Fossils that are almost 900 million years old could be the oldest traces of animal evolution, a study – 07/28/2021 – shows

Filaments of biological origin, preserved in Canadian rocks and nearly 900 million years old, could be the oldest traces of animal development in the oceans, according to a study in the journal Nature. The network of structures would correspond to the “skeletons” of porifers (popularly called sponges), the most primitive invertebrates we know today.

Before the work, the oldest evidence of animal evolution came from rocks that were just over 600 million years old. Thus, if correct, the new research reinforces the hypothesis of a long evolutionary process “in the shadows” that is difficult to see before the first animals took on more complex and varied forms.

“The areas that have been preserved in the limestone as microscopic worm-shaped networks are identical to materials that other researchers have described in much newer rocks, which includes the bodies of the sponges themselves,” explained the study author, Elizabeth Turner of from Laurentian University in Folha., In Canada. “It is a very typical pattern of sponges that is normally not formed by bacteria, algae or fungi.”

Turner examines rocks from northwestern Canada in what is known as the Stone Knife Formation. 890 million years ago, at the beginning of the phase of Earth’s history known as the Neoproterozoic, the region had large reefs formed by microorganisms in medium and shallow waters – probably photosynthetic bacteria, like today’s plants.

The reefs had a diameter of up to several kilometers and were 500 m thick. According to the reconstruction proposed by the researcher, the sponges, which were only 1 cm long, grew on the edges of bacterial structures, in less-lit places, or in more agitated bodies of water (two factors that layers very not favored the growth of microbes).

Everything indicates that by the beginning of the Neoproterozoic, sponges were formed from only organic material, with no limestone or silica “skeletons” as is the case with some of their modern relatives. Instead, its structure was made up of a resistant protein called spongin.

When the sponges died and began to petrify, the sponge networks were preserved in the form of tiny tubes filled with crystals of the mineral calcite.

If Turner’s interpretation of the material is correct, how can we explain the long period of animal life “in the shadows” before other invertebrates and vertebrate ancestors appeared 600 million to 500 million years ago?

“It is possible that sponges appeared 890 million years ago, perhaps because they are more tolerant of low oxygen concentrations than more complex animals, while other groups of animals only emerged after the great event of the oxygen supply to the atmosphere and the oceans in the later Neoproterozoic. The possible sponges I have described may have stayed calm in this “nirvana” of the reefs without suffering from evolutionary pressures, ”she muses.

Turner goes on to explain that attempts to “connect the dots” between the two phases of animal evolution are inherently complicated because, among other things, one has to find rocks of the right age that are relatively rare and spend a lot of time analyzing the Tracks under the microscope until fossils are found that will help answer these questions.

“Unfortunately, you need a tolerance for ‘slow science’, which is very rare these days,” she complains.

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