In a shale deposit in Kansas, researchers unearthed the intact skull of a prehistoric fish with a surprise inside: the oldest brain ever discovered. The fossilized brain dates from 300 million years ago, and was found in the skull of a fish called an iniopterygian, an relative of sharks and another latter-day species called the ratfish. Iniopterygians were once commonplace in the world’s oceans, living in shallow and muddy marine waters. They measured 50 centimetres (20 inches) at most [AFP].
Researchers were surprised and thrilled by the unexpected discovery. Other soft tissue fossils, such as muscles and kidneys, have been found that date back longer than 350 million years ago, but because the brain is delicate and consists mostly of water, it’s much less likely to be preserved in fossil form, says study co-author John Maisey…. In the fossilization process, the brain itself was replaced with hard minerals, which preserved the shape of the original organ, and the rest of the cavity was filled with sediment, Maisey says. [Scientific American].
Maisey considered himself lucky when he found the intact fish skull, since most fossils are flattened by layers of sediment and rock that accumulate above them. He then sent the skull off for CAT scans as a routine procedure, hoping the scans would reveal details about the brain case which would allow researchers to make inferences about what the brain might have looked like. Instead, the scans revealed a 3-D image of the brain itself.
The remarkably preserved fossil brain shows details such as a large vision lobe and optic nerve stretching to the proper place on the braincase, which fits with the fish’s large eye sockets. But unlike typical ear canals that have three big loops to regulate orientation and balance, the ear canals of the extinct fish only exist on a horizontal plane. That meant the fish could detect only side to side movements, and not up or down [LiveScience]. The findings will be published in the Proceedings of the National Academy of Sciences.
The Loom: The 300-Million-Year-Old Brain: Now in 3-D has more on this finding
80beats: Researchers Find Potential 2,000-Year-Old Brain in Muddy Ditch
Image: A. Pradel