A graduate student this month photographed what some thought was a remarkable find: A complete tusk of a prehistoric pygmy mammoth.

It turned out to be something far older.

A team of researchers spent two days on Santa Cruz Island excavating and determined it was a jawbone from an extinct whale species.

Lotus Vermeer of the Nature Conservancy says the bone was found in a rock formation estimated to be between 9.5 million to 25 million years old -- long before mammoths roamed the Channel Islands.

The team dug out the bone and cast it in plaster. The bone is about 3 feet (a meter) in length.

A number of other bones were found nearby that could be even older and may include an intact whale skull.

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