ABC Science /
By science reporter Belinda Smith
This 22-million-year-old spider glows in UV light, which helped palaeontologists piece together how it fossilised.(Supplied: Alison Olcott)
Gloopy goo that fatally snared spiders more than 22 million years ago may have also helped preserve them in exquisite detail.
Key points:
Soft-bodied animals such as spiders and insects tend to decay before they have a chance to fossilise
Gloopy goo that fatally snared spiders more than 22 million years ago may have also helped preserve them in exquisite detail.
Key points:
Soft-bodied animals such as spiders and insects tend to decay before they have a chance to fossilise
A palaeontological site in France is rich in soft-bodied animals, but the process of preservation has been a mystery
A new study of fossilised spiders suggests a sticky substance excreted by algae may have hardened the animals' exoskeleton
Researchers from the US and UK suspect sticky sulphurous secretions from algae hardened the brittle exoskeletons of the spiders and staved off decay, allowing them to fossilise.
The study, published today in Communications Earth & Environment, might also help direct palaeontologists to uncover more of these rare, delicate fossils, and get a better picture of ancient environments.
For Alison Olcott, a chemical palaeontologist at the University of Kansas and lead author of the study, the first hint that algae might be involved came when she and her colleague Matthew Downen discovered the fossils glowed.
In daylight, the spider fossils have a recognisable outline, but don't look too dissimilar from the rock they're embedded in.
But under a microscope that threw UV light on the fossils, the spiders lit up in crisp detail.
"All these amazing details, like little hairs … on the spiders were all of a sudden visible," Dr Olcott said.
"It was really exciting just how much more we could see, and we got very interested in what the chemistry of these fossils was that made them glow."
Study co-authors Alison Olcott (left) and Matthew Downen check out a glowing spider under the UV microscope.
(Supplied: Margaret Birmingham)
'A race against decay'
The spiders were originally found sandwiched between layers of sedimentary rock from Aix-en-Provence in the south of France, at a site discovered in the late 1700s.
Some 22.5 million years ago, the area hosted a lake or brackish lagoon, and it has yielded a wealth of fossils of organisms that lived in or near water, including insects, shrimp and, of course, spiders.
And it's these remains of softer, squishier animals that put Aix-en-Provence on the palaeontological map.
Amazing ancient arachnid in amberA tiny arachnid discovered in 100-million-year-old amber fills a critical gap between today's spiders and spider-like arachnids that lived before dinosaurs.
Spider exoskeletons — their crispy outer layer — decay much faster than, say, bones, shells and teeth, which are composed of hard, mineralised material.
"And with fossilisation, it's always a race against decay," Dr Olcott said.
But no-one had teased out exactly why the Aix-en-Provence site managed to preserve so many ancient soft-bodied animals so well.
To find out, Dr Olcott and her colleagues borrowed eight fossil spiders from the French National Museum of Natural History.
They made "elemental maps" showing the chemical make-up of different parts of the fossils.
Then they matched the chemical elements to different colours thrown off by the fossils when illuminated with UV light.
The dark brown remains of the spiders' abdomens glowed orange under UV light, and were made mostly of carbon and sulphur.
A chemical map reveals a coating rich in sulfur (yellow) on this spider fossil, plus two kinds of diatom in pink around it.(Supplied: Alison Olcott)
Carbon was expected. Spider exoskeletons are made from chitin, and chitin has lots of carbon, but no sulphur.
So where did the sulphur come from?
To fossilise a spider, just add sulphur
A clue to the sulphur source came from the thousands of tiny, needle-like fossils embedded in the rock surrounding the spiders.
These, the researchers suspected, were diatoms: single-celled algae that live in capsules made of glass.
Carbon was expected. Spider exoskeletons are made from chitin, and chitin has lots of carbon, but no sulphur.
So where did the sulphur come from?
To fossilise a spider, just add sulphur
A clue to the sulphur source came from the thousands of tiny, needle-like fossils embedded in the rock surrounding the spiders.
These, the researchers suspected, were diatoms: single-celled algae that live in capsules made of glass.
Excretions from diatoms, perhaps similar to these, could have stabilised spider chitin to the point it could fossilise.
(Getty Images: Alfred Pasieka/Science Photo Library)
Some diatoms exude gluey sulphur-rich substances, which help them clump together to create "diatom mats" that bloom on the water's surface.
So what Dr Olcott thought happened was an unfortunate spider wandered onto a diatom mat, got stuck, and was quickly encased by the sticky goo.
This formed a barrier that stopped oxygen from getting through to the corpse, and thwarted many microbes that would usually decompose it.
Sulphur in the diatom gloop also reacted with the chitin exoskeleton.
Chitin is made up of long chains that contain carbon. Should sulphur find its way in the mix, it links carbon atoms in neighbouring chitin chains.
This "bridging" would have bestowed extra strength to the chitin, Dr Olcott said.
"If this sulphurisation can happen on an hours-to-days scale, it really gives these soft-bodied organisms a fighting chance to be fossilised."
