The Bernissart Iguanodons at a glance

Thirty relatively complete iguanodon skeletons were discovered 322m underground in a coal mine in Bernissart, Belgium at the end of the 19th century. Since the bones were still in their original position, it was possible to present the skeletons in ‘lifelike’ poses. They immediately attracted visitors from all over the world!

Today a 300m² glass case protects this national treasure and gives visitors an optimal view on each one of these gems. The eight Iguanodon bernissartensis specimens shown in the glass case vary greatly in size: they range from 629 to 730cm long and 390 to 506cm high! The sole Mantellisaurus atherfieldensis (former Iguanodon mantelli or Iguanodon atherfieldensis) specimen is much smaller: 391cm long and 362cm high.


In the basement you can also see the skeletons in the position they were found in in the mines and learn how they were discovered.




1878: The discovery of the Bernissart iguanodons

The story starts at the end of March 1878 at the Bernissart coal mine in Sainte-Barbe. Miners were digging at 322m when they came across a pocket of clay. Instead of going around it, they decided to go through. Several days later, they made a startling discovery: tree trunks filled with gold! What they had actually found were Iguanodon bones encrusted with pyrite (“fool’s gold”). On 12 April 1878, the Belgian Royal Museum of Natural History (as it was then known) was informed of the discovery by telegram.

12 April 1878 : The telegram to the museum that will get everything going. (Photo: RBINS)


Major discovery bones in fault Bernissart coal mine STOP Pyrite deterioration STOP Send Depauw to arrive Mons station tomorrow 8 AM STOP Will be there STOP Urgent STOP Gustave Arnaut.

Pyrite may shine like gold, but it is nothing more than iron sulphide (FeS2) and it is worthless. Hence its nickname, ‘Fool’s Gold’. The Bernissart iguanodon skeletons were completely filled with pyrite. When clay from the swamps covered the dinosaur corpses, they were decomposed by blue-green algae (cyanobacteria). The acid released reacted with the iron in the clay, thus forming pyrite. It gradually filled the many holes in the bones.

The word ‘pyrite’ is derived from the ancient Greek puritês lithos, meaning ‘fire stone’. Prehistoric men would use it to make fire, by striking pyrite against flint until there were sparks. The sparks caused a dry tinder fungus to glow, which set fire to dry twigs and grass.

Pyrite erupted from an iguanodon bone
Pyrite erupted from an iguanodon bone (Photo: RBINS)
The mineral pyrite
The mineral pyrite (Photo: RBINS)

The Cran of the Iguanodons: this was the name of the clay-filled pit containing the skeletons. Several galleries 322m deep were dug. At the entrance to the main one, two iguanodons were discovered in a vertical position with their skulls downwards. The other skeletons, more in the centre, were more or less horizontal.

As they were released they were divided into blocks. These – a total of almost 600! – were coated with plaster and taken to the surface in horse-drawn trucks.

Plan van de opgravingen in Bernissart (Foto: KBIN)
Ground plan of the Bernissart excavations (Photo: RBINS)

In the Museum laboratories


37 cartloads were required to carry the 130 tons of fossils, plaster and iron frames (to reinforce the largest blocks) to Brussels. The iguanodons were thoroughly cleaned in the Museum laboratories. The technicians removed the sediment in which they were covered and the pyrite they contained. They dipped them in a boiling hot bath of glue to solidify them, then covered them with tin foil to protect them from the damp.

Lavalette drawings


Starting from 1880, Gustave Lavalette and other artists from the "Royal Natural History Museum of Belgium" were commissioned to make detailed drawings of several iguanodons and one crocodile. They mainly showed them in the position in which they were discovered. To do so, they had to wait until the fossils were removed from the sediment and protective plaster. Fortunately, they were able to refer to the maps of the digs down in the mine.

During the excavations, the skeletons were divided into blocks of 0.5 – 2m (the contours are visible in this drawing). Each specimen received a letter and each block a number, and their exact positions were recorded. Once the fossils were moved to the Museum workshops, it was possible to carefully return them to their original positions. This depiction of an Iguanodon bernissartensis was drawn by Gustave Lavalette in 1883.

