Paleontologists Find Fossilized Dinosaur Brain Tissue

A strange brown pebble found near Bexhill in Sussex, UK, has been identified as the first known example of fossilized brain tissue from a dinosaur.

Brain endocast of an iguanodontian dinosaur found in 133 million year old fluvial sediments of the Wealden at Bexhill, Sussex, UK. Image credit: Jamie Hiscocks.

The fossil, studied by an international team of paleontologists led by Prof. Martin Brasier of the University of Oxford, displays distinct similarities to the brains of modern-day descendants of dinosaurs, namely birds and crocodiles.

“The chances of preserving brain tissue are incredibly small, so the discovery of this specimen is astonishing,” said co-author Dr. Alex Liu, from the Universities of Cambridge and Bristol.

The fossilized brain is most likely from a species similar to Iguanodon, a large plant-eating dinosaur that lived in what is now Europe between 135 and 120 million years ago (Lower Cretaceous period).

“Scanning electron microscopy revealed detailed structures, interpreted as meningeal fabrics, blood vessels (including capillaries) and potentially superficial cortical tissues, which have been replaced by calcium phosphate or molded by microcrystalline iron carbonate,” the paleontologists explained.

“The organism from which this endocast originates has been referred to informally as Iguanodon. Two Iguanodon-like taxa are now recognized from the Lower Wealden outcrops of Valanginian age: Barilium dawsoni and Hypselospinus fittoni.”

“The dimensions of the new specimen indicate that it came from an individual with a body length of 13-16 feet (4-5 m) and could therefore originate from either Barilium (up to 26 feet, or 8 m, long) or Hypselospinus (up to 20 feet, or 6 m, long).”

A time sequence outlining the inferred taphonomic history of the iguanodontian endocast from Bexhill. Scale bar – 10 mm. Image credit: Martin D. Brasier et al.

According to the team, the reason this 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 shortly after its death.

This allowed the soft tissues to become mineralized before they decayed away completely, so that they could be preserved.

“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,” said co-author Dr. David Norman, from the University of Cambridge.

“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.”

Scanning electron microscopy images of tubular structures on the exterior of the Bexhill endocast and within the outer laminar layer, interpreted as meningeal blood vessels. Arrows in (a) point to areas where the hollow nature of the vessels can be seen; arrows in (b) point to branching of the vessels; (c-f) additional images of hollow tubular structures within the outer laminar layer. Image credit: Martin D. Brasier et al.

In typical reptiles, the brain has the shape of a sausage, surrounded by a dense region of blood vessels and thin-walled vascular chambers (sinuses) that serve as a blood drainage system. The brain itself only takes up about half of the space within the cranial cavity.

In contrast, the tissue in the fossilized brain appears to have been pressed directly against the skull, raising the possibility that some dinosaurs had large brains which filled much more of the cranial cavity.

However, the team cautions against drawing any conclusions about the intelligence of dinosaurs from this particular fossil, and says that it is most likely that during death and burial the head of this dinosaur became overturned, so that as the brain decayed, gravity caused it to collapse and become pressed against the bony roof of the cavity.