Melbourne, April 21 (IANS): A giant fossilised whale tooth -- believed to be five million years old -- was washed ashore on an Australian beach.

Paleontologists believed the tooth, which is bigger than that of a Tyrannosaurus-rex, belonged to a close ancestral relative of the Livyatan melvillei, an ancient species of the Peruvian sperm whale that died out millions of years ago, Xinhua news agency reported on Thursday.

It is the first evidence that this carnivorous species, which could grow up to 18 metres long and weigh around 40 tonnes, lived outside of the Americas.

The scientific discovery was stumbled upon by a local man at Beaumaris Bay, a Melbourne beach where fossils have been found in the past.

"After I found the tooth I just sat down and stared at it in disbelief," Murray Orr, the Australian fossil enthusiast who found the 3 kg, 30 cm-long tooth, said, adding: "I knew this was an important find that needed to be shared with everyone."

In 2008, international paleontologists found a three-metre whale skull in southern Peru that had comparable tooth dimensions to the Australian find. They named the prehistoric species Livyatan melvillei in honour of Herman Melville, author of the 1851 mythical whale tale "Moby Dick".

Peruvian scientists dated the fossilised head to around 13 million years ago, while Australian researchers estimated their fossil was much younger.

"If we only had today's sperm whales to go on, we could not predict that just five million years ago there were giant predatory sperm whales with immense teeth that hunted other whales," Museum Victoria's senior curator of vertebrate paleontology Dr Erich Fitzgerald said.

"Most sperm whales for the past 20 million years have been of the whale-killing kind."

Similar to Moby Dick, the fictional white whale, the Australian species would have lurked in the sea attacking other whales as its main food source.

Modern sperm whales, however, are not cannibals and prey on squid and fish.