Melbourne's prehistoric answer to Moby Dick has been uncovered with a five-million-year-old killer whale tooth found at a renowned fossil site.

A fossil enthusiast discovered the 30cm tooth – the largest ever found in Australia – belonging to a giant predatory sperm whale with immense teeth said to have been used to hunt other whales.

Museum Victoria senior curator Dr Erich Fitzgerald is delighted the prehistoric killer whale fossil has been donated to the museum. Picture: Museum Victoria More

“After I found the tooth I just sat down and stared at it in disbelief. I knew this was an important find that needed to be shared with everyone,” said Murray Orr, who made the discovery at Beaumaris Bay, in Melbourne’s south east.

The prehistoric artifact is believed to belong to an extinct species of killer sperm whale from the Pliocene epoch, measuring up to 18 metres long and weighing 40,000 kilograms.

The tooth is larger than those of a living sperm whale and even exceeds the dental dimensions of the mighty Tyrannosaurus Rex.