Chemical analysis reveals the world's oldest meals

The contents of the last meals consumed by animals that inhabited Earth more than 550 million years ago have unearthed new clues about the physiology of our earliest animal ancestors, according to a new study led by The Australian National University (ANU).

Ediacara biota are the world’s oldest large organisms, dating back 575 million years, and were first discovered in the Ediacara Hills in South Australia’s Flinders Ranges. ANU researchers recently found that the animals ate bacteria and algae that was sourced from the ocean floor, revealing insights into how these strange creatures were able to consume and digest food. The team’s findings have been published in the journal Current Biology.

Fossils of Ediacara biota known as Kimberella and Dickinsonia were retrieved by lead author Dr Ilya Bobrovskiy, who completed the work as part of his PhD at ANU, from steep cliffs near the White Sea in Russia in 2018. Bobrovskiy noted, “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.”

The fossil tissue was found to contain preserved phytosterol molecules — a type of fat found in plants — that remained from the animals’ last meal, which the researchers were able to extract and analyse using advanced chemical analysis techniques. By examining the molecular remains of what the animals ate, the researchers confirmed that the slug-like Kimberella had a mouth and a gut and digested food the same way modern animals do, which likely makes it one of the most advanced Ediacarans.

The team also found that Dickinsonia, which grew up to 1.4 metres in length and had a rib-like design imprinted on its body, was less complex and had no eyes, mouth or gut. Instead, the odd creature absorbed food through its body as it traversed the ocean floor.

This Dickinsonia fossil depicts the animal’s distinctive rib-like design imprinted on its body. Image credit: Dr Ilya Bobrovskiy.

“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,” Bobrovskiy said.

Study co-author Professor Jochen Brocks added that algae are rich in energy and nutrients, and so may have been instrumental for Kimberella’s growth. He said, “The energy-rich food may explain why the organisms of the Ediacara biota were so large. Nearly all fossils that came before the Ediacara biota were single-celled and microscopic in size.”

Cholesterol is the hallmark of animals and was how, back in 2018, the ANU team was able to confirm that Ediacara biota are among our earliest known ancestors. The molecules contain tell-tale signatures that helped the researchers decipher what the animals ate in the lead-up to their death. The difficult part, said Brocks, was differentiating between the signatures of the fat molecules of the creatures themselves, the algal and bacterial remains in their guts and the decaying algal molecules from the ocean floor that were all entombed together in the fossils.

“Scientists already knew Kimberella left feeding marks by scraping off algae covering the sea floor, which suggested the animal had a gut,” he said. “But it was only after analysing the molecules of Kimberella’s gut that we were able to determine what exactly it was eating and how it digested food.

“Kimberella knew exactly which sterols were good for it and had an advanced 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. We then used this same technique on weirder fossils like Dickinsonia to figure out how it was feeding and discovered that Dickinsonia did not have a gut.”

Image caption: The ancient animal known as Kimberella. Image credit: Dr Ilya Bobrovskiy.

Please follow us and share on Twitter and Facebook. You can also subscribe for FREE to our weekly newsletters and bimonthly magazine.