Thursday, January 27

The first animal to inhabit the Earth, sponges from 890 million years ago? | Science



Some marine sponges related to those used in the shower could be the first animals that inhabited the Earth. In an investigation published in the prestigious magazine Nature The remains found in mountains in northwestern Canada date back to about 890 million years. This involves anticipating the appearance of the metazoans (kingdom Animalia) at 350 million. The finding is questioned by some, but supported by others.

Laurentian University researcher (Canada) Elizabeth Turner has spent almost 30 years studying layers and layers of the Mackenzie Mountains, in the American Northwest. Now they are almost 3,000 meters high, but for millions of years they were under the sea. His greatest interest has placed him in the area called Little Dal. With a thickness of 500 meters and a dozen kilometers in diameter, what today looks like stone, were actually reefs formed by calcimicrobials, fossilized calcareous microorganisms. So all life on Earth was microbes like these and microscopic algae.

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Now, on the margins of these reefs, Turner has found another fossilized material with a structure that did not fit with bacteria but with another new form of life. “They are not like the usual fossils you might see in a museum, like shells and exoskeletons; They are not hard mineralized parts created by animals during their lifetime. On the contrary, what is conserved are small masses that contain a microscopic network of small tubules that are joined together. [anastomosis]. It is the complexity of the three-dimensional mesh that is so unusual and complex for rocks of that age, ”he says. “The branching and gathering pattern of this network is quite distinctive: it is different from the types of branching known from other types of organisms that might have been present, such as bacteria, algae and even fungi. But it is almost identical to the meshes that have been described from more recent sponge fossils and to the spongy skeletons of today’s demosponges, ”he adds.

“The branching and gathering pattern of this network is different than the types of branching known from other organisms that might have been present, such as bacteria, algae, and even fungi. But it is almost identical to the meshes that have been described of more recent sponge fossils “

Elizabeth Turner, author of the study published in ‘Nature’

There is a high scientific consensus on the marine sponges (poriferous) as the first animals that inhabited the Earth. As there is when considering them the ancestors of all forms of life that today make up the Animalia kingdom, from fish to birds, through mammals, mollusks or reptiles. But they don’t appear in the fossil record until about 540 million years ago. So Turner’s finding would set the clock of animal emergence back by 350 million years, until the Neoproterozoic era.

But the thing is not that easy. Martin Dohrmann, an evolutionary biologist at the University of Munich (Germany) recalls this when he says that “the interpretation of these structures as sponges is certainly controversial and will not be universally accepted by the scientific community.” But if it were to do so, “it would also mean that the ancestor of all modern animals had an anatomy very similar to a keratose demosponge, which in fact would be a truly remarkable finding”, adds Dohrmann, for which this would mean that modern demosponges “could be considered as a species of living fossils ”. However, the German scientist insists that it would be necessary to discover “more and better conserved structures like these in different locations and neoproterozoic strata to determine their true affinities.”

Even more doubts have the biologist at the University of Lausanne (Switzerland) Jonathan B Antcliffe, whose scientific career is focused on the appearance and evolution of sponges. “Your interpretation is wrong. It’s about microbialites [acumulación de material microbiano mineralizada y petrificada]. It has not demonstrated any of the differential characteristics of sponges. And these fossils are featureless tubes. Any form of life can make tubes without distinctive characteristics ”, he opines. “The fossils were found with a lot of microbial fossils, so they probably are too,” he adds. Among those details that Antcliffe is missing are the absence of spicules, such as spikes or twigs that stand out from the structure or traces of the characteristic pores of the sponges.

“The interpretation of these structures as sponges is certainly controversial and will not be universally accepted by the scientific community”

Martin Dohrmann, evolutionary biologist at the University of Munich

In favor of the conclusions of the research published in Nature there is the researcher at the University of Göttingen (Germany) Joachim Reitner. This geobiologist has specialized in studying microbialites, such as the Little Dal reefs. Reitner, who has reviewed the Canadian scientist’s article before its publication, is convinced that “what Liz Turner has found are remains of keratinous sponges.” And he adds: “I would need a whole scientific article to collect all the arguments that make me believe that it is remnants of demo-sponges.”

So the key to the controversy is not in the dating, which is correct, but in knowing if those marks of a few fossilized microns (see image above) are from the first sponges. Turner herself is very cautious and admits to having her own doubts: “Yes, it is possible that there is another explanation, something unknown, that we have not found yet, so I do not want to imply that this is the last word. But I think the really striking similarity of the 890-million-year-old mesh to that of more recent sponge fossils and modern sponges is a compelling analogy. ” And she concludes: “My purpose now that I was finally ready to present this material was to offer a possibly interesting and possibly important new perspective on the question of the initial evolution of animals; now it’s up to the scientific community to discuss ”.

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