Almost all fossils represent the hard parts of long-gone animals: teeth, shells, bones and others. But palaeontologists do occasionally find fossilised soft tissue, too. This remarkable fossil was the first to be described where the brain and parts of the nervous system are visible – astonishingly – after more than 500 million years! Fuxianhuia protensa, an ancient shrimp-like arthropod, and it is clear even from these traces that it had a developed, complex brain similar to those we see in crustaceans and insects today. The brain, seen in black in the top image and in red at the bottom, was spotted in so-called Lagerstätten fossils found in China. Discoveries like these can help evolutionary biologists better understand animal diversity by comparing fossil characteristics to living species: the brain anatomy of F. protensa indicates that the ancestors of brachiopods, another group related to the arthropods, may have had such complex nervous systems but then lost them during the evolution of the group. Until now, it was very challenging to determine how brachiopod brains had evolved due to the lack of fossils, which give us a much better indication of ancestral conditions.

Image courtesy of Xiaoya Ma, Nicholas Strausfeld and Current Biology. You can read more about this work here.

Arthropod: A member of the phylum Arthropoda, which contains insects and crustaceans.

Brachiopods: Members of the phylum Brachiopoda, soft-bodied marine animals with a two-part shell.

Lagerstätten: Fossils from sedimentary deposits which shows exceptional preservation – either as an extraordinary collection of specimens, or (more famously) of soft tissues such as muscles, imprints or nerves.