Glowing spider fossils prompt breakthrough study of how they were
preserved at Aix-en-Provence

Date:
April 21, 2022
Source:
University of Kansas
Summary:
A new study asks: What are the unique chemical and geological
processes at Aix-en-Provence that preserve spiders from the
Oligocene Period so exquisitely?


FULL STORY ==========================================================================
A geologic formation near Aix-en-Provence, France, is famed as one of
the world's chief treasure troves of fossil species from the Cenozoic
Era. Since the late 1700s, scientists there have been unearthing amazingly well-preserved fossilized plants and animals.


==========================================================================
The Aix-en-Provence formation is particularly known for its fossilized terrestrial arthropods from the Oligocene Period (between roughly 23-34
million years ago). Because arthropods -- animals with exoskeletons like spiders -- are rarely fossilized, their abundance at Aix-en-Provence
is remarkable.

A new study in the journal Communications Earth & Environmentfrom
researchers at the University of Kansas is the first to ask: What are
the unique chemical and geological processes at Aix-en-Provence that
preserve spiders from the Oligocene Period so exquisitely? "Most life
doesn't become a fossil," said lead author Alison Olcott, 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 to have hard parts like bones, horns and teeth. So, our record
of soft-body life and terrestrial life, like spiders, is spotty -- but
we have these periods of exceptional preservation when all circumstances
were harmonious for preservation to happen." Olcott and her KU co-authors Matthew Downen -- then a doctoral candidate in the Department of Geology
and now the assistant director at Center for Undergraduate Research --
and Paul Selden, KU distinguished professor emeritus, along with James Schiffbauer of the University of Missouri, sought to discover the exact processes at Aix-en-Provence that provided a pathway for preservation
for the spider fossils.

"Matt was working on describing these fossils, and we decided -- more
or less on a whim -- to stick them under the fluorescent microscope
to see what happened," Olcott said. "To our surprise they glowed,
and so we got 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 exploring the chemistry and discovered the fossils
themselves contain a black polymer made of carbon and sulfur that, under
the microscope, looks like the tar you see on the road. We also noticed
there were just thousands and thousands and thousands of microalgae all
around the fossils and coating the fossils themselves." Olcott and her colleagues hypothesize that the extracellular substance these microalgae, called diatoms, are known to produce would have protected the spiders
from oxygen and promoted sulfurization of the spiders, a chemical change
that would explain preservation of the fossils as carbonaceous films
over the millions of ensuing years.



========================================================================== "These microalgae make the sticky, viscous gloop -- that's how they
stick together," the KU researcher said. "I hypothesized the chemistry
of those microalgae, and the stuff they were extruding, actually made it possible for this chemical reaction to preserve the spiders. Basically,
the chemistry of the microalgae and the chemistry of the spiders
work together to have this unique preservation happen." Indeed, this sulfurization phenomenon is the same as a common industrial treatment
used to preserve rubber.

"Vulcanization is a naturally occurring 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, which
is why we do it to rubber to make it last longer. What I think happened
here chemically is the spider exoskeleton is chitin, which is composed
of long polymers with carbon units near each other, and it's a perfect environment to have the sulfur bridges come in and really stabilize
things." Olcott said the presence of diatomic mats may potentially act
as a guide to find more deposits of well-preserved fossils in the future
"The next step is expanding these techniques to other deposits to see
if preservation is tied to diatom mats," she said. "Of all the other exceptional fossil preservation sites in the world in the Cenozoic Era, something like 80 percent of them are found in association with these microalgae. So, we're wondering if this explains most of these fossil
sites that we have in this time -- basically from soon after the dinosaurs
went extinct until now. This mechanism could be responsible for giving
us information to explore the evolution of insects and other terrestrial
life post-dinosaurs and to understand climate change, because there's a
period of rapid climate change and these terrestrial organisms help us understand what happened to life last time climate started shifting."
Olcott and her colleagues are the first to parse the chemistry of
preservation at Aix-en-Provence, a fact she chalks up in part to
challenges of carrying out science during COVID-19 restrictions.

"I honestly think this study is partially a result of pandemic science,"
she said. "The first batch of these images showed up in May 2020. My
lab was still closed; I was two months into my leg of 18 months at
home with kids all the time -- and so I had to change how I was doing
science. I spent a lot of time with these images and these chemical maps
and really sort 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."

========================================================================== Story Source: Materials provided by University_of_Kansas. Note: Content
may be edited for style and length.


========================================================================== Related Multimedia:
* Spider_fossils ========================================================================== Journal Reference:
1. Alison N. Olcott, Matthew R. Downen, James D. Schiffbauer, Paul A.

Selden. The exceptional preservation of Aix-en-Provence spider
fossils could have been facilitated by diatoms. Communications
Earth & Environment, 2022; 3 (1) DOI: 10.1038/s43247-022-00424-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220421131003.htm

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