Scientists rule out that the microscopic creature without anus found in China is a human ancestor

• Science They obtain the first images of dolphins feeding in trawl nets

An international team of researchers has discovered that a

discovered in China that humans were thought to be descended from is part of a

.

Saccorhytus

like a wrinkled, spiny sac, with a large mouth surrounded by spines and holes that

, an early feature of the deuterostome group, from which our own deep ancestors arose.

However, extensive analysis of

fossils from China has shown that the holes around the mouth are bases of spines that were dislodged during

, finally revealing the evolutionary affinity of the Saccorhytus microfossil. '.

"Some of the fossils are so perfectly preserved that they

," says Yunhuan Liu, professor of paleobiology at Chang'an University (China).

"

was a curious beast, with a mouth but no anus, and rings of complex spines around the mouth," he adds.

a tiny fossil

The findings introduce important modifications in the

and in the understanding of how life developed.

The true story of

's ancestry lies in the internal and external microscopic features of this tiny fossil.

By taking hundreds of

at slightly different angles, with the help of powerful computers, a detailed 3D digital model of the fossil was reconstructed.

Researcher Emily Carlisle, from the School of Earth Sciences at the University of Bristol (UK), explains that "fossils can be

and Saccorhytus is no exception. We had to use a synchrotron, a type of

, as a basis for our analysis of the fossils."

Digital models showed that the

by another layer of the body extending through, creating spines around the mouth.

"We believe that these would have helped

to capture and process their prey", suggests Huaqiao Zhang, from the Nanjing Institute of Geology and Paleontology (China).

Researchers believe

is actually an

: a group containing arthropods and nematodes.

"We considered many alternative groups that Saccorhytus could be related to, such as corals, anemones and jellyfish, which

," explains Professor Philip Donoghue, from the School of Earth Sciences at the University of Bristol, which co-led the study.

's lack of an anus

is an intriguing feature of this microscopic and ancient organism.

Although the obvious question is the alternative route of digestive waste, this feature is important for a reason fundamental to

.

How the anus arose contributes to the understanding of how animal

evolved .

Moving 'Saccorhytus' from the deuterosome to the ecdysozoon means removing the anus that disappears from the history of the deuterosome and adding it to that of the ecdysozoon.

"This is a really unexpected result because

, which extends from the mouth to the anus. Saccorhytus's membership in the group indicates that it has gone back in evolutionary terms,

they would have inherited ."

their ancestors," says Shuhai Xiao of Virginia Tech in the United States, who co-led the study.

"We don't yet know the precise position of

within the tree of life, but it may reflect the ancestral condition from which

all members of this highly diverse group

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