Footprints left by ancient humans 800,000 years ago have been found in Britain, the earliest evidence of such markings outside Africa, scientists said Friday.
Researchers discovered the footprints, which were left by both adults and children, in ancient estuary mud at Happisburgh in Norfolk, eastern England.
The only older footprints found so far are at Laetoli in Tanzania, at about 3.5 million years old, and at Ileret and Koobi Fora in Kenya at about 1.5 million years, they added.
"This is an extraordinarily rare discovery," said Nick Ashton of the British Museum, who led the research team, which also involved the National History Museum and Queen Mary University London.
The discovery came at an archaelogical site that has yielded several previous discoveries of stone tools and fossil bones, including mammoth remains.
The researchers found the prints at low tide when waves washed away much of the beach sand to explose the silt below.
"At first we weren't sure what we were seeing but as we removed any remaining beach sand and sponged off the seawater, it was clear that the hollows resembled prints, perhaps human footprints, and that we needed to record the surface as quickly as possible before the sea eroded it away," Ashton said.
The group of early humans that left the footprints appeared to have consisted of at least one male and several smaller people believed to be females and youngsters, the researchers said.
"They are clearly a family group rather than a hunting party," said Ashton.
Analysis of the prints found that they were were from a "range of adult and juvenile foot sizes" equating to modern shoe sizes of up to British 7 or 8 (US 8 or 9, European 41 or 42).
The reearchers estimated that the height of the ancient humans who left the prints varied from about 0.9 metres to over 1.7 metres (2 ft 11 in to 5 ft 6 in), not far off the height of modern humans.
They were dated at 800,000 years old partly on the basis of the site's geological position beneath glacial deposits, but also because the fossils there come from now-extinct types of mammoth and horse and early forms of vole that were alive at that time.
But the question of exactly what type of ancient humans left their footprints in the sands of time remains a mystery.
They may have been related to people of a similar period in history found in Atapuerca in Spain, assigned to the species Homo antecessor, or Pioneer Man, said Chris Stringer of the Natural History Museum.
"These people were of a similar height to ourselves and were fully bipedal," he said.
Homo antecessor apparently became extinct in Europe 600,000 years ago and was perhaps replaced by the species Homo heidelbergensis, followed by the Neanderthals from about 400,000 years ago, and eventually modern humans some 40,000 years ago.