Dinosaur Brain Fossil Revealed for the First Time

A pebble-sized object found in 2004 by a U.K. fossil hunter has just been confirmed as the first known fossilized brain tissue from a dinosaur.

The remarkable discovery, dating to the Cretaceous Period 133 million years ago, offers insight into dinosaur evolution, behavior, intelligence and brain structure.

Scanning electron microscope analysis of the fossil reveals it is a fossilized portion of a brain that belonged to an Iguanodon-like dinosaur. Iguanodon, meaning "Iguana Tooth," was a large, plant-eating dinosaur that lived during the Early Cretaceous. It could grow up to 43 feet long and possibly more, according to some estimates.

David Norman, a University of Cambridge paleontologist, described the fossil's surface as showing "areas of encrusted material that has, under microscopic examination, a curious and highly unusual texture, rather like wrinkled fabric to the naked eye."

Norman said that "wrinkled fabric" is made up of several layers that appear very similar to the meninges - tissue that surround the brain in the brain cavity. The layers of the meninges protect and support the brain's softer tissues.

Animation of the fossilized dinosaur brain tissue (Credit: University of Manchester):

Norman and his team believe that the fossil contains some of the meninges that surrounded the dinosaur's brain, as well as strands of collagen and blood vessels. Structures that could represent tissues from the brain cortex - its outer layer of neural tissue - interwoven with delicate capillaries, also appear to be present.

The brain segment has similarities with the brains of modern-day descendants of dinosaurs, namely birds and crocodiles, strengthening the case that all of these animals are related.

The fossil suggests that the brain was "not a tight fit" in the animal's braincase, Norman said, explaining that, unlike birds, the dinosaur's brain only took up about 50 percent of its braincase's volume.

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At first some of the researchers suspected the dinosaur's brain was quite large, since it looks as though the upper brain membranes were pressed against the braincase wall at the top of the animal's skull.

"But, in fact, the only way this specimen could have been preserved was if the head was upside down and the brain has 'flopped' down onto the braincase roof as it started to decay," Norman said.

Co-author Alex Liu of Cambridge's Department of Earth Sciences added, "The chances of preserving brain tissue are incredibly small, so the discovery of this specimen is astonishing."

The team believes the piece of brain was essentially pickled in a highly acidic and low oxygen body of water shortly after the dinosaur's death. The enormous animal might have keeled over near a bog or swamp. Its cause of death is unknown, but Liu said that "the soft tissues of the brain were likely preserved and cast before the rest of its body was buried in the sediment."

While it's fortunate that where the dinosaur fell allowed part of its brain to be pickled for posterity, Norman points out that the "acidic 'pickling' process would have denatured any of the biological molecules." That means no DNA can now be extracted from the fossil.

Nevertheless, "Any time we get soft tissue preservation in a dinosaur it's cause for celebration since it gives us such a unique window into the biology of these animals," Lawrence Witmer, a professor of anatomy and paleontology at Ohio University who did not work on the research, told Seeker.

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Vertebrate paleontologist Darren Naish of the University of Southampton was not too shocked when he first learned of the fossil's discovery.

Naish said: "The idea that a dinosaur's brain might be preserved as a fossil perhaps seems improbable, but a large number of recent discoveries have shown that soft structures of virtually any kind can be preserved in the fossil record when the conditions are right"

While the Iguanodon-like dinosaur's full brain was probably not as large as first theorized, Naish pointed out that "size isn't everything when it comes to brain organization and function." Honeybees, for example, have very small brains, but are extremely intelligent.

It is, however, possible that this particular dinosaur wasn't the sharpest tool in the shed. Norman said that the dinosaurs on the evolutionary line leading to birds likely had larger brains. They managed to survive the mass extinction event around 65 million years ago.

The find was published in a Special Publication of the Geological Society of London, in tribute to honorary lead author Martin Brasier, a University of Oxford professor who died in a road traffic accident in 2014.

Brasier was one of the first to analyze the fossil, which was found near Bexhill in Sussex by fossil hunter Jamie Hiscocks. Early on, Brasier believed that it was a dinosaur brain, but he thought that the fossil represented a whole brain. Co-author David Norman, a University of Cambridge paleontologist, disagreed and the two "argued long and hard," Norman told Seeker.

"Sadly, he died," Norman said, "but before he did I sent him my detailed interpretation of the specimen. It turned out that he worked through my commentary and after every paragraph he wrote 'agreed.' We resolved our issues. I did not know Martin had done this, but Alex his PhD student found my file on Martin's computer, so this paper is a reflection of our agreement."

Top photo: Fossilized dinosaur brain tissue. Credit: Jamie Hiscocks