Parks and Wildlife's Exmouth district manager Arvid Hogstrom said his office learnt of the theft of the 8-10cm, sharply serrated megalodon tooth from the Cape Range National Park in the Pilbara region on Friday but don't know when it was stolen as staff don't go to the site regularly.

Plans were underway to preserve and protect the fossil at the site, which had been hidden with vegetation and rocks, Mr Hogstrom said.

The tooth, which is at least 1.6 million years old, wasn't well known about, but must have been extracted from the rugged rock by someone in the know.

The thief may be a fossil collector, seeking to trade it on the black market, even though it's not particularly valuable, or perhaps just thought it would look good on their mantelpiece, Mr Hogstrom said.

"Not even all our staff knew where it was or even existed. But obviously word gets around. How it got back to the person who took it, we just don't know," he told AAP on Tuesday.

"There's definitely got to have been some information passed on."

Mr Hogstrom said he hoped whoever took the tooth - which came from a megalodon some 10 to 15 metres long - had a pang of guilt and returned it intact.

"We're hoping someone might come across it or hear about it ... we're just keen to have it back and have it in the community and in the public rather than just in someone's personal collection," he said.

"We encourage people to get in touch if they've got any ideas whatsoever."

Australian Associated Press