A small fossil found in 2004 is thought to contain mineralized brain tissue of a dinosaur related to the Iguanodon. This is the first time in history that fossilized soft tissue has been found for a dinosaur fossil. The discovery was made on the beach at Bexhill, Surrey around rocks dating to 133 million years ago, so it could belong to an ancestor of the Iguanodon, a large herbivore that lived about 125 million years ago.
It was previously thought that brain tissue could not be preserved, so this discovery opens up the possibility of more potential finds in the future. However, this tissue was fossilized in a particular way that may be hard to find elsewhere. The brain was more or less ‘pickled’ in a high-acid, low-oxygen aquatic environment, which allowed the soft tissue to be mineralized before decay could occur. Scientists speculate that after the dinosaur died it was buried head first into the lake sediment, which allowed this ‘pickling’ process to being.
The tissue is located on the surface of the 10cm by 5cm fossil and scanning tunneling microscopy showed that there are bundles of collagenous fibers and open tubes resembling capillaries (fine, branching blood vessels). The structure of the tissue is similar to that of modern-day birds and crocodiles, both of which are considered descendants of dinosaurs.
One observation of particular interest is that the structures observed in the fossil are commonly found on the outer tissues of the brain. It was originally thought that dinosaur brains were surrounded by a thick protective membrane, with the actual brain only filling a fraction of the brain cavity, similar to modern-day reptiles. However, analysis of the tissue shows only a thin layer of protective tissue, meaning this dinosaur’s brain may have been bigger than expected. However, one should be cautious when drawing conclusions about intelligence, communication, or behavioral abilities because of brain size. One possibility is that the brain could have been pressed up against the skull cavity during burial, resulting in loss of the thick protective membrane during mineralization.
This discovery of soft brain tissue has sparked the interest of many scientists and is encouraging them to double-check other endocranial casts of dinosaurs – there may be many more discoveries lying in wait in skulls across the globe.