Mystery Of 'Mega Claw' Lobster-Spider Solved, Thanks To Image Of Half-Billion-Year-Old Nervous System
A fossil of a 520-million year-old never-before-described ocean creature has solved a long-standing mystery about the ancestors of scorpions and spiders – and has given rise to a new mystery.
The fossil of a 520-million year-old nervous system of a newly discovered ocean creature solves a mystery about the ancestors of modern day spiders and scorpions, paleontologists said Wednesday.
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The Alalcomenaeus fossil, as it is being called, reveals that modern crustaceans' ancestors and modern spiders' ancestors were already present as two distinct evolutionary trajectories 520 million years ago. That means their common ancestor must have existed much deeper in time than thought.
The findings of University of Arizona's Nick Strausfeld and London Natural History Museum's Greg Edgecombe are described in the current issue of the journal, Nature. The paleontologists are hoping to find fossils of animals that have persisted from more ancient times, and they hope to find the ancestral type of both the crustaceans and the spiders. "They had to come from somewhere," Strausfeld said. "Now the search is on."
The nervous system in the fossil, found in China, is not visible to the naked eye. Strausfeld and Edgecombe applied different image processing techniques to demarcate the iron deposits that had accumulated in the nervous system during fossilization.
To render the neural structures visible, the paleontologists used CT-scanning to create 3-D images of the fossil. They used another scanning technique to map the distribution of iron deposits outlining the nervous system.. Then, they overlaid the magenta of the iron deposit scan with the green of the CT scan, discarding any image data not showing up in both scans. After invertng the remaining image, Strausfeld and Edgecombe arrived at a striking negative X-ray like image of the ancient neural system.
"The white structures now showed up as black," Strausfeld said, "and out popped this beautiful nervous system in startling detail."
The startling image has yielded other discoveries as well. After examining the spectacular image, Strausfeld and Edgecombe now believe the large claws of megacheirans eventually evolved into the mouths of spiders.
"The parts of the brain that provide the wiring for where these large appendages arise are very large in this fossil," Strausfeld said. "Based on their location, we can now say that the biting mouthparts in spiders and their relatives evolved from these appendages."
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