In short:
Pristine trilobite fossils have been unexpectedly found preserved by volcanic ash in Morocco.
Palaeontologists previously thought fossils could not occur in volcanic rock.
What's next?
Palaeontologists want to explore volcanic sites in Australia in the hope of finding pristine fossils.
The palaeontology world has been flipped on its head after trilobite fossils dating back 509 million years were found perfectly preserved by volcanic ash in Morocco.
The discovery allows scientists to get their most detailed look yet at trilobites and their soft tissue structure.
University of New England palaeontologist and investigation co-lead, Professor John Paterson, said it went against everything he was taught.
"When you are being trained as a palaeontologists or a geologist you are told fossils only occur in sedimentary rocks, you'll never find them in volcanic rocks," he said.
"This [discovery] basically turns that on its head; we now have a new type of rock to look in for exceptionally preserved fossils."
The discovery was documented in a recent study published in the journal Science.
3D vision
Trilobites were an animal group including insects, crabs, and spiders that lived in the ocean between 252 and 521 million years ago.
The only known fossils consisted of hard body parts such as the exoskeleton.
Dr Paterson said the latest discovery also included the soft parts of the body.
"We have the antennae, the walking legs, we've even got the entire digestive system preserved in one of the specimens," he said.
"This is extraordinarily rare, and we are actually seeing everything in 3D because they've been preserved in this volcanic ash."
Pompeii preservation
Similar to remains found in Pompeii, the volcanic ash has preserved the fine details of the trilobites.
Dr Paterson said the violent nature of volcanic eruption could provide ideal conditions for fossil preservation.
"Such an event would have rapidly buried these trilobites that were living in shallow waters near the shoreline, with the volcanic ash quickly moulding and cementing these animals in place," he said.
"The ash is so fine-grained, it's a little bit like talcum powder, so it's very good at modelling all of the fine anatomical features right down to little bristles on the walking legs, which are about a tenth of a millimetre in length.
"It's absolutely amazing detail."
Bit of a mouth-full
The fossils have already led to new discoveries about trilobites' anatomy, particularly around the head.
Dr Paterson said by running a CT scanner over the fossils, researchers discovered a structure called the labrum, a fleshy lip attached to part of the head.
"That's where the mouth is located, and it acts like a feeding chamber where the food is processed," he said.
"Just behind this structure, you've got some very unusual feeding appendages, which I kind of describe as spiny spoons the trilobite would have used to chew its food and then scoop the food into its mouth.
"We have never seen anything like this before in trilobites."
New frontier
Dr Paterson said it was possible even larger animals, such as dinosaurs, could be found preserved in volcanic ash.
With Australia home to volcanic sites, he said it was possible some of the world's most preserved fossils could be found.
"Provided the conditions were right and you had the right volcanic activities present at the time, the sky is the limit in terms of the things we could find," Dr Paterson said.
"This has got me really excited to go back to some of the field sites I work on in South Australia where we do find some of these volcanic layers.
"No-one's really bothered to look in them for actual fossils, so I would love to go back and really focus my attention on those deposits."
Editor's Note 5/7/2024: This story has been amended to correct that the fossils are among some of the oldest known trilobite fossils, not the oldest definitively.