The fossil, most likely from a species closely related to Iguanodon, displays distinct similarities to the brains of modern-day crocodiles and birds. Meninges – the tough tissues surrounding the actual brain – as well as tiny capillaries and portions of adjacent cortical tissues have been preserved as mineralised ‘ghosts’.
Video and 3D scan of the brain here: http://www.abc.net.au/news/2016-10-28/dinosaur-brain-fossil-shows-blood-vessels,/7972180
In regard to the truly rare preservation of the fossilized dinosaur brain, Dr Norman said “Brain tissues are incredibly fragile and it is quite incredible that the animal died in circumstances that uniquely led to their preservation – through a process of ‘pickling’ and then mineral replacement”. Dr Norman continued, “What we think happened is that this particular dinosaur died in or near a body of stagnant water, and its head ended up partially buried in the sediment at the bottom.
Since the water had so little oxygen and was so acidic, the soft tissues of the brain were likely preserved and cast before the rest of its body was buried in the sediment.” Circumstances such as these are astonishingly rare in fossilization, meaning this discovery can provide unique insight into the mind of this 133 million-year-old dinosaur.
1) When this animal died, it likely fell headfirst into water, where its skull turned upside down. That limited the exposure to air. (Brains quickly decompose in the presence of oxygen.)
2) The skull stayed intact, so when a small portion of the brain began to decompose, the chemicals it leeched stayed within the brain case. That decomposition “released nutrients and enzymes, rich in things like iron and phosphate,” Liu explained.
3) Those nutrients and enzymes essentially pickled the other portion of the brain, preserving it. Those nutrient and enzymes also contained the right chemicals to begin the process of mineralization.
4) Perhaps within a few days, Liu explained, the preserved portion — a section just a few millimeters thick that was pressed up against the skull — began to be replaced by phosphate and carbonate minerals. A chemical reaction allowed the minerals to transform the organic material, mimicking their structure.