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Fossil of the mollusk Kimberella
Photo: Dr Ilya Bobrovskiy / GFZ Potsdam
Living beings ate something and digested it with the help of an intestine more than 550 million years ago.
The oldest documented meal consisted of bacteria and algae, researchers report in the journal Current Biology.
The creatures belonged to the so-called Ediacaran fauna, which was widespread on sea floors.
For the first time members of the diverse group were found in Australia.
The samples now being examined come from a cliff in north-west Russia on the White Sea.
The Ediacara representatives are "really the oldest fossils large enough to be visible to the naked eye, and they are the origin of us and all animals that currently exist," said first author Ilya Bobrovskiy from the German Research Center for Geosciences (GFZ) in Potsdam.
"These creatures are our deepest visible roots."
The team studied two members of the Ediacara, among others: the mollusk-like Kimberella and the tubeworm-like Calyptrina.
It was already known that Kimberella left grazing marks when she scraped algae from the seabed.
"But it was only after we analyzed the molecules of Kimberella's gut that we were able to determine exactly what she was eating and how she was digesting her food," said co-author Jochen Brocks of the Australian National University in Canberra.
eating without mouth
Experts determined the presence of various carbon ring compounds in the samples.
Because digestion in the intestine works chemically somewhat differently than other forms, the proportion of individual molecules in the samples revealed the type of metabolism.
In the samples, which contained Kimberella and Calyptrina, the researchers found evidence of algae and bacteria digested in a gut.
This was not the case in other animals examined.
According to the authors, another Ediacaran member named Dickinsonia was up to 1.4 meters long but had neither a mouth nor an intestine.
Instead, it ingested food as it moved across the sea floor through its body, which had a lamellar pattern on the surface.
Dickinsonia also left traces that can still be found today.
The study suggests that Ediacarans were "a mix of downright oddballs like Dickinsonia and more advanced animals like Kimberella, which already had some physiological characteristics similar to humans and other modern-day animals," Bobrovskiy said.
The organisms lived just before the Cambrian Explosion, which began around 540 million years ago and produced a huge number of organisms.
Many animal tribes developed from which today's animal world is composed.
jme/dpa