Animals appeared 350 million years earlier than previously thought, fossil find suggests

Microscopic tube-shaped structures suggest the presence of ancient sponges.

Microscopic tube-shaped structures suggest the presence of ancient sponges.
photo: CE turner

Ancient rocks from northwestern Canada have been found containing structures compatible with marine sponges. At 890 million years old, they could be the oldest known Fossils of animals on Earth.

Simple single-celled life forms first appeared on Earth about 3.4 billion years ago, but it took some time for more complex animal life to emerge. The Cambrian explosion of complex life forms occurred around 540 million years ago, which coincided with the earliest undisputed sponge fossils.

in 2018, Discovery Steroids – a well-known biomarker – in rocks dating back 660 million And 635 million years ago, it pushed the emergence of sponges in the Neolithic, at least 100 million years before the Cambrian. Genetic analyzes of modern sponges also point to an early origin of these sea creatures, further reinforcing the idea that sponges were the first animals to appear on Earth.

Paco Cardenas, a biologist at Uppsala University in Sweden, did not participate in the new study but did The sponge expert said This discrepancy between the fossil record, chemical evidence and DNA “has been hotly debated in recent years.” Hence the importance of the recently reported discovery, which has implications for how we understand the origin of all animal life on Earth.

Field site in the Northwest Territories, Canada.

Un filocation in the Northwest Territories, Canada.
photo: Elizabeth Turner, Laurentian University

Elizabeth Turner of Laurentian University in Sudbury, Canada, is the sole author of the new book Nature paper, reporting the discovery of fossil-like structures found in rocks taken from the 890-million-year-old Little Dale Reef in the Stone Knife Formation in the Northwest Territories, Canada.

“If these fossils are confirmed to be sponge fossils, they would certainly be the earliest animal fossils in the fossil record, dating back 350 million years before the Cambrian,” Cardenas said. Explained in an email. This latest discovery “may eventually reconcile these people”. [previous] evidence ”, but it“ also raises new questions, ”he added.

Turner looked at the rocks with a microscope and noticed tube-like structures covered with crystals of the mineral calcite. She argues that these features bear a striking resemblance to the fibrous skeletons of horny sponges, formed from the decay of these ancient creatures. Hot sponges are still around today, and you would probably use one as a bath sponge (so yes, humans can actually be descendants of bath sponges, and as a staunch Spongebob Squarepants fan, I’m actually pretty cool with it.)

Turner was able to rule out other explanations for the microstructures due to the composition of the fossil material.

“It’s made up of tiny tubes that branch out very far from each other and then come together to form a complex three-dimensional network,” she said. in a letter. “Of the branching organisms that might be considered alternative explanations, none have this kind of three-dimensional network – not real algae, not bacteria, or fungi.”

Part of a spongy skeleton of a modern keratosis sponge - literally a bath sponge from Greece.

Part of a spongy skeleton of a modern keratosis sponge – literally a bath sponge from Greece.
photo: CE turner

Meanwhile, horned sponges “have exactly that kind of microscopic network,” Turner added, and this network has also been described in undisputed fossil sponges.

Cardenas to point out that “It should be emphasized that these are not undisputed spongy fossils, as the title of the article suggests.” Indeed, the title of the new article describes them as “possible” sponge fossils, but they “look like the skeletal remains of a spongy protein – called sponges – found today in horny sponges”, but “researchers will await confirmation of other fossils from the same period”, books.

Turner wrote that the oldest animals on the planet were spongy, or at least sponge-like, which is not surprising, “given that sponges are the simplest of all animals today and in the fossil record ”. In addition, “the age of the material that I present is consistent with the predictions of molecular clocks, which indicate the appearance of sponges at this time,” she explains, adding that “the fossil sponge scientists have issued the assumption that we should find this type of material in a meaningful way. Older”. Turner noted that the main findings of this study “are largely exactly what was predicted by several other unrelated lines of work.”

On the other hand, Cardenas said that finding sponge fossils more than 250 million years before the aforementioned steroid sponge compounds appeared was “unexpected.” aCompounds from the same period have been found as the newly reported fossils, but “have not yet been attributed to sponges,” he said, “although their similarity” to sponge compounds “is recognized. ”.

Perhaps most surprisingly, the apparent emergence of ancient sponges 90 million years ago before oxygen in Earth’s atmosphere reached the levels required to sustain animal life – at least we thought. If the new finding can be confirmed, it means that sponges, and therefore complex animal life, appeared before the second two oxygenation events on Earth, i.e. the oxygenation of ancient organisms.

Turner noted: “If I am correct in my interpretation of the substance, the first animals appeared before this event and may have tolerated relatively low oxygen levels.”

The discovery also indicates that the complex life forms were not completely wiped out during the cryogenic ice ages that occurred between 720 Ma. and 635 million years old. It was the so-called Snowball Earth episodes, at a time when the entire surface of our planet, it has been argued, was covered with ice.

If we assume that the new interpretation is correct, it means that sponges existed 890 million years ago, so the question arises: how many fu?did they not exist? As the new research indicates, sponges don’t seem to be bothered by lack of oxygen and intensely strong ice ages, so it’s not unreasonable to suggest an earlier onset.

“The geological record needs more intense questioning, and with a really open mind, to answer these questions,” said Turner.

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