The dinosaur's 10-inch-long claws likely made up for its fairly delicate jaws and small teeth, and helped it hunt, researchers said.
"They didn't have skulls like T rex, which could crush bones with their incredible bite," said lead researcher Phil Bell, a lecturer of paleontology at the University of New England in Australia.
"Instead, they probably used their hands and massive claws - a bit like a raptor - to bring down their prey," Bell told 'Live Science'.
Miners discovered and excavated the partial skeleton in the 1990s in the opal fields in Australia.
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The miners may have missed or destroyed some of the fossils, and fresh breaks on the bones suggest they were damaged during excavation, the researchers said.
Still, the finding is the second most-complete skeleton of a theropod (a group of bipedal, mostly meat-eating dinosaurs) from Australia, Bell said.
The researchers have not named the new species yet primarily because the skeleton is incomplete. They are, however, calling it "lightning claw" for now in honour of its location and impressively sized claws.
Researchers have found other remains of megaraptorids in South America and Australia.
Lightning claw predates the oldest known megaraptorid found in Australia (Australovenator) by 10 million years.
The findings were published in the journal Gondwana Research.