Iguanodon bernissartensis “lettre A”. Tekening: Gustave Lavalette, (RBINS1882-07-22)
Iguanodon bernissartensis “lettre A”. Drawing: Gustave Lavalette, (RBINS1882-07-22)
Iguanodon bernissartensis “lettre R”. Tekening: Gustave Lavalette, (RBINS1883-11-14)
Iguanodon bernissartensis “lettre R”. Drawing: Gustave Lavalette, (RBINS1883-11-14)
Nog een Iguanodon bernissartensis "Lettre L". Tekening: Gustave Lavalette (1883).
Iguanodon bernissartensis "lettre L". Drawing: Gustave Lavalette (1883).
“Iguanodon mantelli”. Tekening: Gustave Lavalette, (RBINS1883)
Mantellisaurus atherfieldensis. Drawing: Gustave Lavalette, (RBINS1883)

In 1882 the Iguanodons were assembled with a biped posture


Louis Dollo, who supervised this very first assembly, was convinced that the Iguanodon bernissartensis was a biped. He argued that the front and hind legs are not so different in quadrupeds. The spinal column is that of a biped. The hips and hind legs and the size of the head and chest are like those of ratites (ostrich, cassowary…). Lastly, a fossil track discovered in England suggests that the Iguanodon moved about on its hind legs.

In 1882, under the direction of Louis Dollo, Louis De Pauw (the man with the beard, bended on one knee) began assembling the most complete specimens in their “probable life posture”.

Due to their size, a room with a high ceiling was required. They used the St George chapel (today part of the Royal Library). Here, they built a scaffold hung with ropes.

The best position for each bone was obtained by adjusting the length of the ropes. Finally, once the skeletons would be assembled, they would be fitted with an iron frame to hold the bones in place.

Een jonge Louis Dollo. (Foto: KBIN)
A young Louis Dollo. (Photo: RBINS)

The Iguanodons on display

The very first specimen to be assembled was the Iguanodon bernissartensis. It was put on display in the inner courtyard of the former Palace of Nassau in 1883. It was kept in a glass case to protect it from the bad weather. It was soon joined by a second specimen, a tiny Iguanodon mantelli (now known as Mantellisaurus atherfieldensis), and various animal and vegetable fossils that were also found in the Bernissart mine.

Het allereerste opgestelde exemplaar, op de binnenplaats van het Hof van Nassau in Brussel.
The very first one displayed, in the courtyard of the Palace of Nassau in Brussels.

In the 1880s, the Palace of Nassau had become too small to exhibit the iguanodons. The "Museum" was thus transferred to a building in the Park Leopold: the “Convent”, to which they added the Janlet wing, which is where the iguanodons were kept from 1902 onwards. This photos (beneath) was taken during its construction in 1900, right about where today’s glass case begins. The iguanodons have been in the Janlet wing since 1902 but they were exposed to the air until 1932!

Due to the temperature and moisture variations, they slowly but surely began to crumble. This is why all the skeletons were dismantled between 1933 and 1937 and soaked in a protective mixture of alcohol and shellac.
Their brown colour is therefore not the result of being found in a coal mine.

1900 : A new museum wing for the Iguanodons
1900 : A new museum wing for the Iguanodons (Photo: RBINS)
1905: The Iguanodons on display without a glass cage.
1905: The Iguanodons on display without a glass cage. (Photo: RBINS)

The iguanodon skeletons were dismantled once again in 1940: it was feared they might be damaged or even completely destroyed during the bombings.

They were kept in cellars whose openings were protected by sandbags. But those were so damp that the iguanodons had to be returned to the room before the end of the Second World War!


The Iguanodon posture was reviewed in 1980

Nearly a century after Louis Dollo, palaeontologist David B. Norman made a further investigation on the Iguanodon bernissartensis and reached very different conclusions: the spinal column was held in a somewhat horizontal position when the dinosaur walked or ran. Therefore, the "Kangaroo" posture on two legs was no longer relevant. However, the original skeletons mounted in this position remain as they are because they are too fragile to be changed.

Iguanodon walked on all fours.
Iguanodon walked on all fours. (Photo: RBINS)


Multifunctial hands


Multifunctional like a Swiss army knife
Multifunctional like a Swiss army knife (Photo: RBINS)

There are three completely different functions spread around the five digits of the iguanodon hand. This is quite remarkable, as there is nothing like such specialized hands in the rest of the animal kingdom!

