This is the fifth post on my Brussels trip. The first can be found here.
For this post I decided to share the story behind the centrepiece of the Royal Belgian Institute of Natural Sciences (or Museum of Natural Sciences). Like many young boys, I became enthralled by dinosaurs as a kid. Gigantic, ferocious lizards? What’s not to like? So I couldn’t pass up the opportunity of seeing Europe’s largest dinosaur collection. The museum’s most prized exhibit is one of the world’s best group displays of dinosaurs: the Bernissart Iguanodons.
Iguanodons were first discovered in England in 1825, making them one of the earliest known dinosaurs. The name Iguanodon is owed to their teeth, which resemble those of modern-day iguanas (‘don’ means tooth in Greek). This made Iguanodon only the second dinosaur to be named (after Megalosaurus). Today there are seven recognised species of these large herbivores. They existed through the late Jurassic to the late Cretaceous (161-65 million years ago).
The museum’s Iguanodons were discovered by miners in the town of Bernissart in 1878. While digging for coal, the miners encountered a vast pocket of clay. These geological features, known as ‘crans’, are ancient sinkholes. The miners began digging through the sinkhole to reach the coal seam on the other side. As they made their way through they encountered dark, crumbly objects which they initially took for wood. The colliery’s doctor, however, recognised them as bones. They were soon identified as Iguanodon remains belonging to the Lower Cretaceous (140-120 million years).
During the Lower Cretaceous Bernissart was most likely a marshy valley surrounded by conifer-covered hills. The valley contained enormous ferns (likely the Iguanodons main food source). The climate was hot and humid and alternated between dry and rainy seasons. Sharing the landscape with the Iguanodons were numerous crocodiles, turtles, salamander-like amphibians, insects and fish. A small number of mammals also existed at that time, but were most likely only small, shrew-like insectivores that hunted at night to avoid becoming the food of the mighty dinosaurs.
Sinkholes are natural shafts that occur when soluble rock deep underground dissolves, in this case due to underground water. This causes the higher rocks to collapse. At Bernissart, the surface sand and clay was gradually drawn into the shaft creating a marsh on the surface. Sometime later the hapless Iguanodon got trapped in the marsh. This happened in a single event meaning the individuals likely belonged to a single herd. There were thirty-eight individuals in total, the largest Iguanodon discovery ever.
As the sand and clay was slowly sucked into the sinkhole the corpses were carried with it, taking them 321 metres below ground. Eventually the shaft filled and became covered over by other types of soil.
The Bernissart site was excavated over a period of three years under the supervision of palaeontologist Louis Dollo. Afterwards he began studying the fossils to determine their original form.
There was initially a great deal of confusion about Iguanodon’s shape, posture and movement. An early reconstruction even had the creature perched on a tree branch. This seems a little overly optimistic as we now know that they would have weighed around three tonnes.
The idea of Iguanodon being a lightweight, tree-dwelling creature was first challenged by the eminent scientist Sir Richard Owen. He argued that Iguanodon were heavy creatures with a crocodile-like head and a body similar to an elephant or rhinoceros (although scaly). He also argued that they walked on all fours using their short, heavy legs with big claws. This posture was challenged by another palaeontologist, Joseph Leidy, who believed the front limbs were too short for quadrupedal motion. The later discovery of the Bernissart fossils strongly supported Leidy’s case. The exceptionally well-preserved specimens clearly showed that Iguanodon had powerful hind legs, allowing it to stand upright, and use its arms for grasping food.
But Dollo’s work on the fossils didn’t just answer old questions. It also created new ones. During his reconstruction he used a kangaroo for reference. But he used it for a little more than just reference. It was later shown that Dollo had actually broken the tail bones to allow the skeleton to sit upright. Clearly, he tried to model the dinosaur’s posture on a kangaroo. We now know that Iguanodon tails couldn’t have flexed in this way. The confusion he created dominated for over a century.
It’s still debated whether they walked on all fours, the general view is that there were quadrupeds for walking and running and would have stood on their hind legs for grazing or defence.
This particular species of Iguanodon was dubbed Iguanodon bernissartensis, after the discovery. They’ve since been found throughout Europe, Asia, South American and North Africa (at the time the continents were connected together in a super-continent called Pangea).
It was fascinating to take a look at the remains. I’d never seen such a large collection of one species before. The museum had even recreated the scene chanced upon by the miners. In the basement they’d recreated the fossil collection as they were in the mineshaft: twisted and in disarray with the disaster befallen their herd frozen in time for us to discover.