Made by bare feet in wet sand after a rainstorm, the prints are an important clue to a period with a scarce fossil record: 100,000 to 300,000 years ago, when modern humans emerged.
"These were made by a person who looked anatomically just like us," said Lee Berger, a palaeoanthropologist who announced the discovery at a news conference at the National Geographic Society in Washington, where a fibreglass cast of the footprints was displayed.
Mr Berger and David Roberts, a South African geologist who found the fossils nearly two years ago, referred to the person who made the prints as "she", based on the small size of the feet, but acknowledged that it could have been a small man or a child.
If the prints were made by a female, she could be the anthropological "Eve", a hypothetical woman who lived in Africa between 100,000 and 300,000 years ago and carried a type of DNA that is passed on only through females.
Eve is thought to be the common ancestor of modern human, and while Mr Berger said it was highly questionable that the prints were hers, he also said they were made at the right time and place to fit her profile.
Mr Roberts, of the South African Council for Geoscience, found the footprints in the rocky shore of the Langebaan Lagoon, 60 miles (97km) north of Cape Town. The chances of them surviving to this day were "millions to one", he said. To last this long, the footprints had to be quickly covered after being made, possibly by blowing sand, then buried for a long time to be preserved in rock, then eroded to the point where hardened sediment from the ancient dunes could be chipped away to reveal them again.
What he first saw was a ridge in the rock along the lagoon that showed where the ancient sand had been pushed aside by the side of the woman's foot; the actual footprint was filled with sand.
Mr Roberts was looking for footprints in the area because he had already found fossilized tracks of carnivores and rock fragments that had been worked on by hominids.
Only three other sets of hominid footprints have been found in Africa, and two of these came from more than a million years ago, too early for modern humans. The third set were dated about 30,000 years ago, a blink in the course of human evolution, Mr Berger said.
The Langebaan footprints were dated by studying the surrounding sediments and noting the fluctuations in sea level in the area over time, Mr Roberts said. The line of footprints stretches away from the shore into what used to be ancient sand dunes which are now buried under rock. Mr Berger said scientists plan to uncover those additional footprints.Reuse content