Giant fossilized tooth signals cannibal killer sperm whales outside Americas (PHOTOS)

A huge 5 million-year-old tooth belonging to a killer sperm whale has been found in Australia, shaking up the theory that the extinct species only lived in the Americas.

The ancient tooth is the largest ever collected in Australia at 30cm long (12 inches) and was discovered at Beaumaris Bay near Melbourne by fossil enthusiast Murray Orr.

Orr spotted an object he thought was a discarded can, but quickly realized he had stumbled upon something much bigger – and much more interesting.

"As it was coming out, I thought it might be an anti-aircraft shell, I thought, 'Here we go, I'm going to blow my arm off,’” he told The Age.

The fossil is now in the hands of the Victoria Museum who say it is an internationally significant find and the first evidence of such a gigantic, whale hunting, sperm whale outside the Americas.

The tooth comes from the Pliocene Epoch era and represents a formidable predator that differs most from sperm whales of today in terms of their diet: this ancient whale feasted on smaller whales, while modern species live off squid and fish.

"If we only had today's deep-diving, squid-sucking sperm whales to go on, we could not predict that just 5 million years ago there were giant predatory sperm whales with immense teeth that hunted other whales," said Dr. Erich Fitzgerald, Senior Curator of Vertebrate Paleontology at the Victoria Museum.

The Beaumaris sperm whale had dental dimensions greater than a Tyrannosaurus Rex.

The tooth that was found, however, was missing both the tip of the crown and part of the root.

"It gets even more exciting though as this is the tooth of a whale which was not fully grown," Dr Fitzgerald said. "If the whale had lived longer it would have been bigger."

The gigantic whale may have measured up to 18m (59 feet) in length and weighed up to a colossal 40,000 kilograms (40 tons).