The fossil of an extinct marine spider, discovered in China 520 million years after it lived in the ocean, has helped scientists solve an ancestral puzzle on where the anthropod fits on the evolutionary map.
Using comparisons of central nervous systems, scientists were able to prove that megacheirans, the name given to the extinct group, are related to chelicerates, which include spiders and scorpions, according to a study in the journal Nature today. The findings also show that the 3-centimeter-long (1.2-inch-long) spider’s ancestors branched off from the family tree of other arthropods, which include insects, crabs and millipedes, more than half a billion years ago.
“For the first time we can analyze how the segments of these fossil arthropods line up with each other the same way as we do with living species,” said Greg Edgecombe, a researcher of invertebrates and plants at London’s Natural History Museum and a co-author of the study.
An analysis of the fossilized creature’s nervous system showed similarities to today’s horseshoe crabs and scorpions, suggesting it once dwelled among ancestors of crustaceans, Nicholas Strausfeld, a professor in the University of Arizona’s department of neuroscience and senior author of the study, said in a statement. It had an elongated body with a dozen pairs of appendages that helped it to swim, as well as a scissor-like appendage on its head that was probably used to sense its environment or to grasp, researchers said.
The team analyzed the fossil by applying different imaging techniques, taking advantage of iron deposits that had accumulated in the nervous system during fossilization. The remains are of the earliest known complete nervous system, according to the release that accompanied the report.