Evrim Yazgin
Evrim Yazgin has a Bachelor of Science majoring in mathematical physics and a Master of Science in physics, both from the University of Melbourne.
Many of us can’t even remember what we had for breakfast. Meanwhile, scientists have confirmed that they have found the world’s oldest meal – in a fossil of an animal that lived 558 million years ago.
The results of the analysis are published in Current Biology. Corresponding author on the paper, Professor Jochen Brocks from the Australian National University (ANU), spoke with Cosmos about the discovery.
Brock first helps us imagine what we would see if we were to travel back in time to the Earth’s prehistory.
“Ediacara biota existed between 575 and 541 million years ago,” Brock says. “575 million years ago is when life got big. If you if you go further back in time, you’d need a microscope. You’d also need scuba gear and maybe even an oxygen mask on land. Everything is microorganisms, the biggest organisms would be a single-celled algae still tenths to hundredths of millimetre in size. In shallow water, you would probably see that the sea floor was covered with the green microbial mat.”
“When we go back in our time machine to the Ediacara hills 575 million years ago, you start actually seeing something lying on these mats or sticking out of the mats. And these are the Ediacarans.
“These big creatures emerged 575 million years ago out of absolutely nowhere.”
Read more: Fossils from half a billion years ago preserve first skeletons, solving centuries-old mystery
Brock also explains that Ediacarans were unlike anything we see today or even in any other stage in the fossil record. While almost all animals today are bilaterally symmetrical (like humans) or pentaradially symmetrical (like sea stars), Ediacarans had all kinds of symmetries that have not survived in modern animals.
Many Ediacarans, particularly earlier on in the geological timeline, escape categorisation. Are they animals? Are they plants? Are they proto-animals? Are they something completely different? No one really knows.
Brock says these “extremely unusual weirdos” probably lived in deep water. The Ediacara found in South Australia’s Flinders Ranges are sometimes called the “White Sea biota” as they are also found in Russia’s White Sea.
Brock explains that the Current Biology paper’s first author, Dr Ilya Bobrovskiy, who completed his PhD at ANU before going to GFZ-Potsdam in Germany, came to him with a “crazy idea.”
One of the most famous Ediacarans is Dickinsonia. Brock recounts that Bobrovskiy had found Dickinsonia fossils “preserved in a way they are not preserved anywhere in the world. The sediments there are so fresh and so well preserved, you can take the ancient sea floor and almost mould in your hands to make pottery. It had not even solidified yet.”
Bobrovskiy told Brock: “The fossils are sandwiched between sandstone and mud and preserved in a mummified state as a film of organic matter,” Brock explains. “There’s actually not only the impression, but underneath the impression is a film of organic matter one micrometre in thickness.
“He said he wants to come to my lab and extract molecules from it and to figure out whether they are animals or not by looking at the fossilised fat molecules. I thought this cannot work. It’s impossible. I couldn’t believe that he has organically-preserved Ediacarans, because that doesn’t exist. But, of course, it worked,” Brock laughs.
The key is in the fat molecules, or sterols. Animals make cholesterol, plants make sitosterols and fungi make fungal sterols. If you find fossilised cholesterol, then it is a sure sign that what you have is an animal. This is exactly what Bobrovskiy and Brock found. An abundance of fossilised cholesterol shows that Dickinsonia is an early animal.
Their discovery, published in 2018, made waves and is in the Guinness Book of World Records as the oldest confirmed animal in the fossil record.
Read more: Multi-celled animals may have evolved thanks to “wildly fluctuating” oxygen levels a billion years ago
But the palaeontologists were not done yet.
“Then we thought maybe we can tease more information out of these fossils,” Brock says. “Another fossil, called Kimberella, was already known to be the most complex of all Ediacarans and the one contender that could be a modern animal. Kimberella looks like a sea slug. It might have been a mollusc, but it might have been something completely different.”
Kimberella is known to have been able to move itself – a remarkable feat at this stage of animal evolution – and had a kind of snout that scientists presume it used to scrape the microbial mat on the Ediacaran sea floor. Scrape marks in the algae have been found near Kimberella fossils.
Why would it be scraping the mat? Brock suggests that it was probably feeding. “Based on the fossilised scrape marks in front of it, we think it had a mouth.”
“Unless it died of starvation, the gut was probably pretty full,” says Brock. “But this Ediacaran was covered by sediment, so we should be able to see what it has eaten. Because everything is just compressed into a micrometre-thin film, you can’t see anything. What we needed to do was take the entire organic matter from Kimberella and analyse all the molecules in it.”
The scientists developed a technique to tell apart the molecules from the surrounding microbial mat, from Kimberella itself, and from the animal’s gut. They were able to do this by looking at the arrangement of carbon atoms in the fossil molecules.
“Different sterols all have a different of carbon atoms,” Brock explains. “They’re easy for us to distinguish. When we die and decay, these molecules decay as well to become molecule fossils. Their three-dimensional structure changes. They buckle up in different shapes.
“From research that people do on sewage plants, we know in which way molecules in different environments buckle up,” Brock adds. “We found that molecules that decay under oxygen in the mat buckle up in a certain way, molecules that are produced in a decaying animal carcass produce a different type of 3D structure.
”We could see the cholesterol of Kimberella buckled up in the typical carcass way, and we could see algal sterols and bacterial molecules buckled up in the typical gut way. They were all mixed together, but because of their different 3D structure, we could say this is from a gut, this is from Kimberella, and this is the background signal from the non-digested microbial mat.”
Not only did they discover the first meal, but Brock says the findings shed light on the feeding habits of early animals.
“Algae are a pretty efficient food source for animals,” Brock adds. “So, it may be quite significant that what they were eating was algae.”
Brock also explains that Kimberella appears to have had a digestive system that was capable of selecting the sterols it needed to absorb into its tissue, while discarding the unusable molecules. “We can see this because the cholesterol is lacking this typical gut signal. So, it’s taken out before the bacteria could eat it. That means that Kimberella already has this pretty sophisticated way of feeding.”
On the other hand, when a similar analysis was done on 13 Dickinsonia fossils from the same region, there was no evidence of a gut.
“This means it was eating in a different way,” Brock explains. “The most plausible explanation is, because we have this fossilised ‘footprints’ of Dickinsonia lying on the floor, it was sitting there and digesting the mat underneath and taking up the food through the skin on its belly.”
Do you care about the oceans? Are you interested in scientific developments that affect them? Then our new email newsletter Ultramarine, launching soon, is for you. Click here to become an inaugural subscriber.