The oldest animals appear in the fossil record among Ediacaran biota communities. In new research, paleontologists from the Australian National University and elsewhere examined the gut contents of three Ediacaran species — the 558-million-year-old tube worm-like Calyptrina and the mollusk-like Kimberella as well as one of the key Ediacaran animals, Dickinsonia — using biomarker molecules. Their results show that Calyptrina and Kimberella possessed a gut and shared a diet of green algae and bacteria, while Dickinsonia had a different feeding mode and possible external digestion.
An artist’s impression of Kimberella. Image credit: Oleg Kuznetsov, 3Depix.
Calyptrina, Kimberella and Dickinsonia are part of the Ediacaran biota that lived on Earth about 20 million years prior to the Cambrian Explosion, a major event that forever changed the course of evolution of all life on Earth.
These ancient creatures has a structure and symmetry unlike anything that exists today.
“Ediacaran 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 Dr. Ilya Bobrovskiy, a researcher at GFZ-Potsdam.
“Our findings suggest that the animals of the Ediacaran biota 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.”
In the study, Dr. Bobrovskiy and his colleagues analyzed Ediacaran macrofossils containing preserved phytosterol molecules — natural chemical products found in plants.
By examining the molecular remains of what the animals ate, the researchers found that both Calyptrina and Kimberella had a gut and digested food the same way modern animals do.
They also found that Dickinsonia was less complex and had no eyes, mouth or gut. Instead, it absorbed food through its body as it traversed the ocean floor.
“The energy-rich food may explain why the organisms of the Ediacaran biota were so large. Nearly all fossils that came before the Ediacaran biota were single-celled and microscopic in size,” said Australian National University’s Professor Jochen Brocks.
Using advanced chemical analysis techniques, the authors were able to extract and analyze the sterol molecules contained in the fossil tissues.
The molecules contained tell-tale signatures that helped them decipher what the animals ate.
Their results reveal that Calyptrina and Kimberella shared a diet of green algae and bacteria.
“The difficult part 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,” Professor Brocks said.
“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 analyzing 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.”
The results appear in the journal Current Biology.
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Ilya Bobrovskiy et al. Guts, gut contents, and feeding strategies of Ediacaran animals. Current Biology, published online November 22, 2022; doi: 10.1016/j.cub.2022.10.051
