A rusty-brown rock found on a beach by a fossil hunter might contain a bit of preserved dinosaur brain.
If so, it would be the first time scientists have ever found fossilized brain tissue from a dinosaur.
The fossil comes from a species closely related to Iguanodon, a large herbivore that lived about 130 million years ago. A collector named Jamie Hiscocks found it in 2004, near Bexhill in the United Kingdom.
"He picked it up and noticed that it was slightly unusual in its shape and its texture," says Alex Liu of the University of Cambridge. "There's a series of bumps to this specimen that are quite characteristic of it fitting into the brain case of a dinosaur."
This kind of fossil gets made when sediment fills up a dinosaur's skull cavity and hardens. Later, if the skull breaks off and disappears, what's left behind is a solid object that reveals the shape of the skull's inner cavity.
What's different about this particular example, Liu says, is that the outer millimeter or so of this fossil "is actually mineralization of some of the soft tissue structures that were preserved before they decayed away within the original dinosaur brain case."
The dead dinosaur's head may have fallen into a bog or a swamp, he says, where chemical conditions allowed the soft tissues to become mineralized.
Hiscocks showed his unusual fossil to Martin Brasier of the University of Oxford, who was the first to recognize that it might contain preserved brain tissue. A team of researchers examined the sample in detail and found what they believe are tough collagen fibers and tiny blood vessels that are part of the protective outer covering of the brain.
Lower down, they see hints of another textured surface that might be the actual top of the brain itself. "It's a little bit harder to convince yourself that it's definitely there," Liu says, "just because it is deeper within the specimen so it's harder to see it on the surface. But we think that we have actually got some of that tissue preserved, as well."
One member of the research team is describing the find Thursday at the annual meeting of the Society of Vertebrate Paleontology in Salt Lake City. A full report appears in a special publication of the Geological Society of London that's a tribute to Brasier, who died in 2014 before he was able to publish on this find.
Any claim of preserved soft tissue from a dinosaur tends to be controversial, and the idea that scientists might have part of an actual brain is going to get a lot of scrutiny.
"That's a remarkable claim, just because brain tissue turns out to be one of the first things that decomposes after an animal dies," says Lawrence Witmer of Ohio University, a paleontologist who studies the soft tissues of dinosaur heads.
He thinks the scientists make a "compelling case" that they have part of the protective outer covering of the brain.
"What's potentially even more exciting is that they are very cautious, as good scientists are, about the possibility that they might even have some preservation of the neural tissue of the brain underneath," notes Witmer, who says this is a surprise. "We would never expect to see actual brain tissue preserved."
Witmer thinks the bar for evidence should be very high. "These are, in a sense, extraordinary claims," he says.
Amy Balanoff of the Center for Functional Anatomy and Evolution at Johns Hopkins University calls the find "intriguing." But she'd like to see comparisons to the anatomy of birds or crocodiles, and she wants to see more details on the branching pattern of the putative blood vessels.
"I'm not convinced," says Mark Norell of the American Museum of Natural History. He's concerned that the paper describing the find was published even though the fossil specimen is not yet in a public repository, such as a museum, where others can study it. What's more, he thinks the report generally doesn't reflect the state-of-the-art knowledge on dinosaur brain anatomy.
If the finding stands up to scrutiny, it's unclear what the discovery could reveal about dinosaurs' intellectual capacity.
In modern reptiles, Liu says, the brain does not take up the whole brain cavity. The brain is surrounded by a lot of protective, spongy tissue. But in this fossil, the brain's protective covering seems to be thin, suggesting that the brain was filling more of the cavity and the dinosaur could have had a greater mental capacity.
"Understanding of dinosaurs as a whole has changed completely in the last 20 or 30 years. Dinosaurs are now seen to be much more mobile, agile, smart creatures," Liu says, "and this is just one line of evidence that supports that view."
One thing that's almost certain is that scientists will now be going back and looking with new eyes at old fossils that are already in collections, according to Witmer.
"It's not like we didn't think dinosaurs had brains," Witmer says, but "if you don't know what you're looking for, you're not likely to find it."