A giant tooth from a gargantuan shark that used to cruise the world's oceans 2 million years ago could be one of the oldest objects ever to be stolen by a thief.

The location of the ancient tooth inside a world heritage area in Western Australia was a tightly guarded secret, until it was discovered missing last Friday.

Parks and Wildlife manager Arvid Hogstrom said trying to work out why someone would steal it was the "million-dollar question" facing wildlife rangers and police.

Hogstrom told nine.com.au it was "hugely disappointing" to have lost such a significant and unique fossil from the Old Stone Age (Paleolithic era).

The tooth from the Megalodon, a fearsome predator that could grow 18m-long and weigh 100-tonnes, was in excellent condition.

Park rangers had previously hidden the tooth under a cover and rocks. Picture: Department of Biodiversity, Conservation and Attractions

Cape Range National Park rangers had hidden the fossil under a special cover and then covered it with rocks. Only a handful of people were believed to be aware of its location.

"It was only lightly attached to the rock and that's why we hadn't made it public. We'd gone to efforts to conceal it while we figured out how we could protect it in the future," Hogstrom said.

"Probably with a little bit of levering and hammering with a chisel they would have been able to remove it in five or ten minutes without too much trouble."

Hogstrom said the culprit likely came from one of three scenarios.

"It could be an amateur collector who just wants to add to their personal fossil collection. It could be someone who doesn't really know what they have taken, they just saw a fossil in the rock and thought that would be a nice thing to have on their mantelpiece.

"Or I guess it could be going on to some international trader. But my understanding is that these things aren't all that uncommon and it's not worth a huge amount of money. I think it's more of a local collector who has decided to top up their collection."

A man stands in the five-foot mouth of a fossil shark jaw. The shark is called Carcharoles Megalodon and was large enough to swallow a small car. (Getty)

Hogstrom said the fossil could be priced at several thousand dollars.

The Cape Range National Park is home to a number of similar Megalodon tooth fossils known to the public, but those specimens were more deeply buried and entrenched firmly into the rock face.

Parks and Wildlife officials had been intending to case the stolen tooth in bulletproof glass or reinforced grating to allow visitors to see the fossil in-situ.

Hogstrom said he was holding out hope for the tooth's return but feared it was now gone for good.

"Someone might not understand what they have taken and give it back to us. But I wouldn't be putting money on it."

View from Yardie Creek in the Cape Range National Park in Western Australia. UNESCO gave world heritage status to Western Australia's Ningaloo Coast in 2011. (AAP)

Megalodon, which means "big tooth" in Greek, were the largest shark to ever patrol the oceans before becoming extinct around 1.6 million years ago.

Scientists from Zurich University theorised Megalodon became extinct due to a lack of prey and increased competition from predators.