Glowing spider fossils lead to groundbreaking research into how they were preserved in Aix-en-Provence

Fossilized spider from the Aix-en-Provence Formation in France seen in hand sample overlaid with fluorescent microscopy image 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 UV lighting, its chemical composition causes it to brightly autofluorescent, revealing additional details of its conservation. Credit: Olcott et al

A geological formation near Aix-en-Provence, France, is known as one of the world’s most important treasures of fossil species from the Cenozoic era. Since the late 1700s, scientists have unearthed amazingly well-preserved fossilized plants and animals there.

The Aix-en-Provence Formation is best known for its fossilized terrestrial arthropods from the Oligocene period (between about 23-34 million years ago). Because arthropods — animals with exoskeletons like spiders — are rarely fossilized, their abundance in Aix-en-Provence is remarkable.

A new study in the journal Communication Earth & Environment of researchers at the University of Kansas is the first to ask: What are the unique chemical and geological processes in Aix-en-Provence that so exquisitely preserve Oligocene spiders?

“Most life doesn’t become a fossil,” said lead author Alison Olcott, an associate professor of geology and director of the Center for Undergraduate Research at KU. “It’s hard to become a fossil. You have to die under very specific circumstances, and one of the easiest ways to become a fossil is by having hard parts like bones, horns, and teeth. Life is, like spiders, spotty, but we have these periods of exceptional preservation where all the conditions were harmonious for preservation to take place.”

Olcott and her KU co-authors Matthew Downen — then a doctoral student in the Department of Geology and now the assistant director of the Center for Undergraduate Research — and KU Professor Emeritus Paul Selden, along with James Schiffbauer of the University of Missouri, sought to discover the exact processes in Aix-en-Provence that formed a pathway for the preservation of the spider fossils.

Glowing spider fossils lead to groundbreaking research into how they were preserved in Aix-en-Provence

Scanning electron image of fossilized spider abdomen reveals a black polymer on the fossil and the presence of two types of microalgae: a mat of straight diatoms on the fossil and scattered centric diatoms in the surrounding matrix. This image is overlaid by chemical maps of sulfur (yellow) and silica (pink) that reveal that while the microalgae are siliceous, the polymer covering the fossil is sulfur-rich. Credit: Olcott et al

“Matt was working on describing these fossils and we decided — more or less on a whim — to put them under the fluorescent microscope to see what happened,” Olcott said. “To our surprise, they glowed, and so we became very interested in what the chemistry of these fossils was that made them glow. If you just look at the fossil on the rock, they’re almost indistinguishable from the rock itself, but they glowed a different color under the fluorescent scope, so we started investigating the chemistry and found that the fossils themselves contained a black polymer made of carbon and sulfur that, under the microscope, resembles the tar you see on the road. also that there are just thousands and thousands and thousands of microalgae surrounding the fossils and covering the fossils themselves.”

Olcott and her colleagues hypothesize that the extracellular substance these microalgae, called diatoms, produce would have protected the spiders from oxygen and promoted the spiders’ sulfur formation, a chemical change that helped preserve the fossils as carbonaceous films over the millions. would explain. following years.

“These microalgae make the sticky, viscous gloop — that’s how they stick together,” said the KU researcher. “I hypothesized that the chemistry of those microalgae, and the stuff they extruded, actually allowed this chemical reaction to keep the spiders. Basically, the microalgae chemistry and the spider chemistry work together to create this unique preservation to happen.”

This sulfurization phenomenon is indeed the same as a conventional industrial treatment used to preserve rubber.

“Vulcanization is a natural process — we do it ourselves to cure rubber in a well-known process,” Olcott said. “Sulfurization takes carbon and cross-links it with sulfur and stabilizes the carbon, that’s why we’re doing it with rubber to make it last longer. What I think has happened chemically here is that the spider’s exoskeleton is chitin, which is compounded 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.”

Glowing spider fossils lead to groundbreaking research into how they were preserved in Aix-en-Provence

Spider fossil from the Aix-en-Provence formation with a white box indicating the location of the scanning electron microscopy image and the chemical map of sulfur (yellow) and silica (pink) top left. Together, these reveal a black sulfur-rich polymer on the fossil and the presence of two types of siliceous microalgae: a mat of straight diatoms on the fossil and scattered centric diatoms in the surrounding matrix. Credit: Olcott et al

Olcott said the presence of diatomic mats may serve as a guide to finding more deposits of well-preserved fossils in the future.

“The next step is to extend these techniques to other deposits to see if conservation is bound to diatom mats,” she said. “Of all the other exceptional sites for fossil preservation in the world in the Cenozoic, about 80 percent of it is found associated with these microalgae. So we wonder if this explains most of these fossil sites that we have in this mechanism.” could be responsible for giving us information to investigate the evolution of insects and other terrestrial life after dinosaurs and to understand climate change because there is a period of rapid climate change and these terrestrial organisms help us understand what is going on with life happened the last time the climate started to shift.”

Olcott and her colleagues are the first to dissect the chemistry of conservation in Aix-en-Provence, a fact she attributes in part to the challenges of conducting science during COVID-19 restrictions.

“I honestly think this study is partly the result of pandemic science,” she said. “The first batch of these images appeared in May 2020. My lab was still closed; I was home with kids all the time for two months in my leg of 18 months — so I had to change my way of doing science. spent a lot of time on these images and these chemical maps and kind of explored them in a way that they probably wouldn’t have happened if all the labs were open and we could have gone in and done more conventional work.”

Well-preserved fossils could be a result of past global climate change

More information:
Alison Olcott, The exceptional preservation of spider fossils from Aix-en-Provence could have been made possible by diatoms, Communication Earth & Environment (2022). DOI: 10.1038/s43247-022-00424-7.

Provided by the University of Kansas

Quote: Glowing spider fossils lead to groundbreaking research into how they were preserved in Aix-en-Provence (2022, April 21) retrieved Aug 24, 2022 from breakthrough -aix-en-provence.html

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