Brain too can get fossilised

Scientists have long maintained that brains do not fossilise -- but new research has provided the strongest evidence yet that it is possible. In fact, the brains of a set of 520-million-year-old arthropods did just that.

The species, Fuxianhuia protensa, is an extinct arthropod that roamed the seafloor about 520 million years ago. It would have looked something like a very simple shrimp.

"Each of the fossils found at Chengjiang Shales -- fossil-rich sites in southwest China -- revealed F protensa's ancient brain looked a lot like a modern crustacean's," said Nicholas Strausfeld, a Regents' professor in the department of neuroscience at the University of Arizona.

He and his team found that the brains were preserved as flattened carbon films.

This led the research team to a convincing explanation as to how and why neural tissue fossilises.

The only way for an object to be fossilised is for it to be rapidly buried.

Hungry scavengers cannot eat a carcass if the brain is buried faster and as long as the water lacks in oxygen so a buried creature's tissues escapes being consumed by bacteria as well.

Strausfeld and his collaborators suspect F. protensa was buried by rapid, underwater mudslides -- a scenario they experimentally recreated by burying sandworms and cockroaches in mud.

According to Strausfeld, the brain withstood the pressure from being rapidly buried under thick mud because the nervous system must have been remarkably dense.

In fact, tissues of nervous systems, including brains, are densest in living arthropods.

In the paper, Strausfeld and Xiaoya Ma from China's Yunnan University and Gregory Edgecombe from the Natural History Museum in London analysed seven newly discovered fossils of the same species to find, in each, traces of what was undoubtedly a brain.

Strausfeld is now working to elucidate the origin and evolution of brains over half a billion years in the past.

"People, especially scientists, make assumptions. The fun thing about science, actually, is to demolish them," Strausfeld noted in the paper published in the journal Current Biology.