A mysterious, microscopic creature resembling an angry minion has long been believed to be the first human ancestor. However, a study published this Wednesday (17) in the journal Nature found that the microorganism, which had no anus, is part of a phylogenetic tree different from ours, much to the relief of scientists who finally discovered the true evolutionary link of have discovered this species. .
Saccorhytus was a microscopic creature with a spiky mouth like its body and no anus. Image: Philip Donoghue et al.
The tiny creature called Saccorhytus was equipped with a large mouth surrounded by spines and holes that have been interpreted as pores for gills an early feature of the Deuterostomes group from which our deep ancestors emerged.
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However, a comprehensive analysis of 500millionyearold fossils from China has shown that the holes around the mouth are the bases of spines that broke off during the fossil’s preservation, providing revealing new information about the strange creature.
“Some of the fossils are so perfectly preserved that they almost look alive,” says Yunhuan Liu, a professor of paleobiology at Chang’an University in China, in a statement. “Saccorhytus was a strange animal, with a mouth but no anus, and complex rings of spikes around its oral cavity.”
3D digital model of Saccorhytus from different perspectives, created by scientists who discovered its true identity. Image: Philip Donoghue et al.
“Fossils can be quite difficult to interpret, and Saccorhytus is no exception. We had to use a synchrotron, a kind of particle accelerator, as the basis for our analysis of the fossils,” explained researcher Emily Carlisle of the School of Earth Sciences at the University of Bristol, England.
According to her, the synchrotron delivers very intense Xrays that can be used to take detailed pictures of fossils. “We took hundreds of Xray images from slightly different angles and used a supercomputer to create a 3D digital model of the fossils, showing the tiny features of their internal and external structures.”
Digital models showed that the pores around the mouth have been closed by another layer of the body, which expands and forms the spikes that surround them. “We think this would have helped Saccorhytus catch and eat its prey,” said Huaqiao Zhang of the Nanjing Institute of Geology and Paleontology, coauthor of the study.
The researchers believe that Saccorhytus is an Ecdysozoa, a clade that includes arthropods and nematodes. “We consider many alternative groups to which Saccorhytus might be related, including corals, anemones and jellyfish, which also have a mouth but no anus,” said Professor Philip Donoghue of the University of Bristol School of Earth Sciences, who studied the study coled.
“To solve the problem, our computer analysis compared the anatomy of Saccorhytus to all other living animal groups and concluded a relationship to arthropods and their relatives, the group that includes insects, crabs and roundworms,” Donoghue explained.
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The reclassification of the creature without an anus could change what is known about the development of the new group
The absence of an anus in Saccorhytus is an intriguing feature of this ancient microorganism. How the organ arose—and later disappeared—contributes to our understanding of how animal bodies evolved.
And the shift of Saccorhytus from the Deuterostomes group to the Ecdysozoa group changes the direction of research. It is no longer a matter of understanding how the anus would have arisen with the evolution of the species, but how it disappeared.
“This is a really unexpected result because the arthropod group has a gut that extends from the mouth to the anus. Saccorhytus’s membership in the group suggests that it evolved backwards and dispensed with the anus that its ancestors would have inherited,” said Shuhai Xiao of Virginia Tech, who also contributed to the study. “We do not yet know the exact position of Saccorhytus in the tree of life, but this may reflect the ancestral state from which all members of this diverse group evolved.”
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