Solve the mystery of our animal ancestors

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The contents of the last meal eaten over 550 million years ago have unearthed new clues about the physiology of our earliest animal ancestors like Dickinsonia and Kimberella.

According to scientists at the Australian National University (ANU), the contents of the last meal eaten by the first animals known to inhabit Earth, such as Dickinsonia and Kimberella, can tell us a lot about our animal ancestors.

Dating back 575 million years, Ediacara biota are the oldest large organisms in the world and researchers have found they eat bacteria and algae from the ocean floor.

The findings, published in Current biologyreveal more about these extraordinary creatures, including how they could consume and digest food.

Kimberella had a mouth and guts like modern animals

Scientists have analyzed ancient fossils containing preserved phytosterol molecules – natural chemicals found in plants – left over from the animals’ last meal.

By examining the molecular remains of what the animals ate, the researchers confirmed that the slug-like organism known as Kimberella had a mouth and gut and digested food the same way animals do. modern. They think it was probably one of the most advanced Ediacaran creatures.

The ANU team discovered that another animal, which reached 1.4 meters in length and had a rib-like design imprinted on its body, was less complex and had no eyes, mouth or intestine. Instead, the unusual creature, Dickinsonia, absorbed food through its body as it crossed the ocean floor.

Animal ancestors before the “Cambrian explosion”

“Our findings suggest that the animals of the Ediacara biota, which lived on Earth before the ‘Cambrian explosion’ of modern animal life, were a mixture of crackpot diehards, such as Dickinsonia, and more advanced animals, such as Kimberella that already had similar physiological properties to humans and other animals today,” said lead author Dr. Ilya Bobrovskiy of GFZ-Potsdam in Germany.

Kimberella and Dickinsonia have structure and symmetry unlike anything in existence today. They belonged to the Ediacara family of biota that lived on Earth about 20 million years ago before the Cambrian Explosion – a major event that forever changed the course of evolution of all life on Earth.

Ediacara biota are the oldest fossils large enough to be seen with the naked eye

“The Ediacara biota are truly the oldest fossils large enough to be seen with the naked eye, and they are the origin of us and all animals in existence today. These creatures are our visible roots. deeper,” said Dr. Bobrovskiy, who completed the work as part of his PhD at ANU.

Study co-author Professor Jochen Brocks, of the ANU School of Earth Science Research, said algae are rich in energy and nutrients and may have played a key role in the growth of Kimberella.

Why was the Ediacara biota so large?

“Energy-dense food may explain why Ediacara biota organisms were so large. Almost all of the fossils that preceded Ediacara biota were single-celled and microscopic in size,” Prof Brocks commented.

Using advanced chemical analysis techniques, ANU scientists were able to extract and analyze the sterol molecules contained in the fossil tissues. Cholesterol is the hallmark of animals, and this is how in 2018 the ANU team was able to confirm that the Ediacara biota are among our earliest known ancestors.

The molecules contained telltale signatures that helped researchers decipher what the animals ate before they died. Prof Brocks said the hardest part was telling the fat molecule signatures of the creatures themselves, the remnants of algae and bacteria in their guts, and the decaying algae molecules from the bottom of the ocean. ocean that were all buried together in the fossils.

“Scientists already knew that Kimberella left feeding marks by scraping the algae covering the seabed, which suggested that the animal had a gut. But it was only after analyzing molecules from the gut of Kimberella that we were able to work out exactly what she ate and how she digested food,” Prof Brocks said.

It was a Eureka moment for us

“Kimberella knew exactly which sterols were good for her and had an advanced gut to filter out everything else.

“It was a Eureka moment for us; using a chemical preserved in fossils, we can now make the gut contents of animals visible even if the gut has long since decayed. We then used this same technique on stranger fossils like Dickinsonia to figure out how it fed and found that Dickinsonia had no gut.

Dr Bobrovskiy recovered the Kimberella and Dickinsonia fossils from steep cliffs near the White Sea in Russia in 2018. This is a remote part of the world, home to bears and mosquitoes.

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