Fossil-hunter's find identified as preserved dinosaur brain
A "brown pebble" spotted by a fossil hunter in Sussex more than a decade ago has been confirmed as the first known example of petrified dinosaur brain.
The specimen is thought to have come from a large plant eater such as Iguanodon, which lived about 133 million years ago.
Scientists believe the dead dinosaur's head was buried in mud at the bottom of a swamp, allowing its brain to be "pickled" and preserved.
In time the soft tissues became mineralised. But the fossil retained distinctive features such as the meninges - a protective membrane surrounding the brain - blood vessels, collagen and structures thought to represent the outer layer of nerve cells, or cortex.
A detailed study of the "pebble" has revealed similarities with the brains of present-day birds and crocodiles, both close relatives of dinosaurs.
Dr Alex Liu, from Cambridge University's Department of Earth Sciences, who took part in the analysis, said: "The chances of preserving brain tissue are incredibly small, so the discovery of this specimen is astonishing."
The find's importance was first recognised by the late Professor Martin Brasier, from Oxford University, who co-led the research prior to his death in a road accident in 2014.
It is highlighted in a Special Publication of the Geological Society of London published in tribute to the professor, who was one of the world's leading palaeobiologists.
Fossil hunter Jamie Hiscocks, who discovered the specimen on a beach near Bexhill-on-Sea in 2004, and is named as one of the study's authors, said: "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.
"In his initial email to me, Martin asked if I'd ever heard of dinosaur brain cells being preserved in the fossil record. I knew exactly what he was getting at. I was amazed to hear this coming from a world-renowned expert like him."
Dr David Norman, from Cambridge University, who worked with Prof Brasier on the specimen, said the brain tissue had, in effect, been "pickled" in a highly acidic, low oxygen environment - probably a bog, or swamp.
"What we think happened is that this particular dinosaur died in or near a body of water, and its head ended up partially buried in the sediment at the bottom," said Dr Norman.
"Since the water had little oxygen and was very acidic, the soft tissues of the brain were likely preserved and cast before the rest of its body was buried in the sediment."
Typically in reptiles, the brain is surrounded by a dense drainage system consisting of blood vessels and vascular chambers. The brain itself only takes up about half the space within the skull cavity.
But, surprisingly, the tissue in the fossilised dinosaur brain appears to have been pressed directly against the skull. This raises the intriguing possibility that some dinosaurs had larger brains than previously thought.
However the scientists cautioned against jumping to too many conclusions about dinosaur intelligence.
The most likely explanation was that as the brain decayed after death gravity caused it to collapse against the roof of the skull cavity, they pointed out.
Dr Norman said: "As we can't see the lobes of the brain itself, we can't say for sure how big this dinosaur's brain was. Of course, it's entirely possible that dinosaurs had bigger brains than we give them credit for, but we can't tell from this specimen alone.
"What's truly remarkable is that conditions were just right in order to allow preservation of the brain tissue. Hopefully, this is the first of many such discoveries."
Mr Hiscocks was at the centre of controversy in 2006 after the Natural History Museum reportedly turned down his asking price of £750,000 for the fossil.