(CNN) An international team of scientists say they have new insight into how the very earliest animals survived after traces of what they described as the world's oldest meal were found in a 550 million-year-old fossil.
Researchers from the Australian National University (ANU) analyzed ancient fossils from the Ediacaran period following their discovery in Russia in 2018. The findings were published in the journal Current Biology this week.
Some of the oldest life on Earth is referred to as the Ediacaran biota. This group is based on the earliest fossils ever discovered, providing evidence of complex, multicellular organisms.
In a fossilized specimen of the slug-like Kimberella, the team detected molecules of phytosterol preserved in the creature's gut. The chemical product, which is found in plants, suggested it ate algae and bacteria from the ocean floor.
Study co-author Jochen Brocks, a professor at the Australian National University, said the nutrient-rich algae may have contributed to Kimberella's growth.
"The energy-rich food may explain why the organisms of the Ediacara biota were so large. Nearly all fossils that came before the Ediacaran biota were single-celled and microscopic in size," Brocks said, according to a press release.
The palaeontologists suggested that Kimberella was likely one of the most advanced creatures of the Ediacaran era with a mouth and a gut and digested food the same way modern animals do.
"Scientists already knew Kimberella left feeding marks by scraping off algae covering the sea floor, which suggested the animal had a gut," Brocks explained. "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," he said in the news release.
Another organism called Dickinsonia, one of Earth's earliest animals, was a less advanced creature, without a mouth or gut. It grew up to 1.4 meters [4'5 feet] in length and had a rib-like design imprinted on its body, according to the researchers.
The Kimberella and Dickinsonia fossils were collected from cliffs near the White Sea in Russia's north-west in 2018, by the study's lead author, Dr. Ilya Bobrovskiy of the GFZ German Research Center for Geosciences. He completed the work as part of his doctoral thesis at ANU.
Dr. Bobrovskiy said the findings are helping scientists track the evolution of the earliest animals, and how they relate to their descendants today.
He described the animals of the Ediacaran biota, which lived on Earth prior to the 'Cambrian Explosion' that led to the modern animal, as "the origin of us and all animals that exist today."
" [They ] 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," he explained in the news release.
"These creatures are our deepest visible roots," he added.