A fossilized spider from the Aix-en-Provence Formation in France seen in a hand sample superimposed with a fluorescent micrograph of the same fossil. Under normal lighting, the spider fossil is difficult to distinguish from the surrounding rock matrix, but when the fossil is excited by ultraviolet light, its chemical makeup causes it to self-fluoresces brightly, revealing additional details of its preservation. Credit: Olcott et al.
Glowing spider fossils prompt a paranormal study of how they were preserved in Aix-en-Provence.
A geological formation near Aix-en-Provence, France, is famous as one of the world’s most important treasures of Cenozoic fossil species. Scientists have discovered exceptionally well-preserved fossilized plants and animals there since the late 18th century.
“Most of life does not become a fossil.” – Alison Olcott
The Aix-en-Provence Formation is particularly famous for fossilized terrestrial arthropods from the Oligocene period (~23-34 million years ago). Since arthropods – animals with exoskeletons like spiders – are rarely fossilized, their abundance in Aix-en-Provence is staggering.
A new study published in the journal Earth and Environment Communications On April 21, 2022, researchers at the University of Kansas are the first to ask: What unique chemical and geological processes in Aix-en-Provence keep spiders from the Oligocene period so remarkable?
“Most life does not turn into a fossil,” said lead author Alison Olcott, associate professor of geology and director of the University Research Center at Kuwait University. “It’s hard to become a fossil. You have to die under very specific conditions, and one of the easiest ways to become a fossil is to have hard parts like bones, horns, and teeth. So our record of soft-bodied life and terrestrial life, like spiders, is spotty — but we have preservation periods. exceptional when all conditions were harmonious for conservation to occur.”
Scanning of an electronic image of the abdomen of a fossilized spider reveals a black polymer on the fossil and the presence of two types of microalgae: a mat of upright diatoms on the fossils and centrioles dispersed in the surrounding matrix. This image is covered with chemical maps of sulfur (yellow) and silica (pink) revealing that while the microalgae is siliceous, the polymer covering the fossil is rich in sulfur. Credit: Olcott et al.
Olcott and her co-authors at KU, Matthew Downen—then a doctoral candidate in the Department of Geology and now associate director at the University Research Center—and Paul Selden, KU Distinguished Professor Emeritus, along with James Schiffbauer of the University of Missouri. To discover the exact processes in Aix-en-Provence that provided a pathway for the preservation of spider fossils.
“Matt was working on describing these fossils, and we decided – on a whim – to stick them under a fluorescent microscope to see what happened,” Olcott said. “To our surprise it glowed, and so we became very interested in what made it glow the chemistry of these fossils. If you look at the fossil on the rock, you’ll find that it’s almost indistinguishable from the rock itself, but it glows a different color under the fluorescent range. So, we set out to explore the chemistry and found out That the fossils themselves contain a black polymer made of carbon and sulfur that, under the microscope, is similar to the tar you see on the road. We also noticed there were thousands and thousands and thousands of microalgae all over the fossils and covering the fossils themselves.”
Spider fossil from Aix-en-Provence formation with white square indicating scanning electron microscope image location and chemical map of sulfur (yellow) and silica (pink) in upper left. Together, these reveal a black sulfur-rich polymer on the fossil and the presence of two types of siliceous microalgae: a mat of upright diatoms on the fossil and central diatoms dispersed in the surrounding matrix. Credit: Olcott et al.
Olcott and her colleagues hypothesize that the extracellular substance produced by these microalgae, called diatoms, could have shielded the spiders from oxygen and boosted their sulfur, a chemical change that would explain the preservation of the fossils as carbonaceous membranes over the following millions of years.
“These microalgae make a sticky, sticky ball – that’s how they stick together,” said the KU researcher. “I hypothesized that the chemistry of those microalgae, and the substances they emit, actually made it possible for this chemical reaction to preserve the spiders. Essentially, the chemistry of the microalgae and the chemistry of the spiders work together to get this unique conservation.”
In fact, this phenomenon of sulfur is the same common industrial processing used to preserve rubber.
“Vulcanization is a naturally occurring process — we do it ourselves to process the rubber in a known process,” Olcott said. “Sulfur takes the carbon and bonds it with the sulfur and fixes the carbon, which is why we do that with rubber to make it last longer. What I think happened here chemically is that the spider’s exoskeleton is chitin, which is long polymers with carbon units close together. And it’s a perfect environment for sulfur bridges to step in and really stabilize things.”
Olcott said the presence of diatomic mats would likely serve as evidence that more well-preserved fossil deposits will be found in the future.
“The next step is to extend these techniques to other deposits to see if conservation is associated with diatom mats,” she said. “Of all the other exceptional fossil preservation sites in the world in the Cenozoic era, approximately 80 percent are related to this microalgae. So, we wonder if this explains most of the fossil sites we have at this time – mainly after a while. Brief history of the extinction of the dinosaurs so far. This mechanism may be responsible for giving us information to explore the evolution of insects and other terrestrial life after the dinosaurs and to understand climate change, because there is a period of rapid climate change and these terrestrial organisms help us understand what happened to life last time the climate began shifting” .
Olcott and her colleagues were the first to analyze conservation chemistry in Aix-en-Provence, a fact they attribute in part to the challenges of applying science during COVID-19 restrictions.
“I honestly believe this study is partly the result of epidemiology,” she said. “The first batch of these pictures came out in May 2020. My lab was still shut down; I had been two months out of my 18 months at home with kids all the time – and so I had to change the way I did science. I spent a lot of time with these pictures. And these chemical maps and I’ve actually explored them in a way that probably wouldn’t have happened if all the labs were open and we could go in and do more conventional work.”
Reference: “Exceptional preservation of the fossils of the Aix-en-Provence spider could have been facilitated by diatoms” by Alison N. Olcott, Matthew R.; Earth and Environment Communications.
DOI: 10.1038 / s43247-022-00424-7
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