The natural history museum in Maastricht wants France to return the giant fossilised skull of a lizard taken by French troops as booty during the siege of Maastricht in 1794.

Mosasaurus hoffmanni, which has been on show at the Musée National d’Histoire Naturelle in Paris ever since, is the biggest of the giant sea lizard species ever found. Its jaw measures more than a metre and the animal is thought to have been between 10 and 15 metres long.

Several fossils of sea lizards were found in the marl caves around Maastricht in the 18th century and the example stolen by the French is the biggest and most important.

French naturalist Georges Cuvier found out that the 66 million-year-old skull belonged to probably one the last of the giant lizards before it became extinct.

“It is an iconic object in paleontology. You could compare it to what Tutankhamun is to archeology,” paleontologist John Jagt told broadcaster NOS. “This fossil put the idea into the heads of the scientists of the 18th century that plants and animals could become extinct because of natural circumstances. Every mosasaurus found since has been compared to the one in Paris.”

The Maastricht natural history museum, which has a replica of the skull, was lent the original skull in 2009 for a special exhibition but could not persuade its French counterpart to make it permanent.

The museum makes no bones about the fact that the fossil, which was declared a part of French heritage even before it arrived in Paris, was stolen and says so in its  display.

“We would like to have it back,” director Wim Hupperetz said. “It’s an icon for Maastricht and the Netherlands. We are busy looking at claims from abroad and returning art but it should also work the other way around. Things were taken from the Netherlands as well, in times of war as is the case here, and we want them back.”

Hupperetz is meeting representatives of the local council and the education ministry to set the wheels in motion for an official request to return the skull on Thursday.

Mosasaurus, which date from the end of the dinosaur era, swam in the shallow tropical seas which covered southern Limburg some 67 million years ago. Its name means lizard of the Meuse River