Oldest evidence of digested plants in a roughly 575-million-year-old creature’s gut

The remains of an ancient meal are helping scientists learn about the planet's oldest large animals.
Kimberella fossil
A Kimberella fossil. Dr, Ilya Bobrovskiy/GFZ-Potsdam

Millions of years before Americans started celebrating Thanksgiving, Ediacara biota were munching on the bacteria and algae along the ocean floor.

The world’s oldest large organisms, Ediacara biota are a family of animals that date back 575 million years ago. They even existed before the Cambrian explosion, a major expansion of animal life that happened approximately 541 million to 530 million years ago and changed the course of evolution for all life on Earth. They are extinct, and the fossil specimens recovered have been shaped like discs or plant fronds and some rare specimens are close to eight inches in diameter. From the fossils, it’s possible that they were similar to soft-bodied marine organisms like jellyfish.

Researchers from Australia recovered fossils of two Ediacara—Kimberella and Dickinsonia—in 2018 from steep cliffs in a remote area of Russia near the White Sea. Now, scientists are figuring out what these ancient creatures snacked on.

[Related: This 120-million-year-old bird may have been one of the first to shake its tail feathers.]

A new study published today in the journal Current Biology is revealing more about these strange and incredibly old bottom dwellers, including how they were able to consume and digest food. The team analyzed ancient fossils of the Kimberella that had a natural chemical product found in plants called phytosterol molecules preserved inside of them, which could have come from this animals’ last meal. Further examination of the molecular left overs confirmed that the slug-like Kimberella actually had a mouth, a gut, and even digested food the same way that present-day animals do.

“Our findings suggest that the animals of the Ediacara biota, which lived on Earth prior to the ‘Cambrian Explosion’ of modern animal life, were a mixed bag of outright weirdos, such as Dickinsonia, and more advanced animals like Kimberella that already had some physiological properties similar to humans and other present-day animals,” said lead author Ilya Bobrovskiy, who is now at GFZ-Potsdam in Germany, in a statement

Kimberella was likely one of the most advanced of all Ediacarans, but both creatures are part of the Ediacara biota family and have a structure and symmetry unlike anything living on Earth today. “Ediacara biota really are the oldest fossils large enough to be visible with your naked eyes, and they are the origin of us and all animals that exist today. These creatures are our deepest visible roots,” said Bobrovskiy

[Related: Who Were The First Organisms To Live On Land?]

The algae that they ate are rich in energy and nutrients and may have been key to Kimberella’s growth, according to the study. Nearly all fossils of organisms that pre-date Ediacara biota were single-celled and microscopic in size.

Using chemical analysis, the team was able to extract and analyze the sterol molecules contained in the fossil tissue. Cholesterol is important because it is one of the hallmarks that differentiates animals from plants and it’s how scientists found out that Ediacara biota are among the earliest known ancestors of all present-day animals. 

Scientists already knew that Kimberella left feeding marks by scraping the algae up off of the sea floor, which was a possible sign that it had a gut. When the team on this study analyzed the gut molecules, they were able to determine that Kimberella could determine exactly what it was eating and how to digest it. Additionally, Kimberella was so advanced that it even knew exactly which sterols were good for it and had fine-tuned gut to filter out all the rest. 

“This was a Eureka moment for us; by using preserved chemical in the fossils, we can now make gut contents of animals visible even if the gut has since long decayed,” said co-author Jochen Brocks, from the Australian National University Research School of Earth Sciences.

But, Dickinsonia, which Brooks deems even weirder than Kimberella, did not have a gut, which really shows how advanced Kimerella is.

So, as you gather around the table to give thanks on Thursday, say a quick thank you to Kimberella and all the other Ediacara, because without them, you might not be able to stuff your face with turkey, stuffing, and cranberry sauce.