Oldest Fossil Brain Found in "Bizarre" Prehistoric Fish

John Roach
for National Geographic News
March 3, 2009

Digital x-ray images of a "bizarre" 300 million-year-old shark relative have revealed the oldest known fossilized brain, researchers announced yesterday.

The unusual discovery raises hopes that scientists will find other ancient brains and use them to study how gray matter has evolved, said John Maisey, a paleontologist at the American Museum of Natural History in New York.

"The brain … is remarkably soft tissue—brain tissue is mostly water," Maisey said. "To preserve anything is quite remarkable."

The fossil was found in an iniopterygian, an extinct ancestor of modern ratfishes (see albino ratfish picture), which are distant relatives of sharks and rays. Maisey said the ancient fish, which swam in an ocean that once covered the midwestern U.S., would have fit in the palm of a human hand.

The scans revealed the fish had a pea-size brain much smaller than the braincase itself. This is similar to modern sharks, rays, and chimaera fish, whose brain growth slows as they age, even as the rest of their bodies expand.

The iniopterygian's brain has a large lobe for vision, and the skull has relatively large eye sockets. This suggests the fish "was using its eyes as a major way to locate prey," Maisey said.

In addition, the hearing-related section of the brain is flattened. This reflects the curious arrangement of the iniopterygian ear, which was optimized for side-to-side movement, but not up and down movement.

"It is really a very puzzling fish as to how it would have moved around and what it could have done," Maisey said. "They are really, really bizarre."

Findings published today in the journal Proceedings of the National Academy of Sciences.




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