Fossil with no anus isn’t ‘man’s earliest ancestor’ after all

·2 min read
Saccorhytus coronarius - S Conway Morris / Jian Han / SWNS.com
Saccorhytus coronarius - S Conway Morris / Jian Han / SWNS.com

The earliest ever human ancestor has, for more than five years, been thought to be a tiny prehistoric creature that had no anus and lived more than half a billion years ago.

But new research into the bag-like Saccorhytus coronarius shows that it is not actually the earliest known member of the deuterostome group which also includes humans.

Resembling an angry Minion, the Saccorhytus is a spikey, wrinkly sack, with a large mouth surrounded by spines and holes.

Cambridge scientists in 2017 found the animals in Chinese rocks and the one-millimetre-long organism’s name came from their globular body and large mouth.

“When you look at them under the microscope they look like tiny grains of black rice, frankly,” Prof Conway Morris of Cambridge, who published the first paper, said in 2017.

However, new analysis from an international team of scientists, led by the University of Bristol, has disproved the deuterostome conclusion, saying that the animal does not belong to the same extended family group as vertebrates, but is instead a primitive ecdysozoan.

The team looked at holes around the creature’s mouth, which was previously thought to pore for gills, a telltale sign of a deuterostome.

However, fresh analysis with detailed X-rays found this not to be the case, with the holes actually the bases of spines which have been snapped off during the preservation process.

“We believe these would have helped Saccorhytus capture and process its prey,” says study co-author Huaqiao Zhang from the Nanjing Institute of Geology and Palaeontology.

This finding made it impossible that the purported earliest human ancestor was related to Homo sapiens, with the team looking at what other ancient groups - including the same one as corals and jellyfish, which also have a mouth but no anus -  the creature could belong to.

Writing in the journal Nature the researchers state they believe Saccorhytus’s evolutionary origin is most likely to be the same as the nematode worm; the ecdysozoa.

“We still don’t know the precise position of Saccorhytus within the tree of life but it may reflect the ancestral condition from which all members of this diverse group evolved,” added study co-lead Shuhai Xiao from Virginia Tech.