Prehistoric footprints of a woman carrying a toddler while dodging sabre-toothed cats and giant sloths are the longest set of fossilised human prints ever found, scientists have said.
The prints, which stretch for almost a mile and were discovered in the White Sands National Park in New Mexico, USA, date back 13,000 years.
Prior to their discovery, the longest track, located in Northern Tanzania, was only around 200 metres long, said Professor Matthew Bennett, of the University of Bournemouth.
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Scientists say the newly-discovered track, and the story it reveals, could go on even further into the wilderness â€“ but a US military missile range neighbouring the park means they are unable to follow the trail to its end.
"We just don't know how far they went," said Prof Bennett, the co-author of a study of the trail, published in the Quaternary Science Reviews. "It would be really nice in the future, perhaps if we have access to the ranges, to trace it further."
Locally known as "ghost tracks" because they can only be seen under certain weather conditions, the adult tracks were first discovered in 2017, followed by the child's.
The prints tell the remarkable story of a woman and a small child as they made their way across the mudflats with large predators crossing their path.
An analysis found the woman was moving at a rapid pace, intermittently carrying and putting down the child.
On the outward journey, her prints show that she was slipping, suggesting conditions were wet and treacherous. But on her return, following the same path almost exactly, she was alone and no slipping marks were detected.
During the trips, other tracks show a giant sloth, mammoths and sabre-tooth cats crossed their path, and the sloth was startled by their scent.
"As the animal approached the trackway, it appears to have reared up on its hind legs to catch the scent, pausing by turning and trampling the human tracks before dropping to all fours and making off," Prof Bennett said.
In contrast, the mammoth tracks cross those of the humans without deviation.
The path was discovered just a few centimetres under the surface of a dry lake bed, known as playa, which would have been muddy at the time.
After being baked by the sun and covered over slightly by drifting material, the tracks have stayed near the surface of the lake for over 10,000 years, said Prof Bennett.
"It's absolutely unbelievable," he added. "When you look at the tracks, it looks a bit as if you just stepped out of the shower and you're making wet footprints on the bathroom. But how long they will last into the future we don't know, because the conditions are changing there with environmental change."
The story of the struggle of the woman and child is one of both scientific evidence and poetry, he said.
"There's a boundary in science between pure evidence and poetry and we're on that boundary, but everything that we said in the story is evidenced in some shape," he added.
"Here, we can actually track the individuals across the landscape over huge distances which you can do at no other site, and that's what's so amazingly fascinating."