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[EN VIDÉO] Interview: Where do you find dinosaur fossils? The dinosaurs disappeared 65 million years ago, but still left some traces in fossil form. But what are the most favorable geological conditions for their conservation and where can they be found? Futura-Sciences posed the question to Éric Buffetaut, paleontologist during this interview.
The Aix-en-Provence site, also known as “Eggs-en-Provence”, has been operated since 1700 and is full of fossils extraordinarily well preserved. dinosaurs of course, but not alone! Researchers at the University of Kansas studied spiders preserved in stone, which come from the‘Oligocenethe third period of theCenozoic era, between 23 and 34 million years ago. A rare phenomenon, because the fossilization is not spontaneous for this one arthropods on eight legs.
Living beings don’t normally freeze
Indeed, for the living, the most likely after death naturally remains decomposition, as explained by a study published in the journal Communication Earth & Environment Apr 21, 2022. “It’s hard to become a fossil”said Alison Olcott, lead author of the study and associate professor of geology at the University of Kansas. You have to die under very specific circumstances, and one of the easiest ways to become a fossil is to have hard parts, such as bones, horns, and teeth. So our account of the soft body life and the terrestrial life, such as: spidersis unequal, but we have those periods of exceptional preservation where all the conditions were harmonious for preservation to take place.
Microalgae as preservatives
To determine exactly the conditions that enabled spider conservation, the team looked for every aspect of the fossils they found. Here they found the conservative element: the diatomsmicroalgae present in all aquatic environments. “We have decided to put them under the microscope fluorescence to see what happened. To our surprise they glowed, so we were very interested in the chemistry of these fossils that make them shine, explained A. Olcott. So we started researching chemistry and found that the fossils themselves are a polymer black composed of carbon and from sulfur which, under the microscope, looks like the tar you see on the road. We also noticed that there were just thousands and thousands and thousands of microalgae surrounding the fossils, covering the fossils themselves.”†
The diatoms would thus have deposited on the spiders, and their siliceous external structure would then have protected them from interactions with the surrounding oxygen, preventing their decomposition. They would also have preferred the sulphurisationa chemical transformation that consists of introducing an ion sulphide in a carbon structure: hence the observation of the black polymer composed of carbon and sulfur. This polymer, which is particularly stable, was then preserved intact for millions of years before being found in Aix-en-Provence. “What happened here chemically, I think, is that the…exoskeleton of the spider is of the chitinwhich is made up of long polymers with carbon units close together, and it’s a perfect environment for the disulfide bridges to come in and really stabilize things,” detailed A.Olcott.
An explanation for a multitude of fossils
But the process revealed by the researchers wouldn’t just apply to these fossils from the south of France. On the contrary, Alison Olcott and her team believe that the presence of this microscopic algae could explain a large number of preserved fossils. “The next step is to extend these techniques to other deposits to see if conservation is related to diatoms.she said. Of all the other prime fossil conservation sites in the world in the era cenozoicabout 80% of them are found associated with these microalgae”.
Global mapping of locations where researchers have reported the presence of diatoms (diamonds if yes, circle if not). The color distinguishes the type of environment (marine, non-marine, transition zone) © Olcott et al
More than these particular spider fossils, all terrestrial organisms dating to shortly after the extinction of the dinosaurs may have been preserved by this method. The team then plans to investigate the relationship between the evolution of biodiversity and the climate changes† “This mechanism could allow us to track the evolution of insects and other post-dinosaur terrestrial organisms and especially to understand climate change; because there is currently a period of rapid climate change and these terrestrial organisms are helping us understand what happened to life the last time the climate changed. † concluded A. Olcott.
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