French palaeontologists have unearthed a giant thigh bone from a 50-tonne dinosaur in a so-called Jurassic Park graveyard near the city of Cognac.

In one of the largest finds in Europe, the National History Museum of Paris’ Ronan Allain said the find was a “major discovery”.

“I was especially amazed by the state of preservation of that femur.

“These are animals that probably weighed 40 to 50 tonnes,” he said.

Mr Allain marvelled at the integrity of the bone, being able to see the insertions of muscles, tendons and scars.

“This is a very rare find as large pieces tend to collapse on themselves, to fragment,” he told French news website The Local.

Jean-François Tournepiche, curator at the Angouleme Museum, added: “This femur is huge! And in an exceptional state of conservation. It’s very moving.”

Volunteer excavators found the bone at the paleontological site of Angeac-Charente in south western France. Photo: Getty

The two-metre femur at the Angeac-Charente site is thought to have belonged to a sauropod, herbivorous dinosaurs with long necks and tails which were widespread in the late Jurassic era, more than 140 million years ago.

Mr Allain said scientists at the Jurassic site have found more than 7500 fossils of more than 40 different species since 2010.

-with AAP