Your earliest known ancestor was a weird, sack-like sea creature with no anus

31 Jan 2017

Artist’s reconstruction of Saccorhytus coronarius, based on the original fossil finds. Image: Simon Conway Morris/Jian Han

540m years ago, the human species’ earliest ancestor looked an awful lot different. In fact, it was a tiny, sack-like sea creature.

While some holes still exist within the route that evolution took to reach modern humans, a potential breakthrough has been achieved in trying to detect our earliest ancestor.

In a research paper published in Nature, an international team of academics from the UK, China and Germany undertook biological detective work to trace our origins back to a bizarre-looking creature called Saccorhytus coronarius.

Completely new to science

Lacking any sort of similar characteristics to our own species, the Saccorhytus coronarius was a microscopic sack-like sea creature that existed 540m years ago.

Aside from being the most primitive example of a so-called ‘deuterostome’ that encompasses a number of subgroups, including the vertebrates, the creature is also completely new to science, having been discovered in microfossils from China.

At just 1mm in size, the creature likely called grains of sand on the seabed its home and, to the surprise of the team of scientists, does not seem to have any sort of anus whatsoever.

Other findings made using a powerful electron microscope suggest that the creature’s body was bilaterally symmetrical.

Fossilised sample

The fossilised sample of Saccorhytus coronarius. Image: Simon Conway Morris/Jian Han

In one way, out the same

This characteristic was inherited by many of its descendants, including humans, and was covered with a thin, relatively flexible skin, which suggests it had some sort of musculature to allow it to wriggle around.

When it came to mealtime, the creature would have engulfed whatever food it came across using its large, circular mouth, but its lack of an anus made the scientists question how its digestive system worked.

Additionally, the team identified eight conical openings on its body that may have been the precursor to gills as seen in sea creatures today, but it still didn’t answer the question of waste disposal.

“If that was the case, then any waste material would simply have been taken out back through the mouth, which, from our perspective, sounds rather unappealing,” said Simon Conway Morris from the University of Cambridge.

“To the naked eye, the fossils we studied look like tiny, black grains, but under the microscope, the level of detail is jaw-dropping,” he continued. “All deuterostomes had a common ancestor, and we think that is what we are looking at here.”

Colm Gorey was a senior journalist with Silicon Republic