The three central digits of the hand were used as a kind of hoof, to be walked upon and not to grasp with. They formed a structure that is remarkably similar to a three toed foot.

When looking at the hand in more details, it is quite clear that the central bones - the metacarpals - are tied together very tightly by ligaments, to form a weight-supporting structure.

The bones of the wrist are actually built like a series of brick layers, and the ligaments - the soft tissues that run around the wrist to protect the wrist bones - have actually ossified: they've turned from being soft tissue into strands of bone.

These form an incredibly powerful support for the weight transmitted via the hand, from the shoulders down to the toes.

The fifth toe comes out of the wrist region and forms an extra long, flexible, prehensile digit. That digit would be used for grasping (possibly vegetation).

Finally, here is the extraordinary thumb. This bone forms a large conical spike, coming out out from the wrist itself. It would be covered by a very sharp horny sheath.

That thumb would be a devastating weapon, especially during combat with predators that would try to prey on the iguanodon.

They may have been assembled and dismantled several times but the iguanodons are still standing in the same biped kangaroo position they were put in during the first assembly.

In hun glazen kooi. (Foto: KBIN)
In their glass cage. (Photo: RBINS)


Bernissart's other treasures

Apart from the dinosaurs in Bernissart, the digs unearthed thousands of fossils of animals and plants! They offer an insight into the type of climate and environment in which the iguanodons lived.

The Bernissart fish lived in fresh water. This Amiopsis dolloi resembles the contemporary Amia calva, a swamp fish found in the Everglades, in Florida (USA).

Chitracephalus (on right) protected its head by folding its neck sideways and Peltochelys (on left) by retracting it vertically. These turtles resemble contemporary species living in fresh water.

This tiny crocodile was discovered for the first time in Bernissart, hence its name: Bernissartia fagesii. Its back was covered with several rows of plates. The specimen on display is barely 66cm long.

Een van de vele fossiele vissen uit Bernissart: Amiopsis dolloi
Een van de vele fossiele vissen uit Bernissart: Amiopsis dolloi. (Foto: KBIN)
Turtles from Bernissart.
Turtles from Bernissart. (Photo: RBINS)
The small crocodile Bernissartia fagesii.
The small crocodile Bernissartia fagesii. (Photo: RBINS)

The nearly two-metre-long Anteophtalmosuchus hooleyi (formerly: Goniopholis simus) was the largest crocodile from Bernissart. Its dorsal shield, unlike that of Bernissartia fagesii, consists of only two rows of plates.

This cone (Pityostrobus bernissartensis) and this piece of glazed wood (Pinoxylon) are conifer fossils, also discovered in Bernissart.

Most of the fossil plants from Bernissart are from buckler ferns, Weichselia reticulata.
The herbivorous iguanodons probably ate a lot of them.

Anteophtalmosuchus hooleyi, de grote krokodil van Bernissart (Foto: E. De Bast & Th. Smith, KBIN)
Anteophtalmosuchus hooleyi, de grote krokodil van Bernissart (Foto: E. De Bast & Th. Smith, KBIN)
Fossilised conifers from Bernissart
Fossilised conifers from Bernissart (Photo: RBINS)
Weichselia reticulata
Weichselia reticulata (Photo: RBINS)

Bernissart was a hot, swampy region: several of its fossilized specimens lived only in hot climates (crocodiles, cicada etc.) and swamps (fish Amiopsis, ferns Weichselia etc.).

Bernissart, once a hot, marshy region
Bernissart, once a hot, marshy region (Drawing: RBINS)

Are there still any iguanodons in Bernissart?

Iguanodon skeletons can no longer be reached in Bernissart: the Cran of the Iguanodons is located in 300m deep and the mineshafts were filled in and sealed a long time ago! However, the Mining Engineering Department at Mons Polytechnic Faculty started drilling down to the Cran in 2002 and 2003. The aim was to delimit it more precisely and see if it still contained any iguanodons. The results? Some of the core samples taken in the depths of the Cran contain bone fragments: there are probably still some iguanodons deep under the ground!

The Saint-Barbara coal pit in Bernissart
The Saint-Barbara coal pit in Bernissart