Fossilised dinosaur brains have been identified for the first time ever, having first been discovered on a beach in Sussex over 10 years ago. Scientists say the "astonishing" find will help them understand the structure of dinosaur brains, as well as how they evolved to what we see today in birds and crocodiles.

Preserved soft tissues of vertebrates and terrestrial organisms are extremely rare in the fossil record. And brain tissue is some of the least commonly preserved soft tissue – mostly because fossilised brains are very rare and easily broken down.

But researchers at the University of Cambridge have now announced the discovery of a brain specimen dating back 133 million years, which was preserved by being "pickled" in highly acidic water and low oxygen just after it died.

"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 study co-author David 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. The chances of preserving brain tissue are incredibly small, so the discovery of this specimen is astonishing."

The brain was found by fossil hunter Jamie Hiscocks near Bexhill in Sussex in 2004. Subsequently, researchers from the UK and Australia analysed it using advanced scanning techniques. In doing so, they were able to identify tough membranes that surround the brain, along with strands of collagen and blood vessels. Scientists also found tissues from the brain cortex and delicate capillaries.

dinosaur brain
Environmental scanning electron microscopy images of tubular structures on the exterior of the fossil. David Norman

The brain tissues belong to an iguanodontian ornithopod dinosaur, a large herbivorous dinosaur that lived during the early cretaceous period.

Scientists say the structure of the fossilised brain is similar to that of modern-day birds and crocodiles. Unlike modern-day reptiles, where the brain only takes up about half the space of the cranial cavity, the tissue of the fossilised brain was pressed directly against the skull, potentially indicating dinosaurs had larger brains, filling more of the cavity.

However, researchers say this is probably not the case. Instead, they think that as the brain decayed it collapsed and was pressed against the roof of the skull. "As we can't see the lobes of the brain itself, we can't say for sure how big this dinosaur's brain was," said Norman.

"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."