The spiky creature reminiscent of a mini-monster with a large mouth and no anus does not belong to the earliest ancestors of us humans. Scientists have assumed so far. Now an international team of researchers in the journal “Nature” knows better. Accordingly, due to a misinterpretation of certain body openings, fossils of Saccorhytus coronarius were incorrectly assigned to the animal group of the Neumünder (Deuterostomia), to which we humans also belong.
Elaborate X-rays of hundreds of fossils would have shown that the animal should instead be assigned to the so-called molting animals (Ecdysozoa), which include insects, spiders and tardigrades. A 3D model of Saccorhytus coronarius published by the researchers shows an egg-shaped creature with a centrally located maw that takes up much of the body’s surface area.
Its body is covered with many small and some larger spines. According to the study, the little animal probably lived on the seabed and could probably neither crawl nor crawl. Food intake and defecation took place through the mouth.
The first discovery of Saccorhytus coronarius comes from the Chinese province of Shaanxi. The layer of rock from which the fossil comes is dated at a good 530 million years. The fossil is about a millimeter in diameter. It has holes around its mouth. These were initially interpreted as so-called gill pores, a primeval feature of new mouths. But this interpretation of the openings was wrong, as the researchers led by Zhang Huaqiao from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences now show.
They collected hundreds of other fossils of the same species, some of which were much better preserved than previous finds. The researchers took X-rays of these from different angles and used them to build a 3D model of Saccorhytus coronarius on a computer. The scientists were able to show that the alleged gill pores were in fact the sockets of spines. “We believe these Saccorhytus helped capture and process its prey,” says co-author Huaqiao Zhang.
The fact that Saccorhytus coronarius has no anus is a special feature. The researchers assume that its ancestors had an anus, but that it regressed. How the anus arose in animals – and in some cases disappeared again – is important for understanding the evolution of animals and their bodies.
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