Bernissart Iguanodons’ Cause of Death to Be Re-Examined



Gustave Lavalette tekende alle iguanodons in de positie waarin ze werden gevonden in de mijn van Bernissart. (Foto: KBIN)
Bernissart Iguanodons’ Cause of Death to Be Re-Examined
post by
Reinout Verbeke

What killed approximately thirty iguanodons that were discovered at Bernissart: drought, drowning, marsh gas poisoning, or something else? A team of Belgian researchers are re-launching the investigation to try and find the prime suspect. Pascal Godefroit (RBINS) leads the project: “We’re going to re-examine old geological maps and core samples taken from the site in 2002, as well as looking into specimens that are yet to be studied.”

Since the discovery of the Bernissart iguanodons in 1878, their death has been the subject of much speculation. Louis Dollo, the celebrated palaeontologist, spent years studying the iguanodons and following the excavations. He thought the dinosaurs drowned or had been attacked by predators. In the sixties scientists thought that a drought or getting stuck in the mud was to blame. Did they jump or fall off a cliff like a researcher from the seventies believed? The eighties version of events was that they died of natural causes in the marsh, and then the bodies were slowly decomposed until a sinkhole formed, and the remains sank below the surface.

During the next four years, a team of researchers from the Royal Belgian Institute of Natural Sciences, Mons University and the Free University of Brussels will re-examine all the possible scenarios with the help of 3D scans of the fossils, geological maps of recently discovered excavation sites and information provided by two core samples that were removed in 2002 at the exact spot where the iguanodons were found. Scientists will also examine 3,000 fish fossils and analyse pollen and isotopes to find out if the environment changed drastically 125 million years ago.

A Collective Poisoning

During the initial conference in Mons at the beginning of June, Jean-Marc Baele, a geologist from Mons University, put forward some arguments in favour of a new hypothesis: a mysterious epidemic. “At a paleontological site where animals have died in a gradual and ‘passive’ way, about 80% of the remains are those of juveniles, because they were the weakest animals,” he explained. “It is remarkable that only adult specimens were found in the Bernissart mine. This could indicate a sudden, local, extinction.”

But who or what was this fast-acting assasin? Baele suspects hydrogen sulphide (H2S) of having been a so-called silent killer: “The iguanodons were found in layers of clay which contained a lot of mineral pyrite, iron disulphide (FeS2), which can be obtained from iron oxide (Fe2O3) and hydrogen sulphide, a gas that is toxic even in very low concentrations (a horse in Mont Saint-Michel died as a result of hydrogen-sulphide-producing seaweed). Did a geyser of sulphurous water (containing H2S) poison or choke a group of iguanodons 125 million years ago? The position in which the iguanodons were found, on their side with the head thrown back, indicates that this kind of poisoning was the culprit. The large number of fish fossils found in a separate layer, close to the iguanodons, might provide us with more clues…

3D Reconstruction

The discovery of the iguanodons was an important step for palaeontology. Pascal Godefroit states, “It was a Rosetta Stone for the palaeontologists of the time. More or less complete and still in their original positions, these fossils painted the first accurate picture of dinosaurs for scientists at the end of the 19th century. This iguanodon collection is the most beautiful in the world due to the quantity and the quality of the fossils. It is equally as good for studying their behaviour and their living and dying conditions, as it is for studying the ecology of the period.”

Major paleontological discoveries have always received a lot of interest. For more than 130 years, these centrepieces of the Museum have attracted visitors from Belgium and abroad. “That’s why we want the research to reach a wide audience via the internet or a documentary for example. We’re also thinking about creating a 3D reconstruction based on the original geological drawings and plans, which would allow an online exploration of the ‘crime scene’.”


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