LONDON – British archaeologists have unearthed an ancient skull carrying a startling surprise — an unusually well-preserved brain. Scientists said Friday that the mass of gray matter was more than 2,000 years old — the oldest ever discovered in Britain. One expert unconnected with the find called it "a real freak of preservation."

The skull was severed from its owner sometime before the Roman invasion of Britain and found in a muddy pit during a dig at the University of York in northern England this fall, according to Richard Hall, a director of York Archaeological Trust.

Finds officer Rachel Cubbitt realized the skull might contain a brain when she felt something move inside the cranium as she was cleaning it, Hall said. She looked through the skull's base and spotted an unusual yellow substance inside. Scans at York Hospital confirmed the presence of brain tissue.

Hall said it was unclear just how much of the brain had survived, saying the tissue had apparently contracted over the years. Parts of the brain have been tentatively identified, but more research was needed, he said.

He said it was a mystery why the skull was buried separately from its body, suggesting human sacrifice and ritual burial as possible explanations.

The existence of a brain where no other soft tissues have survived is extremely rare, according to Sonia O'Connor, an archaeological researcher at the University of Bradford in northern England who helped authenticate the discovery.

"This brain is particularly exciting because it is very well preserved, even though it is the oldest recorded find of this type in the U.K., and one of the earliest worldwide," she said.

The old brain is unlikely to yield new neurological insights because human brains aren't thought to have changed much over the past 2,000 years, according to Chris Gosden, a professor of archaeology at Oxford University unconnected with the find.

He confirmed it was the oldest brain found in Britain. He noted that far older preserved brains, thought to be approximately 8,000 years old, were found in 1986 when dozens of intact human skulls were uncovered buried in a peat bog in Windover Farms in Florida.

"It's a real freak of preservation to have a brain and nothing else," Gosden said. "The fact that there's any brain there at all is quite amazing."

Hall said the brain found at York University was being kept in its skull in an environmentally controlled storage facility for further study.