LONDON (Reuters) - Inside this unassuming piece of rock is the first known example of fossilised brain tissue from a dinosaur.
Using a scanning electron microscope to peer inside, scientists identified the intricate structures of brain tissue.
"This amazing specimen has preserved not only the texture and structure of what are called the meninges, these very tough membranes that surround the actual soft parts of the brain but the mineralisation has also preserved the fine blood vessels running through those textures. And also, the really fine capillaries and a little bit of the cortex of the brain immediately beneath those membranes," said Dr David Norman from the University of Cambridge.
The fossil was found in 2004 on a beach in Sussex, southern England.
It is most likely from a species similar to the Iguanodon, a large herbivorous dinosaur that lived around 133 million years ago.
It's exceptionally rare for soft tissue to be so well preserved that it can be studied.
Researchers believe the dinosaur must have died in a bog or swamp with just the right conditions needed for preservation.
"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, because in these stagnant conditions the acidic nature of the water means that the membranes of the brain itself started to pickle and to harden. And once you've got the hardening of what are otherwise extremely soft tissues, you begin the process of preservation," said Dr Norman.
Palaeontologists say the structure of the brain tissue is similar to that of the modern-day descendants of dinosaurs, such as birds and crocodiles.
The research was published in a Special Publication of the Geological Society of London.