An international team of researchers has discovered a 520 million-year-old fossilised nervous system in China, which is so well-preserved that even individual nerves are visible, helping unravel how the nervous system evolved in early animals.
Considered the most complete and best example yet found, the nervous system is of a crustacean-like animal that lived more than 500 million years ago. It is the first time this level of detail has been observed in a fossil from this age, experts say.
The findings, published in the ”Proceedings of the National Academy of Sciences” journal, are helping researchers understand how the nervous system of arthropods — creepy crawlies with jointed legs — evolved, a release from the University of Cambridge said.
The animal, called Chengjiangocaris kunmingensis, lived during the Cambrian “explosion”, a period of rapid evolutionary development about half a billion years ago when most major animal groups first appear in the fossil record.
C kunmingensis belongs to a group of animals called fuxianhuiids, and was an early ancestor of modern arthropods — the diverse group that includes insects, spiders and crustaceans, the researchers from UK, China and Germany said.
“This is a unique glimpse into what the ancestral nervous system looked like,” said study co-author Javier Ortega-Hernández of the University of Cambridge’s Department of Zoology. “It’s the most complete example of a central nervous system from the Cambrian period.”
C kunmingensis looked like a sort of crustacean, with a broad, almost heart-shaped head shield, and a long body with pairs of legs of varying sizes. Through careful preparation of the fossils, which involved chipping away the surrounding rock with a fine needle, the researchers were able to view not only the hard parts of the body, but fossilised soft tissue as well.
Like modern arthropods, C kunmingensis had a nerve cord — which is analogous to a spinal cord in vertebrates — running throughout its body, with each one of the bead-like ganglia controlling a single pair of walking legs.
The release said closer examination of the exceptionally preserved ganglia revealed dozens of spindly fibres, each measuring about five thousandths of a millimetre in length.
“These delicate fibres displayed a highly regular distribution pattern, and so we wanted to figure out if they were made of the same material as the ganglia that form the nerve cord,” said Ortega-Hernández. “Using fluorescence microscopy, we confirmed that the fibres were in fact individual nerves, fossilised as carbon films, offering an unprecedented level of detail. These fossils greatly improve our understanding of how the nervous system evolved.”