Science: Brain fossil found in ancient fish skull from Kansas

Researchers imaging the fossil of a 300-million-year-old fish from Kansas have unexpectedly found a fossilized brain in the animal's skull " the oldest known brain found to date.

The find was a double surprise, said co-author John G. Maisey, a paleontologist at the American Museum of Natural History in New York.

First, most specimens of the early fish, known as an iniopterygian and distantly related to modern sharks and ratfishes, are squashed flat and reveal no details of skull anatomy. And, second, brain tissue, unlike that of other organs, is rarely preserved, in large part because it is mostly water.

In this case, researchers have only the fish's head. Because of the preservation, Maisey speculated that the head was bitten off by a predator, which died shortly thereafter. The high concentration of phosphates " which are crucial in making fossils " in the predator's intestines probably caused the skull to be fossilized quickly before it could be crushed, and also preserved the brain, Maisey said.

Paleontologist Alan Pradel of the Museum National d'Histoire Naturelle in Paris, performed an initial examination on four iniopterygian skulls from Kansas and Oklahoma and found that one had an unusual "blob" inside it. He sent it to Paul Tafforeau of the European Synchrotron Radiation Facility in Grenoble, France, who used intense X-irradiation to make a three-dimensional image of the tiny brain.

The fish itself would have been small enough to fit in the palm of a human hand. It is marked by a proportionately massive skull with two large eyes, sharklike teeth in rows, tails with clubs and pectoral fins that were nearly on its back.

The brain itself is pea-sized and much smaller than the brain case, a feature that is preserved in modern descendants. Imaging with the synchrotron, which was reported Tuesday in the Proceedings of the National Academy of Sciences, clearly showed the cerebellum, spinal cord and optic lobes, among other parts. The only part that appears missing is the forebrain, which was perhaps too thin to become mineralized.

The brain has a large lobe for vision and an optic nerve that stretches to the proper place on the brain case, compatible with the large eyes, which were probably used for hunting.

The auditory section of the brain is small, which is compatible with the observation that the ear canal has only horizontal loops for balance, not the three big loops present in modern species. That means the fish's brain could detect side-to-side movements, but not up-and-down ones.