Western Australian park rangers have all but given up hope the thief who stole the valuable tooth of a gargantuan shark which once cruised the world's oceans 2 million years ago will return it.

The location of the fossilised Megalodon tooth had been a tightly-guarded secret, believed known only by a handful of people, until it was discovered missing from a WA world heritage park in March.

Arvid Hogstrom, from WA's Parks and Wildlife Service, estimated the unique fossil from the Old Stone Age (Paleolithic era) was between 2 and 2.5 million years old.

"It is a big loss, it was such a great specimen," Hogstrom told Nine.com.au .

A thief had likely chiselled the tooth free from its ancient resting place in less than 15 minutes, Hogstrom believed.

Following the theft, Hogstrom's team had pinned their hopes on the local community identifying the culprit, who may not have been aware of the tooth's importance.

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

"There's always the chance somebody might get a case of the guilts later on," Hogstrom said.

"Someone might also notice the tooth sitting on a friend's mantelpiece and query where they got it from.

"I think we can say it is probably lost but we live in hope"

The 10cm-long tooth in the Ningaloo Coast World Heritage Area had come from the mouth of a Megalodon shark, a fearsome predator that could grow 18-metres long and weigh 100-tonnes.

Cape Range National Park is home to a number of similar Megalodon tooth fossils known to the public, but those specimens are more deeply buried and entrenched in earth.

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)

Before it was stolen, Parks and Wildlife officials had intended to case the now missing tooth in bulletproof glass or reinforced grating to allow visitors to see the fossil in-situ.

"A lot of local people expressed their dismay after the tooth disappeared," Hogstrom said

"Word got around the community but it didn't result in any direct clues or the item being handed back."