The skull was obtained by the Columbus Avenue shop Maxilla and Mandible Ltd in March from a mysterious man who claimed to represent the estate of a collector. The shop's owner Henry Galiano realised it could be ancient and valuable and called in experts from the nearby American Museum of Natural History.

The grey-coloured skull, a nearly complete cranium but missing an upper and lower jaw, is probably that of a male Homo erectus in his 20s who walked the earth between 1.7 million and 300,000 years ago, scientists have concluded. The fossil is believed to have come originally from Indonesia.

"It's a very interesting specimen because it's not like any other Homo erectus we know from Indonesia or anywhere else," said Dr Eric Delson, a paleoanthropologist at Lehman College of the City University of New York who led the investigation.

Although the skull's brain size appears to be within range for Homo erectus - about half the size of a modern human's brain - its forehead is high like a Homo sapien and not sloping like an earlier hominids. The inside surface of the skull also shows the brain had some similar features to that of Homo sapiens suggesting a potential for speech.

"Of course, it's only one individual, but it could represent a distinctive population. We just don't know," Delson told the New York Times.

The skull, which could have fetched as much as $500,000 on the open market, has been returned to Indonesia.