When Jamie Hiscocks, an amateur fossil collector, picked up a brown pebble with unusual markings on a beach near Bexhill, Sussex in 2004, he could not have known the impact his discovery was about to have on the palaeontological community.
A study published in October revealed this to be the first example of a fossilised dinosaur brain. The authors describe the sample, aged at 133 million years old, as a “naturally occurring brain endocast of an iguanodotian dinosaur”; that is, an internal cast of part of the skull of a dinosaur related to the Iguanodon.
Dr Alex Liu, co-author of the paper, described the remarkably detailed features preserved in the specimen: “What we found were very fine detailed bundles of what seemed to be collagenous fibres, which you would expect in the outer protective tissues of the brain, and these are interspersed with open tubes that branch and run around the edges of the specimen, and these seem to be the capillaries.” It is incredibly rare for any soft tissue to be preserved at all: “the most striking thing is that something as delicate as brain tissue, and which you wouldn’t expect to ever see, has been preserved,” Dr Liu commented.
This is not the first example of a fossilised brain. One from a 300-million-year-old relative of the shark was discovered in Kansas in 2009. It is, however, the first from a land-dwelling vertebrate. The dinosaur brain tissue was preserved “through a process of ‘pickling’ and then mineral replacement,” says Dr David Norman of the University of Cambridge, another co-author on the paper: “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.”
Analysis of the specimen has revealed some unexpected features. Although the brain seems to be similar in structure to those of modern archosaurs (birds and crocodilians), it also appears to be much larger than expected. The typical archosaur brain is surrounded by a thick membranous layer, meaning the brain itself takes up only around half of the brain cavity.
In the sample this layer is incredibly thin, leading the researchers to believe that the brain was therefore much larger.
Dr Norman has an alternative suggestion. He believes this could have resulted from compression, due to the dinosaur being buried upside down.
“Of course, it’s entirely possible that dinosaurs had bigger brains than we give them credit for, but we can’t tell from this specimen alone.”