Scientists unravel the mystery of an anusless creature that may be an ancestor of spiders

Scientists unravel the mystery of an anusless creature that may be an ancestor of spiders

A 500millionyearold spiny, microscopic creature with a mouth but no anus has intrigued scientists.

A group of scientists say they have solved an evolutionary mystery involving a 500millionyearold spiny, microscopic creature that has a mouth but no anus.

When the species was discovered in 2017, it was reported that the tiny fossil of this “sea creature” could be the oldest known ancestor of humans.

The animal, named Saccorhytus coronarius, has been tentatively placed in a group called deuterostomies.

They represent the primitive ancestors of vertebrates including humans.

However, a new study now suggests that Saccorhytus should be placed in a completely different group from other animals.

A team of researchers in China and Britain performed a very detailed radiological analysis of the creature and concluded that it belongs to the group of ecdysozoans which are the ancestors of spiders and insects.

One of the sources of this evolutionary confusion was the animals’ lack of anus.

Researcher Emily Carlisle, who has studied Saccorhytus in depth, told BBC Radio 4’s Inside Science podcast that the subject is still “a little confusing”.

“Most ecdysozoa have an anus, so why not this one?” he asked.

An “interesting answer,” the expert points out, is that an even more ancient ancestor of this entire group had no anus, and that Saccorhytus evolved later.

“Maybe he lost [o ânus] during evolution itself maybe he didn’t need one because he just needed a hole in his body to do everything.

Spines or gills?

The main reason for the “repositioning” of Saccorhytus on the Tree of Life is that when first examined, the holes around its mouth were interpreted as pores for gills (or gills) an early feature of deuterostomes.

When the scientists took a closer look — using powerful Xrays to get a closer look at the millimeterlong creature — they found that these structures were actually the bases of some spines that had broken off.

Scientists studying these fossils try to classify each animal into groups — which work almost like a family tree — to get a picture of where each species came from and how they evolved over time.

“Saccorhytus would have lived in the sea, with its spines near its mouth holding it in the ocean sediments,” explained Carlisle, who works at the University of Bristol in the UK.

“We assume he was ‘sitting’ in an unfamiliar environment, with various animals that would look like some creatures alive today, but others that would be completely alien to us.”

Artistic reconstruction of Saccorhytus coronarius based on original fossil finds.  The real creature was probably no more than a millimeter tall  CAMBRIDGE UNIVERSITY  CAMBRIDGE UNIVERSITY

Artistic reconstruction of Saccorhytus coronarius based on original fossil finds. The real creature was probably no more than a millimeter tall.

PICTURED: UNIVERSITY OF CAMBRIDGE

The rocks containing these fossils are still being studied.

“We can still learn a lot about the environment they lived in,” Carlisle added.

“The more I delve into paleontology, the more I realize just how much is missing. When we think about this creature and the world it inhabited, we are only scratching the surface [do conhecimento].”

The saccorhytus was a pointed, saclike creature with a mouth but no anus

Saccorhytus was a pointed, saclike creature with a mouth but no anus.

PICTURED: P DONOGHU ET AL/UNIVERSITY OF BRISTOL

Listen to the Inside Science podcast on BBC Sounds.