Researchers from The University of Western Australia have helped British scientists confirm that an unassuming brown pebble, found more than a decade ago by a fossil hunter in Sussex, is the first example of fossilised brain tissue from a dinosaur.
The fossil, most likely from a species closely related to Iguanodon, displays distinct similarities to the brains of modern-day crocodiles and birds. Meninges – the tough tissues surrounding the brain – as well as tiny capillaries and portions of adjacent cortical tissues have been preserved as mineralised “ghosts”.
Dr Dave Wacey, from UWA’s Centre for Microscopy, Characterisation and Analysis (CMCA), used scanning electron microscope (SEM) techniques to identify the tough membranes, or meninges, which surround the 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 structure of the fossilised brain, and in particular that of the meninges, shows similarities with the brains of modern-day descendants of dinosaurs, such as birds and crocodiles.
“Usually one needs to apply a conductive coating (something like carbon or gold) to insulating material such as rock in order to remove charging artefacts when imaging in an SEM – but with this unique sample we were clearly not allowed to coat it,” Dr Wacey said.
“Instead, I used a modified type of instrument called an environmental scanning electron microscope (ESEM); this has special detectors which don’t require a vacuum to operate. So gas can remain in the analysis chamber and the conductivity of this gas overcame the charging effects from the non-conductive dinosaur brain sample.”
The research was partly funded by an Australian Research Council grant to CMCA, as well as a Future Fellowship grant to Dr Wacey.
The results are reported in a Special Publication of the Geological Society of London, published in tribute to Professor Martin Brasier of the University of Oxford, who died in 2014. Professor Brasier and Dr David Norman from the University of Cambridge coordinated the research into this particular fossil during the years before Professor Brasier’s untimely death in a road traffic accident.
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 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. This allowed the soft tissues to become mineralised 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,” Dr Norman said.
“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.”
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 fossilised 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 researchers caution against drawing any conclusions about the intelligence of dinosaurs from this particular fossil, and say 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.
“As we can’t see the lobes of the brain itself, we can’t say for sure how big this dinosaur’s brain was,” Dr Norman said.
“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. What’s truly remarkable is that conditions were just right in order to allow preservation of the brain tissue – hopefully this is the first of many such discoveries.”