The remains of Chengjiangocaris kunmingensis provide an unprecedented glimpse into the Cambrian nervous system.
Our planet has been teeming with life since the Cambrian explosion over half a billion years ago, but the vast majority of these bygone Earthlings have long since vanished without a trace. Indeed, even when species are entombed in the fossil record, scientists are typically bequeathed only their bare bones, stripped of finer details like internal organs and soft tissues.
But despite this overall miserly attitude, the fossil record sometimes does us all a solid by setting aside an extraordinary gem. The remains of Chengjiangocaris kunmingensis, a crustacean-like animal that lived 520 million years ago in what is now Xiaoshiba, China, fits that bill perfectly.
Not only is the species's hard exoskeleton frozen in time, but its nervous system is outlined with such intricacy that even individual nerves are distinguishable. Behold, the most detailed example of a preserved nervous system ever discovered.
As you can see, the animal's ventral cord, which is the purplish line running down its center, is clearly visible. Moreover, a new study published in the Proceedings of the National Academy of Sciences reveals the tiny fibers that comprise the animal's bundled ganglia are also detectable with precision instruments. For perspective, these fibers are about 5,000 times smaller than a millimeter.
That level of soft tissue preservation is almost unheard of, especially from the distant period, when life on Earth first blossomed into the rich biodiversity we experience today. But the Xiaoshiba fossil deposit, located in China's Yunnan Province, is packed with these Cambrian period gems, and remains relatively underexplored compared to more famous formations like the Chengjiang deposit.
"[U]nder normal circumstances it is extremely difficult to obtain preservation of soft tissues, as these decay rapidly and lose most of the morphological information," study co-author Javier Ortega-Hernández, a research fellow at the University of Cambridge, told me over email.
"However, there are cases in which the environmental conditions are more prone to produce exceptional preservation," he said. "These include when the animals are entombed rapidly by a large amount of fine sediment, and all of this occurs in an oxygen-depleted environment. This process helps to limit the extent of decay on the carcasses and may result in the superb preservation of delicate features such as the ventral nerve cord and other parts of the internal anatomy."
This window into inner workings of a Cambrian creature provides tangible insights about the early evolution of the nervous system. For instance, C. kunmingensis was an ancient ancestor of arthropods, the invertebrate group that includes insects, arachnids, and crustaceans.
Studying the extinct animal's nervous system demonstrated that some of the species's modern relatives, like velvet worms or penis worms, maintain a similar internal structure. Others, like the indestructible tardigrades (or water bears), have done away with the complex rubric of nerve fibers found in their Cambrian forebears, in favor of more minimalistic systems. These insights capture a broader evolutionary picture through the aperture of C. kunmingensis's fossilized nerves.
To that point, research into these specimens has only just begun, and scientists hope to extract more information from the stunning remains of this proto-arthropod.
"C. kunmingensis is known from large populations that are still under study," Ortega-Hernández told me. "Although it is very preliminary to evaluate the results of these investigations, the fact that there are several individuals with good preservation that correspond to different age groups is likely to provide new information on the growth of these early arthropods."
"Of course, there is always the possibility that we will be able to find new specimens that show previously unknown features, so only time can tell what C. kunmingensis and other fossils from the Xiaoshiba have to reveal."