The remains of a tiny brain in the primordial animal's head were discovered by scientists.

The ancient cousin of penis worms and mud dragons, Markuelia Hunanensis, is an example of a fossil from 500 million years ago. Scientists haven't found fossils of the worm-like weirdos in their adult form, but they have found hundreds of pristine embryos that capture different stages of the animal's early development. Each embryo is about half a millimeter in diameter.

Philip Donoghue is a professor of paleobiology at the University of Bristol.


This is the first time that Donoghue and his colleague at the School of Earth and Space Sciences at Peking University have found preserved brain tissue in an embryo. They reported their discovery in the journal.

Reports of brain tissue being found have been controversial because it was thought that nervous tissue couldn't fossilize. Nicholas Strausfeld is a regents professor in the Department of Neuroscience at the University of Arizona in Tucson who was not involved in the study.

It looks like a tissue that is not muscle or gut, so what could it be? Strausfeld spoke to live science. The brain cells are arranged in a ring around the animal's gut.

The embryo was collected from a fossil deposit. The fossil was encased in limestone. The limestone was dissolved with acid and then manually sorted through the microfossils.

Each embryo probably weighs fractions of a gram, but he was dissolving down tons, metric tons, of rock over the years. He said that it was beyond the scope of the 'needle in a haystack' area.


After being liberated from the limestone, the embryos were sent to the Paul Scherrer Institute in Switzerland, which has a particle accelerator measuring about 1,300 feet in diameter. The machine emits radiation when it hurls electrons at the speed of light. The team used high-powered X-rays to take pictures of their embryo.

As the specimen rotates through the beam, it takes 1,501 X-rays. The team can peer inside each embryo without having to open it, thanks to the individual X-rays.

The animal's tough outer shell is what the X-rayed embryos mean. Thin lines of gold crosshatching the inside of each embryo are thought to be evidence ofMicrobes that grew over the animal before it was fossilized.

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The embryo that contained traces of nervous tissue looked vastly different than what the team typically observed. The team believed that the embryo had a ring-shaped brain. The team found remnants of muscle in the tail of the fossil.

Donoghue said that the fabric in the head and tail is very different to what is seen in other samples. It's our job to figure out what on Earth it was because it's a biological structure that was in the original organisms.


Strausfeld told Live Science that the brains of animals like penis worms and mud dragons were likely ring-shaped. The authors noted that it would be surprising if the brain had a different look.

This is the first time that nervous tissue has been found in a Sosten-style fossil. Fossils that are less than 0.08 inch (2mm) long are locked in limestone and are preserved through a process in which the animals' tissue is replaced by calciumphosphate. The process produces a minuscule but highly detailed 3D fossil that only preserves the animal's cuticle.

The paper tells us about the potential for future discoveries. Maybe it is just a matter of going back and looking for it in museum drawers, because nobody had foreseen that you could preserve brains or nervous tissues in calciumphosphate.

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