Bizarre ‘Minion-like’ creature with no anus is not earliest known human ancestor after all © Philip Donoghue et al
© Philip Donoghue et al

Bizarre Minion-like creature with no anus is not our earliest known ancestor after all

Published: 17th August, 2022 at 16:00
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The microscopic critters actually belong to a group of animals that includes insects, crabs and roundworms, computer imaging study suggests.

The Saccorhytus, a tiny, spikey sack with a large mouth and no anus is not your great many times over grandparent, an international team of researchers has found.


Previous studies had interpreted the holes that surround Saccorhytus’ mouth as being pores for gills and concluded that it was a deuterostome – a primitive group of animals from which ancient human ancestors emerged.

However, a new analysis of the 500-million-year-old fossils, which consisted of the piecing together of 100s of X-ray images, has discovered that the holes were in fact caused by spines that broke away as the fossils were preserved.

“Fossils can be quite difficult to interpret and Saccorhytus is no exception. We had to use a synchrotron, a type of particle accelerator, as the basis for our analysis of the fossils,” said the study’s co-author Emily Carlisle from the University of Bristol’s School of Earth Sciences.

“The synchrotron provides very intense X-Rays that can be used to take detailed images of the fossils. We took hundreds of X-Ray images at slightly different angles and used a supercomputer to create a 3D digital model of the fossils, which reveals the tiny features of its internal and external structures.”

The researchers then compared the anatomical features of Saccorhytus to creatures on other evolutionary branches of the tree of life and concluded that it was most likely an ecdysoszoan - a group of creepy crawlies that contains arthropods and nematodes.

“We considered lots of alternative groups that Saccorhytus might be related to, including the corals, anemones and jellyfish which also have a mouth but no anus,” said the study’s co-leader Prof Philip Donoghue of the University of Bristol’s School of Earth Sciences.

“To resolve the problem, our computational analysis compared the anatomy of Saccorhytus with all other living groups of animals, concluding a relationship with the arthropods and their kin, the group to which insects, crabs and roundworms belong.”

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.


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