Fossils almost 900 million years old may be the oldest traces of animal evolution, study points out – 07/28/2021 – Science

Filaments of biological origin preserved in Canadian rocks, nearly 900 million years old, may be the oldest traces of animal evolution in Earth’s seas, according to a study in the scientific journal Nature. The network of structures would correspond to the “skeletons” of porifers (popularly known as sponges), the most primitive invertebrates we know today.

Before the work, the oldest evidence of the evolution of animals came from rocks just over 600 million years old. Therefore, if the new research is correct, it strengthens the hypothesis of a long evolutionary process “in the shadows”, difficult to detect, before the first animals acquired more complex and diversified forms.

“The areas preserved in the limestone rock as a microscopic vermiform network are identical to materials described by other researchers in much more recent rocks, which include the bodies of the sponges themselves”, explained the study’s author, Elizabeth Turner, from Laurentian University to Folha. , In Canada. “It is a very typical pattern of sponges, which is not usually formed by bacteria, algae or fungi.”

Turner studies rocks that come from northwestern Canada, in the so-called Stone Knife formation. 890 million years ago, at the beginning of the phase of the Earth’s geological history known as Neoproterozoic, the region had large reefs formed by microorganisms in medium and shallow waters – probably photosynthesizing bacteria, like today’s plants .

The reefs were up to several kilometers in diameter and 500 m thick. According to the reconstruction proposed by the researcher, the sponges, which reached only 1 cm in length, used to grow on the edges of bacterial structures, in less lit places or with more agitated waters (two factors that did not favor the growth of microbe layers very much).

Everything indicates that sponges from the beginning of the Neoproterozoic were formed only by organic matter, without limestone or silica “skeletons”, like those of some of their modern relatives. Instead, its structure was made up of a resistant protein called spongin.

When the sponges died and began to fossilize, the spongin 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 to explain the long period of animal life “in the shadows” before other invertebrates and vertebrate ancestors emerged, between 600 million and 500 million years ago?

“It is possible that sponges, perhaps because they are more tolerant of low oxygen concentrations than more complex animals, appeared 890 million years ago, while other groups of animals only emerged after the great event of oxygenation of the atmosphere and seas in later Neoproterozoic times. The possible sponges I described may have stayed quiet in this ‘Nirvana’ of reefs without suffering evolutionary pressures,” she ponders.

Turner further explains that efforts to try to “connect the dots” between the two phases of animal evolution are inherently complicated because one has to, among other things, find rocks of the right age, which are relatively rare, and spend a lot of time analyzing the traces under the microscope until finding fossils that help answer these questions.

“Unfortunately, there needs to be a tolerance for ‘slow science’ which is very rare these days,” she laments.​

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