of the bone and compared it to other more complete dinosaur remains, confirming their discovery.

The findings were published on Monday in the journal Acta Palaeontologica Polonica. Dinosaur fossils are rare to find in Antarctica because of the unforgiving ice caps. But millions of years ago, when this dinosaur lived, the region was populated by lush forests a “rather different and much more hospitable place than we think of today,” said study co-author Paul Barrett with the Natural History Museum in London.

At about 23 feet (7 metres) long, the dinosaur was small for its group and may have been young when it died. Scientists don’t know how the creature met its end, but they think its body floated away from the coast and sank to the sea floor, becoming fossilised in marine rock.