Paleontologists at Cambridge University have announced the discovery of the first known fossilized dinosaur brain tissue — ever. It’s a small fossil, and a huge deal.

The rock, just a few inches long, was picked up in 2004 by fossil hunter Jamie Hiscocks on a beach in the south of England after a storm. Since then, paleontologists have been working on making a solid case that it is what they think it is: exquisitely preserved tissue from the outer layer of the brain of an iguanodon, or similar dinosaur that lived 133 million years ago.

Fossils that wash up on shore have already lost a lot of important information about their origin, often changing shape, and making it difficult to figure out what it originally was. But the evidence — at least for this piece of detritus — is all pointing in one direction.

The rock fits neatly into the brain cavity of an iguanodon, based on known fossils, and it likely came from the Tunbridge Wells Sand Formation, which is 133- million-years-old, and coincides with when iguanodons would have been hanging out in the area.

 Based proportionally on a skeletal drawing by Gregory Paul (2008). • This was for a long time classified Iguanodon atherfieldensis.
The brain might have belonged to an animal that looked something like this.

The soft tissues on the outer layer of the fossil are exquisitely preserved — you can even see the blood vessels running through it. The patterns match what we see today in the closest living relatives of the dinosaurs: crocodiles and birds.

Soft tissue fossils from the dinosaur era are rare finds and require very special circumstances for preservation. Although fossilized stomachs, skin, feathers, and even blood vessels have been found, many scientists would have said we’d never find a brain — until we did.

Cambridge paleontologist David Norman, who announced the discovery at the Society of Vertebrate Paleontology’s annual meeting in Utah this week, theorizes that the animal died and sank to the bottom of a shallow, stagnant pond. It flipped over on its head, which became buried in the muck. The conditions in the pond would have had to be inhospitable to bacteria in order for the tissue to stay intact long enough to become mineralized.

Environmental scanning electron microscopy images of tubular structures on the exterior of the Bexhill iguanodontian cranial endocast and within the outer laminar layer, interpreted here as meningeal blood vessels.
Scanning electron microscopy images show what appear to be meningeal blood vessels on the surface of the fossilized brain.

In Norman’s telling, the main mass of the brain ultimately eroded, and was replaced with sediment. The fossil, as it exists today, is mostly made up of debris, preserved in the shape of the brain casing, and enveloped by a very thin layer of fossilized brain material.

This last point was one Norman debated for years with Oxford paleobiologist Martin Brasier, who was involved with the find at an earlier point, and theorized that perhaps the brain had been fossilized in its entirety. Brasier died suddenly in a car crash in 2014, although he left behind notes later found by a former student that indicated he had come around entirely to Norman’s point of view.

The discovery of the fossil will be published in a special edition of Earth System Evolution and Early Life, honoring Brasier’s life and contributions to science.

This brain will certainly be the focus of intense research and debate among paleontologists for years, and decades, to come. Assuming the findings hold up to the scrutiny, this fossil will open up new possibilities into the study of the physical structure of dinosaur brains, and what they might have been thinking.

Photos via I,Steveoc 86/Wikimedia, David Norman, Jamie Hiscocks