(Sulphur-bridging is commonly used today to harden rubbers, to make car tyres and the like, in the process known as vulcanisation.)
Eventually, the diatom mat sank to the bottom of the lake, where sediments covered the algae, along with the unfortunate creatures stuck on it.
And over the aeons, those sediments hardened and locked the fossils inside until they were brought to light once again in the 18th century.
Outside of Aix-en-Provence
Australian Museum and UNSW palaeontologist Matthew McCurry, who was not involved in the study, says the new research gets us closer to understanding what conditions are needed to fossilise more delicate species.
"The [fossil] record of spiders is really quite dismal across the whole world.
"They're small, fragile organisms, they don't turn into fossils very easily, so you need these really specific geochemical conditions to aid in their formation."
Some diatoms exude gluey sulphur-rich substances, which help them clump together to create "diatom mats" that bloom on the water's surface.
So what Dr Olcott thought happened was an unfortunate spider wandered onto a diatom mat, got stuck, and was quickly encased by the sticky goo.
This formed a barrier that stopped oxygen from getting through to the corpse, and thwarted many microbes that would usually decompose it.
Sulphur in the diatom gloop also reacted with the chitin exoskeleton.
Chitin is made up of long chains that contain carbon. Should sulphur find its way in the mix, it links carbon atoms in neighbouring chitin chains.
This "bridging" would have bestowed extra strength to the chitin, Dr Olcott said.
"If this sulphurisation can happen on an hours-to-days scale, it really gives these soft-bodied organisms a fighting chance to be fossilised."
(Sulphur-bridging is commonly used today to harden rubbers, to make car tyres and the like, in the process known as vulcanisation.)
Eventually, the diatom mat sank to the bottom of the lake, where sediments covered the algae, along with the unfortunate creatures stuck on it.
And over the aeons, those sediments hardened and locked the fossils inside until they were brought to light once again in the 18th century.
Outside of Aix-en-Provence
Australian Museum and UNSW palaeontologist Matthew McCurry, who was not involved in the study, says the new research gets us closer to understanding what conditions are needed to fossilise more delicate species.
"The [fossil] record of spiders is really quite dismal across the whole world.
"They're small, fragile organisms, they don't turn into fossils very easily, so you need these really specific geochemical conditions to aid in their formation."
NSW farmer's fossil discoveryWhen Nigel McGrath hit heavy rock while ploughing a field, little did he realise he was sowing the seeds of a discovery some 15 million years in the making.
Knowing how spiders could be preserved might help palaeontologists uncover more similarly fragile fossils by narrowing their search to fossilised diatom mats, called diatomites, Dr Olcott said.
"So rather than just looking through all the rocks [at a site], you might first see what's in the diatomites."
Dr McCurry was wary of extrapolating the results of the new study to sites elsewhere.
"The work they've done on the fossils from that one province is great — they've associated the [diatom] microfossils and the specific [fossilisation] pathway for those fossil spiders.
"But they haven't yet done any chemical analyses on fossils from around the world.
"And so that's really the next step — to take that hypothesis that they've put forward in this paper, and see if that really does hold true across the rest of the world."
Ancient Spider Reveals a Secret Glow That Sustained It For Eternity
Spider fossil under UV light.
Spider fossil under UV light.
(Olcott et al., Communications Earth and Environment, 2022)
NATURE
CARLY CASSELLA
21 APRIL 2022
A fossilized spider that glows under ultraviolet light has given away the secret of its exceptional 23-million-year-long existence.
When researchers placed the fossil and others like it under a fluorescent microscope on a whim, they were surprised to notice the subtle outline of the arachnids suddenly pop against their background.
"To our surprise they glowed, and so we got very interested in what the chemistry of these fossils was that made them glow," explains geologist Alison Olcott from the University of Kansas.
Analyses carried out using other forms of scanning technology, such as energy-dispersive X-ray spectroscopy, revealed most of the mineral making up the fossils and their surrounds contained silicon.
Yet the darker patches on the fossils contained large quantities of two other elements – carbon and sulfur.
Looking closer, scientists realized the spiders weren't alone. Buried alongside and on top of them were a bunch of other organisms never before seen in fossils of the Aix-en-Provence fossil assemblage in France.
"[T]here were just thousands and thousands and thousands of microalgae all around the fossils and coating the fossils themselves," Olcott says.
For centuries, scientists have been studying the insect and fish fossils found in this region of France, but only now are we beginning to understand how these fragile creatures were preserved for all that time.
Unlike shells, teeth, and bone, soft tissue rarely fossilizes. And when it does, it requires a unique set of circumstances.
If not for mats of microalgae, researchers think it's unlikely the fossilized spider from Aix-en-Provence would have made a lasting impression.
In the past, other scientists have argued that if soft tissue is buried alongside single-celled algae, like diatoms, it could protect the fragile material from the degrading effects of oxygen.
But this new finding suggests there's something other than oxygen shielding at play.
If diatoms produce enough of a sticky extracellular substance in their mats, it could react with organic polymers found in another organism's soft tissue.
