A fossil discovered on a beach has been confirmed as the earliest known creature to live on dry land.

The fossilised millipede, which is less than half an inch long, was found a year ago on the shore at Cowie Harbour near Stonehaven, a fishing town south of Aberdeen.

Scientists say it is about 420 million years old, some 20 million years older than what had previously been believed to be the oldest breathing animal - a spider-like creature chiselled out of the chert, a type of rock, at Rhynie, also in Aberdeenshire.

The millipede was discovered by an amateur fossil collector and has been named Pneumodesmus by researchers at Yale University and the National Museums of Scotland. Their results have been published in the American Journal of Palaeontology.

Dr Lyall Anderson, curator of invertebrate palaeontology at the National Museums, told the Sunday Herald newspaper: "It was obvious to me this was the oldest example of this group of animals that has ever been found."

The site near Stonehaven is well known for its arthropods - spidery animals such as sea scorpions. However, those are aquatic animals while the Pneumodesmus is air-breathing. Dr Anderson said: "The fact this has got very well- developed structures to breathe air suggests there must have been things prior to that which these developed from, so we should be looking further back in time to see if this thing had ancestors."