They're scary enough as it is but scientists have discovered crocodiles may have once walked on their hind legs.

Paleontologists in South Korea and Australia made the startling discovery while analysing fossilised footprints from more than 100 million years ago.

The researchers first thought the fossilised foot impressions were from another ancient reptile, known as the pterosaur.

But investigations revealed the footprints to have heel-to-toe impressions, which the palaeontologists believe were unlikely to have been made by the flying reptiles.

The lack of any tail-drag marks further reinforced the scientists' suspicions and it became clear the creatures once walked bipedally. Not only could they stand upright, they were about 3 metres long and could run like ostriches.

Source: 9News