Since their discovery in the Bernissart coalmine, the Iguanodon skeletons have gone through 130 rather turbulent years. This unique collection is kept at the Royal Belgian Institute of Natural Sciences (IRSNB). The various physical and chemical conservation techniques implemented haven't prevented their deterioration. In his doctoral thesis on mineralogical sciences, which he defended at the University of Liège, Thierry Leduc, a technical expert at IRSNB, carried out detailed mineralogical analyses, allowing him to understand the mechanisms brought into play during bone fossilisation on the one hand, and the causes of this deterioration on the other hand. His work has helped to identify some 30 different minerals in the Iguanodon bones. Some of these minerals formed during fossilisation, the main one being pyrite, which is partly responsible for the bones’ fragility. Others formed after their excavation. Despite preservation treatments, contact with the ambient air and humidity has led to the alteration of the pyrite and the formation of 16 different secondary minerals, including gypsum. Among other things, the growth of gypsum crystals is responsible for the appearance of cracks in the bones.

It was in March 1878 that miners in the Bernissart coalmine, who were working on a coal seam at a depth of 322 m, came across a vast pocket of clay. Such geological faults were already well known at the time and were referred to as ‘crans’ (sinkholes). The miners therefore dug a search gallery through this sinkhole in order to find the coal seam on the other side. It was then that they discovered the dark, crumbly objects they initially believed to be pieces of wood filled with gold, owing to the large amount of pyrite crystals within them. However, the colliery’s doctor showed that they were actually dealing with bones, not wood. The colliery’s engineers sent the bones to several specialists and P-J Van Beneden, a professor at the University of Louvain, quickly identified these fossils as belonging to the Iguanodon genus of dinosaur. This genus was discovered for the first time in England in 1825 and the species was named Iguanodon mantelli by H. Von Meyer, a German palaeontologist, because the animal’s teeth resembled those of the modern-day iguana (Iguanodon in Greek means ‘iguana tooth’), even though we now know that Iguanodons are not related to iguanas but dinosaurs.

The Bernissart site is invaluable owing to the wealth of fossils excavated there during the three years of excavations that followed their discovery. Some 30 complete, articulated Iguanodon skeletons were extracted from the depths of Bernissart, as well as two crocodiles, one insect fragment, dozens of coprolites and thousands of plant fragments. These fossils had been lying in the black clay known as ‘Wealdian clay’ for a very long time, dating from the Lower Cretaceous (140-120 million years). All the Iguanodon skeletons discovered belong to the Iguanodon berissartenis species, except for one smaller one: Iguanodon atherfieldensis. Since then, Iguanodon bernissartensis has been discovered throughout Europe, Asia, South American and North Africa.