​London, Oct 28 (IANS) Researchers have confirmed an unassuming brown pebble, found more than a decade ago by a fossil hunter in Sussex, as the first example of fossilised brain tissue from a dinosaur.

The tissues resemble those seen in modern crocodiles and birds, said the study reported in a Special Publication of the Geological Society of London.

The fossilised brain, found by fossil hunter Jamie Hiscocks near Bexhill in Sussex in 2004, is most likely from a species similar to Iguanodon - a large herbivorous dinosaur that lived during the Early Cretaceous Period, about 133 million years ago, according to the study.

"The chances of preserving brain tissue are incredibly small, so the discovery of this specimen is astonishing," said study co-author Alex Liu from the University of Cambridge.

According to the researchers, the reason this particular piece of brain tissue has been so well preserved is that the dinosaur's brain was essentially 'pickled' in a highly acidic and low-oxygen body of water -- similar to a bog or swamp -- shortly after its death. 

"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," David Norman from the University of Cambridge, noted.

"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," Norman noted.

Working with colleagues from the University of Western Australia, the researchers used scanning electron microscope (SEM) techniques in order to identify the tough membranes, or meninges, that surrounded the brain itself, as well as strands of collagen and blood vessels.

The structure of the fossilised brain, and in particular that of the meninges, shows similarities with the brains of modern-day descendants of dinosaurs, namely birds and crocodiles, the study said.