An article published in the journal “Proceedings of the National Academy of Sciences” describes a research conducted on five fossils of Chengjiangocaris kunmingensis, a crustacean-like arthropod that lived about 520 million years ago in today’s China. They preserved beautifully, so much that their individual nerves are visible making them the oldest fossils to show such details.
Chengjiangocaris kunmingensis belonged to the Fuxianhuiida order, which includes the ancestors of modern arthropods, from insects to crustaceans. This species lived during the Cambrian explosion period which saw the emergence of today’s phyla. The cases in which part of the soft tissues can be preserved are rare and in the case of arthropods we have especially their exoskeletons. On the few occasions in which parts of the nervous system of such ancient animals fossilized they were parts of their brain.
In 2013, the scientists who have carried out this research identified a fossilized nervous system and detailed exams uncovered interconnected bead-like ganglia. They’re exceptionally preserved with single nerve fibers attached to them. Very accurate exams were necessary because the fibers were only five thousandths of a millimeter long.
Chengjiangocaris kunmingensis possessed a nervous cord like the the spinal cord typical of chordates running through its body. Each ganglion controlled a single pair of its many legs. A fluorescence microscopy exam allowed to establish that the fibers are attached to the ganglia are individual nerves.
Dr. Javier Ortega-Hernández of the University of Cambridge’s Department of Zoology, one of the study authors, stated that this fossil allows us to understand what he an ancestral nervous system looked like. In many modern arthropods it seems to have simplified with the loss of various nerves.
The discovery of exceptionally preserved fossils such as those of Chengjiangocaris kunmingensis allows to better understand the evolution of arthropods’ nervous system. From this point of view, they are by far the best fossils discovered so far and are allowing that kind of research to make a leap forward.
