Bernissart Iguanodons: The 1878 Belgian Coal Mine Discovery

The Bernissart Iguanodons are a group of at least 38 dinosaur skeletons found in 1878 by coal miners working some 322 metres underground at Bernissart, in the Belgian province of Hainaut. Recovered between 1878 and 1881 and studied by the palaeontologist Louis Dollo in Brussels, they gave scientists their first complete skeletons of a dinosaur. The find overturned earlier guesses about what Iguanodon looked like and remains one of the most remarkable dinosaur discoveries ever made.

Background: Iguanodon before Bernissart

Iguanodon was one of the first dinosaurs ever named. In 1825 the English doctor Gideon Mantell described it from fossil teeth found in Sussex, which resembled enlarged iguana teeth; the story is told in Iguanodon: Gideon Mantell and the Sussex teeth. For half a century, however, it was known only from scattered bones.

With so little to go on, early reconstructions relied heavily on guesswork. Mantell placed a conical spike on the animal’s nose, and the life-size models of the 1850s at Sydenham, the Crystal Palace Dinosaurs, showed Iguanodon as a heavy, rhinoceros-like quadruped. Nobody had yet seen a complete skeleton.

What happened in 1878

In 1878 miners at the Sainte-Barbe pit of the Bernissart colliery, near the French border, drove a gallery into an unusual mass of clay at a depth of about 322 metres. Inside it they came upon what they first took to be fossilised wood. The pieces turned out to be bone, and soon whole skeletons were emerging.

The mining company informed the Royal Museum of Natural History in Brussels, headed by Édouard Dupont. The museum sent Louis De Pauw, its chief preparator, to direct the excavation. Work underground continued from 1878 to 1881 in hot, cramped conditions, with the threat of firedamp (explosive mine gas) and flooding always present.

De Pauw developed methods that became standard in palaeontology. Each skeleton was divided into blocks, recorded on detailed plans and drawings, and coated in plaster to hold the fragile bone together. Around 600 blocks are commonly cited as having been brought to the surface and transported to Brussels, a total of roughly 130 tonnes of rock and fossil.

Why so many in one place

Geologists working at the mine soon realised that the bones lay in clay that had filled a deep natural sinkhole, cut down into the much older Carboniferous coal beds. During the Early Cretaceous, around 125 million years ago, this depression held a lake or swampy basin. Dead animals were washed in and buried in fine sediment over a long period.

The skeletons were found at several different levels, which suggests they did not all die at once. Older ideas of a single herd falling into a ravine have given way to the view that carcasses accumulated in the basin over repeated events, possibly floods.

Louis Dollo and the reconstruction

The Belgian-born zoologist George Albert Boulenger named the new species Iguanodon bernissartensis in 1881. The main scientific study, however, fell to Louis Dollo, a young French-born engineer and naturalist who joined the Brussels museum in 1882. He spent much of his career on the Bernissart material, publishing a long series of papers.

Dollo and De Pauw mounted the first complete skeleton in 1883, inside the former chapel of the Nassau palace in Brussels, a space large enough for the work. They used ropes and scaffolding to position the bones, guided by the skeletons of birds and kangaroos. The result showed Iguanodon standing upright on its hind legs, with the tail resting on the ground like a tripod.

The most famous correction concerned the spike. The complete skeletons showed that Mantell’s “nose horn” was really a conical thumb spike, one on each hand. This single finding transformed how people imagined Iguanodon.

Later research and conservation

The upright, kangaroo-like pose became the standard image of Iguanodon for nearly a century and was copied in books and museums worldwide. In about 1980 the British palaeontologist David Norman restudied the Bernissart skeletons in detail. He concluded that adults mostly walked on all fours, held the tail roughly horizontal, and that Dollo had had to break the tails of some mounts to bend them down to the ground.

The bones also suffered from “pyrite disease”, in which iron sulphide minerals in the fossils react with moist air and slowly crumble the bone. The skeletons have been treated several times, notably in the 1930s and again during a major renovation of the gallery in the 2000s, to slow the damage.

Mining at the Sainte-Barbe pit ended without the deposit being exhausted. In 2002 and 2003 scientists drilled boreholes at Bernissart and recovered bone fragments at depth, confirming that more fossils remain underground.

Key people

Louis De Pauw was the museum preparator who led the work underground. His careful mapping of each skeleton before removal means that, well over a century later, researchers can still reconstruct how the bones lay in the mine.

Louis Dollo (1857–1931) devoted decades to the Bernissart animals. Beyond the reconstruction itself, he is remembered for “Dollo’s law”, the idea that evolution does not exactly retrace its steps, and for pioneering the study of fossils as living animals adapted to their environments, an approach he called ethological palaeontology.

Édouard Dupont (1841–1911), director of the Brussels museum, secured the government support and funding that made the long and costly excavation possible. George Albert Boulenger (1858–1937), later a noted zoologist at the British Museum, gave the main species its scientific name.

The miners and engineers of the Bernissart colliery also deserve credit. They recognised that the strange material was important, stopped work in the gallery and alerted scientists rather than treating the bones as waste rock.

Other finds and the site today

Bernissart produced far more than Iguanodon. The clays held fossil fish, turtles, amphibians, crocodile relatives including the small Bernissartia, insects and plants. A second, more lightly built iguanodontian found there is now often referred to a separate genus, Mantellisaurus, named in honour of Mantell.

The skeletons are today the centrepiece of the dinosaur gallery of the Royal Belgian Institute of Natural Sciences in Brussels, successor to the Royal Museum. Several stand upright in a large glass case, while others are shown lying in the positions in which they were found. A small museum in Bernissart itself displays an Iguanodon skeleton and tells the mining story.

By the numbers

Timeline

• 1825: Gideon Mantell names Iguanodon from teeth found in Sussex.
• 1854: The Crystal Palace models show Iguanodon as a horned quadruped.
• 1878: Miners in the Sainte-Barbe pit at Bernissart find bones about 322 metres underground.
• 1878–1881: Louis De Pauw directs the underground excavation for the Brussels museum.
• 1881: George Albert Boulenger names Iguanodon bernissartensis.
• 1882: Louis Dollo joins the museum and begins his study of the skeletons.
• 1883: The first complete skeleton is mounted in Brussels.
• c. 1980: David Norman’s restudy shows adults were mostly four-legged.
• 2002–2003: Boreholes at Bernissart confirm that more bones remain at depth.

Why it matters

Bernissart gave the world its first full view of a dinosaur skeleton, replacing guesswork with evidence. It established techniques of excavation, plaster jacketing and mounting that palaeontologists still use. And the many complete individuals from one site have allowed scientists to study growth, variation and posture in a way few other dinosaur finds permit.