A pebble found in Sussex, England was confirmed to be the first example of a dinosaur's brain tissue.

Jamie Hiscocks, a fossil enthusiast, discovered the fossil in 2005. Researchers explained that the brain came from the Iguanodon species.

Iguanodon is a large herbivore that lived during the Cretaceous period 113 million years ago. It resembles the brain tissue of modern-day crocodiles and birds, Reuters reported.

Researchers explained that the meninges, tough tissues in the brain, capillaries and some parts of the cortical tissue were well-preserved. They said that finding a brain tissue is rare that's the reason why it's hard to study the evolutionary history of dinosaur's brain tissue.

Alex Liu from the University of Cambridge explained that they were astonished by the specimen. He explained that the chances of finding a fossilized soft tissue are very dim.

The researchers explained that the brain tissue is well-preserved was probably exposed to a bog or swamp, highly acidic and low-oxygen water, after it died. This mineralized the brain tissues before the brain completely decayed, Science Daily reported. 

David Norman, another researcher, explained that the dinosaur probably died in a body of water. It's had was partially buried in the bottom.

He added that since the body was buried in the water that's highly acidic and has little oxygen, the soft tissue was preserved. He said that the rest of the body was probably buried in the water. 

For this project, researchers used a Scanning Electron Microscope (SEM) to identify meninges that surround the brain. They also used to determine the collagen strands and blood vessels.

They also found structures from the brain cortex, the outer layer of the neural tissue, that's interwoven with the capillaries. They explained that the brain resembles that of a typical reptile.

It's sausage shape that's surrounded by dense blood vessels and thin-walled sinuses, vascular chambers. They added that brain just takes up half of the cranial cavity of the brain.

Despite these findings, researchers explained that it's hard to conclude the brain size of the dinosaur from this specimen. They said that dinosaurs could have bigger brains than they thought of.