In 2004, amateur fossil collector Jamie Hiscocks was walking along the famous Wealden rocks of southern England searching for amber to bring to Oxford University palaeontologist Martin Brasier. What he found instead was much more spectacular than he could have imagined: a 133-million-year-old piece of dinosaur skull with bits of fossilised brain still inside!

Brasier and fellow palaeontologist David Norman at the University of Cambridge immediately noticed that there was something unique about the fossil. Inside the skull were layers of mineralised material that had a strange ruffled and wrinkled look to them. "It's a little bit like your bed when you wake up in the morning," Norman said while presenting his research at this year's meeting of the Society of Vertebrate Paleontology.

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The find represents the first known example of fossilised brain tissue in a dinosaur. Image: Jamie Hiscocks

Brasier and Norman disagreed for some time over what exactly they were seeing. It took intense technological investigation – involving electron microscopy, CT-scanning and X-Ray spectroscopy – to reveal the intricate details: layers of wrinkly tissue with all sorts of finely preserved structures, including the mineralised remains of tiny blood vessels!

If you could take a peek inside your own skull, you'd find that your brain doesn't sit right up against the surrounding bone. Protective layers called meninges lie in between your skull and the outermost brain tissue, called the cortex. In this fossil, parts of a dinosaur's meninges, and even some bits of the adjacent cortex, appear to have been preserved.

As you can imagine, it's an incredible find. Most animals don't leave behind any fossils at all, and when they do, it's usually limited to bones and teeth. It takes very special circumstances for fossilisation to capture organ tissue, giving us rare and exceptional cases like fossilised fish hearts from Brazil, dinosaur muscles from North Dakota and even fish brains from Kansas.

To leave a brainy legacy, this dinosaur – a plant-eater called an iguanodontian – managed to find itself in just the right spot when it died. "As the animal died, its head must have tipped over into a stagnant pond, and that particular stagnant environment was one that promoted the preservation of the soft tissues," explains Norman. The acidic waters of this Cretaceous swamp "literally pickled" the brain tissues, which were preserved long enough to be replaced by minerals. Voilà! Fossilised brain!

"This isn't a revelation – of course a dinosaur had a brain!" says Norman. "But we're actually seeing some of the textures of the brain themselves, which I never thought we'd ever do."

As Norman introduced this amazing fossil to a packed room in Salt Lake City, Utah, he began by acknowledging the importance of the work of Brasier, who died in a car accident in 2014. Norman said he considered the unveiling of this study "a tribute to Martin, and to many beers, and to disputes we had over how to interpret this specimen".

As with any exceptional discovery, it's important to be critical, and not all palaeontologists are fully convinced of these results. "Confirmation in science is a long process, and this publication is the first step toward that end," Johns Hopkins researcher Amy Balanoff told National Geographic. "I have a feeling that because this is such a sensational find, it will be thoroughly examined by the scientific community."

Palaeontologists have been studying dinosaur brains for decades by looking at the features of their skulls. The discovery of actual preserved brain tissue has many hoping for exciting new revelations. Will this fossil teach us brand new things about dinosaur brain evolution? How about dinosaur intelligence? Only future study will tell, and you can bet this fossil will be placed under the microscope many more times in years to come. 

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