After sitting idly in a Paris history museum for more than 80 years, a previously overlooked fossil is shedding light on a decidedly obscure chapter in dinosaur evolution. Not only is the new species providing scientists with new clues, it has turned out to be the earliest relative of a certain long-necked plant-eater called the Brachiosaurus.

In 1934 paleontologists came across a dinosaur fossil in the village of Damparis in eastern France. A species was not immediately identified and the fossil was mostly ignored by scientific literature in the 30s and 40s, referred to only as the "Damparis dinosaur." But now scientists from Imperial College London, together with France's Museum National d'Histoire Naturelle, where Damparis has been stored, and Université Paris 1 Panthéon-Sorbonne, have pulled it out for another look.

New analysis of the fossil has revealed it to be a brachiosaurid sauropod, a group belonging to a larger group of dinosaurs called the titanosauriforms. These were some of the biggest creatures to ever live on land and roamed the Earth from at least the Late Jurassic (around 160 million years ago) to the mass-extinction event at the end of the Cretaceous period (65 million years ago).

The researchers say that the age of the fossil, which has now been named Vouivria damparisensis, is around 160 million years old. This is significant for a couple of reasons. It makes it the earliest known fossil from the titanosauriform family and therefore the earliest relative of the brachiosaurus, and helps to fill in what was a sizable hole in the existing fossil records.

"Vouivria would have been a herbivore, eating all kinds of vegetation, such as ferns and conifers," says Imperial College London's Dr Philip Mannion, lead author of the study. "This creature lived in the Late Jurassic, around 160 million years ago, at a time when Europe was a series of islands. We don't know what this creature died from, but millions of years later it is providing important evidence to help us understand in more detail the evolution of brachiosaurid sauropods and a much bigger group of dinosaurs that they belonged to, called titanosauriforms."

The scientists say Vouivria died at a young age, weighing around 15,000 kg (33,000 lb) and measured more than 15 m long (50 ft), around 1.5 times the size of a double-decker bus in the UK. It had a long neck, a long tail and four legs of equal length.

Without many fossils to work with, it has been hard for scientists to plot the evolution of the titanosauriforms and their spread across the planet. But already Vouivria is starting to fill in some of the blanks. The team believes that the dinosaur died in a coastal lagoon in the midst of a short sea level decline in Europe, and was then buried when the sea rose again.

Working the new evidence into analysis of brachiosaurid evolution, the scientists now believe that the creatures were most likely extinct in Europe soon after this creature lived – by the Early Cretaceous period – and restricted to what is now Africa and the USA. They are now expanding that analysis to consider the evolutionary relationships between all members of the titanosauriform family to understand their evolution even further.

The research was published in the journal PeerJ.