First fossilised brain from a dinosaur

05 November 2016

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The first example of a fossilised dinosaur brain has been discovered in a pebble picked up on a UK beach...

Millions of years ago the region of the south coast of England called Bexhill would have been a seasonal wetland prone to forest fires and home to large herbivorous dinosaurs like iguanodons.

One of them died in this spot and its head sank into the surrounding soft, acidic oxygen-poor mud, which seeped inside the animal's body and replaced the brain with phosphate and carbonate minerals.

Wind forward 133 million years, and fossil hunter Jamie Hiscocks picked up what he thought looked like an interesting stone.

Measuring about 10 by 6 centimetres, the object is a cast from inside the skull of the dead iguanodon.

Although "endocasts" of the insides of dinosaur skulls have been discovered in the past, Oxford University dinosaur specialist Martin Brasier, who examined the specimen, recognised the potential value of the artefact, suspecting accurately that this was more than just the outline of the inside of the skull cavity.

Working with colleagues at the University of Western Australia (UWA), Cambridge University and the Natural History Museum in London, the fossil was examined using an electron microscope and a CT scanner.

What was revealed, preserved inside the cast, are replicas of the outer membranes - or meninges - that once invested the dinosaur's brain.

The blood vessels that ran across the brain surface are visible, and the surface brain tissue itself and the separate brain regions can all be discerned.

Nothing like this has ever been seen before. In life, the animal would have been between 4 and 5 metres long and these species routinely grew to between 6 and 8 metres, meaning this one was about half way to reaching its fully adult size.

But while we have a reasonable insight into the gross anatomy of these creatures, very little is known about their potential behaviours and intellect.

Scientists have based most of their theories on modern-day crocodile brains. Like most reptile brains, these tend to be sausage-shaped and surrounded by a thick "packaging" of meningeal tissues and blood vessels meaning that the brain takes up only about 50% of the space inside the skull.

Intriguingly, this iguanodon specimen does not show the same sort of pattern and the brain seems to extend to abut the skull case, suggesting that these animals may have had significantly larger brains and hence a higher EQ - encephalisation quotient, the dinosaur equivalent of IQ - for their size than we had thought previously.

That said, the researchers point out that it's likely that the dinosaur's head initially came to rest in the mud that preserved it upside down, which could account for the apparent brain enlargement.

The results have been announced in a special publication of the Geological Society of London, in recognition of the work of Martin Brasier, who was sadly killer in a car accident two years ago before the work on the fossil was complete.

"I have always believed I had something special. I noticed there was something odd about the preservation, and soft tissue preservation did go through my mind. Martin realised its potential significance right at the beginning, but it wasn't until years later that its true significance came to be realised," says Hiscocks.

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