This could trigger a chemical process known as sulfurization, which takes carbon units from the spider's exoskeleton and cross-links it with sulfur from the algae mats. The result ultimately stabilizes carbon and keeps it from degrading as quickly.
"These microalgae make the sticky, viscous gloop – that's how they stick together," explains Olcott.
"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."
The authors are still testing this hypothesis, but when they combed the literature on similarly aged fossils, they found the majority were exceptionally preserved in diatom-rich units.
The carbon-heavy chitin found in spider exoskeletons seems to interact particularly well with the microalgae's goo. While there are some carbon-rich areas outside of the spider fossil as well, these do not show carbon-sulfur complexes like those glowing yellow on the inside.
"The fact that these [carbon-sulfur] complexes are only found in association with the spider morphology indicates that it is likely that the spiders are the source of the organic material involved in sulfurization," the authors write.
NATURE
CARLY CASSELLA
21 APRIL 2022
A fossilized spider that glows under ultraviolet light has given away the secret of its exceptional 23-million-year-long existence.
When researchers placed the fossil and others like it under a fluorescent microscope on a whim, they were surprised to notice the subtle outline of the arachnids suddenly pop against their background.
"To our surprise they glowed, and so we got very interested in what the chemistry of these fossils was that made them glow," explains geologist Alison Olcott from the University of Kansas.
Analyses carried out using other forms of scanning technology, such as energy-dispersive X-ray spectroscopy, revealed most of the mineral making up the fossils and their surrounds contained silicon.
Yet the darker patches on the fossils contained large quantities of two other elements – carbon and sulfur.
Looking closer, scientists realized the spiders weren't alone. Buried alongside and on top of them were a bunch of other organisms never before seen in fossils of the Aix-en-Provence fossil assemblage in France.
"[T]here were just thousands and thousands and thousands of microalgae all around the fossils and coating the fossils themselves," Olcott says.
For centuries, scientists have been studying the insect and fish fossils found in this region of France, but only now are we beginning to understand how these fragile creatures were preserved for all that time.
Unlike shells, teeth, and bone, soft tissue rarely fossilizes. And when it does, it requires a unique set of circumstances.
If not for mats of microalgae, researchers think it's unlikely the fossilized spider from Aix-en-Provence would have made a lasting impression.
In the past, other scientists have argued that if soft tissue is buried alongside single-celled algae, like diatoms, it could protect the fragile material from the degrading effects of oxygen.
But this new finding suggests there's something other than oxygen shielding at play.
If diatoms produce enough of a sticky extracellular substance in their mats, it could react with organic polymers found in another organism's soft tissue.
This could trigger a chemical process known as sulfurization, which takes carbon units from the spider's exoskeleton and cross-links it with sulfur from the algae mats. The result ultimately stabilizes carbon and keeps it from degrading as quickly.
"These microalgae make the sticky, viscous gloop – that's how they stick together," explains Olcott.
"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."
The authors are still testing this hypothesis, but when they combed the literature on similarly aged fossils, they found the majority were exceptionally preserved in diatom-rich units.
The carbon-heavy chitin found in spider exoskeletons seems to interact particularly well with the microalgae's goo. While there are some carbon-rich areas outside of the spider fossil as well, these do not show carbon-sulfur complexes like those glowing yellow on the inside.
"The fact that these [carbon-sulfur] complexes are only found in association with the spider morphology indicates that it is likely that the spiders are the source of the organic material involved in sulfurization," the authors write.
(Olcott et al., Communications Earth and Environment, 2022)
Above: Electron image of fossilized spider abdomen overlain by chemical maps of sulfur (yellow) and silica (pink) in the magnified box.
Oftentimes when fossils like these are studied, they are only examined at a macroscopic scale, not a microscopic one, but the findings from this new research suggest that's an oversight.
In this instance, when the global pandemic stalled laboratory work, researchers used their time to examine the spider fossil at a microscopic level.
When they did, they found something entirely unexpected, something no one else had reported, despite all the centuries spent working on fossils from Aix-en-Provence.
In all likelihood, the discovery is relevant elsewhere, too.
"The next step is expanding these techniques to other deposits to see if preservation is tied to diatom mats," says Olcott.
"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."
We might have diatoms to thank for some of the most fragile fossils in our possession today.
The study was published in Communications Earth & Environment.
Above: Electron image of fossilized spider abdomen overlain by chemical maps of sulfur (yellow) and silica (pink) in the magnified box.
Oftentimes when fossils like these are studied, they are only examined at a macroscopic scale, not a microscopic one, but the findings from this new research suggest that's an oversight.
In this instance, when the global pandemic stalled laboratory work, researchers used their time to examine the spider fossil at a microscopic level.
When they did, they found something entirely unexpected, something no one else had reported, despite all the centuries spent working on fossils from Aix-en-Provence.
In all likelihood, the discovery is relevant elsewhere, too.
"The next step is expanding these techniques to other deposits to see if preservation is tied to diatom mats," says Olcott.
"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."
We might have diatoms to thank for some of the most fragile fossils in our possession today.
The study was published in Communications Earth & Environment.
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