New research has shone a light on how the world’s oldest large animals consumed and digested food. Animals from the Ediacaran period lived around 575 million years ago and by analyzing the chemicals in their fossilized guts, scientists were able to discover their diet. For a slug-like animal known as Kimberella, the team was able to work out that they must have had a mouth and a gut, and digested food just like modern animals do.
Kimberella and Calyptrina, a flat worm-like creature, shared a mixed diet of green algae and bacteria. Dickinsonia, another flat and striped critter from eons ago that could grow up to 1.4 meters (4.6 feet), did not have a mouth, so likely digested and absorbed food externally instead.
“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,” lead author Dr Ilya Bobrovskiy, from GFZ-Potsdam in Germany, said in a statement.
These fossils represent the oldest animals whose fossils are visible to the naked eye. They are the ancestors of all the animals that exist on Earth today. Molecular analysis of the fossils is how it was confirmed that these were animals back in 2018. Researchers found cholesterol, the hallmark of us and all other animals in the world.
Looking for other molecules, the team found other fat molecules that did not belong to the ancient animals. They were instead molecules belonging to bacteria and algae that must have been eaten as the last meal by this creature before it died and became fossilized.
“Scientists already knew Kimberella left feeding marks by scraping off algae covering the sea floor, which suggested the animal had a gut. 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,” added Professor Jochen Brocks, from Australian National University.
“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.”
The study was published in the journal Current Biology.