CNN — 

A scan of the skull of a 319-million-year-old fossilized fish has led to the discovery of the oldest example of a well-preserved vertebrate brain, shining a new light on the early evolution of bony fish.

The fossil of the skull belonging to the extinct Coccocephalus wildi was found in a coal mine in England more than a century ago, according to researchers of the study published in the journal Nature on Wednesday.

The fossil is the only known specimen of the fish species so scientists from the University of Michigan in the US and the University of Birmingham in the UK used the nondestructive imaging technique of computed tomography (CT) scanning to look inside its skull and examine its internal bodily structure.

Upon doing so, came a surprise. The CT image showed an “unidentified blob,” a University of Michigan press release said.

The distinct, 3D object had a clearly defined structure with features found in vertebrate brains: It was bilaterally symmetrical, contained hollow spaces similar in appearance to ventricles and had extending filaments that resembled cranial nerves.

“This is such an exciting and unanticipated find,” study coauthor Sam Giles, a vertebrate paleontologist and senior research fellow at the University of Birmingham, told CNN Thursday, adding that they had “no idea” there was a brain inside when they decided to study the skull.

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“It was so unexpected that it took us a while to be certain that it actually was a brain. Aside from being just a preservational curiosity, the anatomy of the brain in this fossil has big implications for our understanding of brain evolution in fishes,” she added.