It always seemed impossible for animal tissue, like organs and brains, to become fossilized, because of the delicate nature of tissue.  But now, according to a story on smithsonianmag.com, paleontologists researching in China have documented a group of seven fossilized brains from a species that lived more than 500 million years ago.

These aren’t the first fossilized brains discovered.  Back in 2012, some of the same scientists reported finding a fossilized brain from the same species as the new discovery, a shrimp-like animal called Fuxianhuia protensa.  But the paleontology world was skeptical, since only one specimen was found.  Many thought it was something left behind by experiments.

But with the discovery of seven more specimens, the scientific world is taking notice.

The conditions would have to be almost perfect for soft tissue to become fossilized.  The dead animal would have to be encased in something to prevent scavengers from eating the tissue in the first place.  Then, it would take extreme pressure to force the water completely out of the tissue, and the matter would have to be in a low oxygen environment to prevent microbes from decomposing the tissue.

Many well-preserved fossils from the area in which these new discoveries were made, the Chengjiang Shales in southwest China, have been buried in underwater mudslides, sealing them off from the outside.  That area has been known for years as a depository of many types of fossil remains.

The scientists believe the density of the specimen’s brains was a factor in the preservation as well, saying the arthropods brains were probably similar to today’s crustaceans.

The researchers view the fossilized brains under an electron microscope and found the brains had indeed been flattened over the years into a thin film of carbon, in which the scientists could still see the neural pathways, even after such a long period of time.

In testing their theory, the team ran a series of experiments on sand worms and even cockroach brains to try to mimic the fossilization process, with great success.

The scientists say their new discoveries have led them to some new clues as to how the arthropod brains have evolved over the ages.  The fossils suggest the creatures had an complex brain similar to an insect, instead of a simple clam-like brain as had been previously thought.

The findings of the research was published in Current Biology.