Ancient crocodiles longer than a Volkswagen Beetle once ran on two legs through parts of what is now South Korea.
The discovery was made by an international research team, including Australian scientists, who analysed fossilised footprints dating from 110-120 million years ago.
The footprints were initially thought to belong to an ancient flying reptile called a pterosaur, the ancestor of modern birds.
But researchers now say they belong to three-metre long crocodiles that walked on hind legs as tall as the average adult human, creating footprints some 24cm long.
"At one site, the footprints were initially thought to be made by a giant bipedal pterosaur walking on the mudflat," University of Queensland palaeontologist and research co-author Dr Anthony Romilio said.
"We now understand that these were bipedal crocodile prints.
"And while footprints were everywhere on the site, there were no handprints."
The research team, led by Professor Kyung Soo Kim from Chinju National University of Education, soon realised why.
"Typical crocodiles walk in a squat stance and create trackways that are wide," Professor Kim said.
"Oddly, our trackways are very narrow looking - more like a crocodile balancing on a tight-rope.
"When combined with the lack of any tail-drag marks, it became clear that these creatures were moving bipedally.
"They were moving in the same way as many dinosaurs, but the footprints were not made by dinosaurs."
Dr Romilio said fossil crocodile tracks were quite rare in Asia.
"So finding an abundance of nearly one hundred footprints was extraordinary," he said.
"They even have the fine details of the toe-pads and scales on their soles preserved."
The discovery was published in the journal Scientific Reports.