A duck-billed, three-foot long creature nearly twice as big as a modern platypus has been called Obdurodon tharalkooschild and probably wasn't a direct ancestor of the creatures we know today.
"It looks like modern platypus on steroids -- we'll have to call it platypus Godzilla," said Professor Mike Archer of the University of New South Wales. "It definitely had good teeth and was a very robust animal with a big brutish-looking snout."
"It pretty well blew our minds," he said. "We'd never seen anything this big so it really knocked our socks off to think that platypus could get this big."
The ancient platypus had teeth into adulthood, meaning it could chew small vertebrates like turtles and frogs. Modern platypus bruise their prey to death using pads in their bills.
While modern platypus are relatively timid, they have venomous barbs on their hind legs that contain venom strong enough to take a full-grown human out of commission for a few hours.
"If you scale that up to perhaps two or three times the amount of venom in an animal much larger than that, you suddenly start thinking about this animal as a predator," Archer said.
The discovery happened when when Rebecca Pian, a paleontology Ph.D. student, took a second look at a tooth, stashed in a cupboard at the university. It had come from Queensland, home to one of the richest fossil deposits in the world.
Pian, who is now studying at Columbia University in New York, said the molar wasn't something obviously remarkable.
"It was only when I started studying it that I realized it was really different from the others," she said. "It was a lot bigger and had some unique features.”
The discovery was published in the Journal of Vertebrate Paleontology.