Scientists said on Wednesday a sophisticated new dating technique shows that Little Foot, an important fossil of an early human forerunner unearthed in the 1990s in South Africa, is roughly 3.7 million years old.

"The age of Little Foot has been highly debated," said geologist Darryl Granger of Purdue University in Indiana, whose research appears in the journal Nature.

The study's co-authors included Ryan Gibbon, an assistant professor at University of New Brunswick who helped date the fossil as a postdoctoral research in Granger's lab.

Stephen Motsumi, Laurent Bruxelles and Ron Clarke work in the Silberberg Grotto at Sterkfontein, where 'Little Foot' was found. (Francis Duranthon)

Some previous studies had suggested Little Foot could have lived as recently as 2.2 million years ago.

But the new study suggests Little Foot, a member of the species Australopithecus prometheus, lived at roughly the same time as Australopithecus afarensis, the species whose most famous fossil, known as Lucy, comes from Ethiopia. Both species blended ape-like and human-like traits but with different features.

The researchers analyzed 11 rock samples from around the nearly complete Little Foot fossil skeleton from the Sterkfontein Caves to gauge its age.

The findings may have important implications about the evolutionary relationships among humankind's ancient relatives.

Our species, Homo sapiens, appeared roughly 200,000 years ago. Earlier members of the human genus, Homo, date back more than 2 million years. Our genus was predated by other species on the human family tree including various representatives of the genus Australopithecus.

Members of Lucy's species were contemporaries of Little Foot, although Lucy herself lived about 500,000 years later.

Bigger and taller than Lucy

Like Lucy, Little Foot was female. The species was much bigger and taller than Lucy's, with gorilla-like facial features but fully upright and very strong with powerful hands for climbing, according to paleoanthropologists Ron Clarke and Kathy Kuman of the University of the Witwatersrand in Johannesburg.

Its hands were proportioned like ours, with a long thumb and relatively short fingers and palm, unlike the elongated hands of modern apes. Its legs were slightly longer than its arms, unlike modern apes.

The earliest stone tools found in the same cave date to around 2.18 million years ago, a similar age to tools from nearby sites. (Kathleen Kuman/Wits University)

Clarke and Kuman noted similarities in facial structure and some teeth between Little Foot and the later human relative Paranthropus, indicating Little Foot's species may have been ancestral to Paranthropus or a close cousin.

The new date for Little Foot indicates Lucy's species was not the only one that could have given rise to later members of the human family tree, Clarke and Kuman said.

"The fact, therefore, that we have at least two (Australopithecus) species living at the same time in different parts of Africa, (about) 3.67 million years ago, raises the question of how many other species there may have been which have not yet been discovered," Clarke and Kuman said by email.