One of the scientists I met at the annual meeting of the American Association for the Advancement of Science in Chicago last month was Paul Tafforeau, a physicist at the European Synchrotron Radiation Facility in Grenoble, France. He was speaking about various ways in which he's using the synchrotron's powerful X-rays to get more out of fossils than has ever been possible before, from identifying new species of insects preserved in amber, to checking the microscopic structure of early hominid teeth.
So I was interested to see a paper with his name on it out this week, reporting the first fossil brain ever discovered (the brain's soft tissue generally degrades shortly after death). The brain in question belongs to a 300-million-year-old fish called Sibyrhynchus denisoni, and I've written a story on it for New Scientist, which you can read here.
Tafforeau X-rayed four iniopterygian fish fossils from the Carboniferous period for Alan Pradel and colleagues from the National Natural History Museum in Paris, who were hoping to work out the size and shape of the fish's brains from the structure of their skulls. The fossils were found twenty years ago in Lawrence, Kansas.
Tafforeau's imaging allows a 3D computer reconstruction to be made of each fossil, and when Pradel checked through the virtual skulls he saw something "like a ghost" inside one of the brain cases. So Tafforeau scanned it again, using a new technique called holotomography. This takes a conventional X-ray image but then combines it with a technique called phase contrast imaging, which analyses interference patterns created when X-rays are slowed down by areas of varying density within the object being studied.
This time the mystery structure showed up clearly (see video above). I called Pradel and his supervisor Philippe Janvier in Paris last week to ask them about their find, and Pradel told me that at first he was convinced it was just an artefact, because for the brain to survive would be so "surprising and exceptional". But then he recognised various brain areas, including the cerebellum, spinal cord and optic lobes and realised he had come across something very special. The clincher was the fact that even various nerves that protrude from the brain, including the optic nerves, were visible in exactly the right locations. "It was really staggering," says Janvier.
The most important thing about this find, though, isn't this particular brain but that now researchers know it's possible for the structure of ancient brains to be preserved - and in incredible detail. It isn't clear why this brain didn't degrade as has happened in every other fossil found, but it's probably something to do with a film of bacteria that coated the brain after death. Palaeontologists studying fossils from similar sites (black shale, from what was once a coastal sea bed) will now be licking their lips in anticipation for similar finds - the ultimate prize would be a brain from a creature with no living relatives, such as the huge armoured fishes of the Devonian period (400 million years ago), or Tiktaalik, the fish that first crawled onto land. I was quite shocked to find from Janvier that a Walmart now stands on the site in Kansas where the fossils from this study were found, so there's no chance of looking for more fossils there. But there are other similar locations, for example in Oklahoma.