Scientists have found one of the oldest and most detailed fossils of the central nervous system yet identified, from a crustacean-like animal that lived more than 500 million years ago.
The fossil, from southern China, has been so well preserved that individual nerves are visible, the first time this level of detail has been observed in a fossil of this age, researchers said.
The findings are helping researchers understand how the nervous system of arthropods – creepy crawlies with jointed legs – evolved.
Finding any fossilised soft tissue is rare, but this particular find, by researchers in the UK, China and Germany, represents the most detailed example of a preserved nervous system yet discovered.
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.
“This is a unique glimpse into what the ancestral nervous system looked like,” said study co-author Dr Javier Ortega-Hernandez, of the University of Cambridge’s Department of Zoology.
“It’s the most complete example of a central nervous system from the Cambrian period,” said Ortega-Hernandez.
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.
The vast majority of fossils we have are mostly bone and other hard body parts such as teeth or exoskeletons.
The central nervous system coordinates all neural and motor functions. In vertebrates, it consists of the brain and spinal cord, but in arthropods it consists of a condensed brain and a chain-like series of interconnected masses of nervous tissue called ganglia that resemble a string of beads.
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.
Closer examination of the exceptionally preserved ganglia showed 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,” Ortega-Hernandez added.
The finding was published in the journal PNAS.