Two of the most famous hominids, Lucy and Little Foot, may have belonged to species that were contemporaries, according to a new dating analysis.
The study, published in Nature, found 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.
Researchers analysed the minerals from the South African cave in which Little Foot was found and estimate a burial date of around 3.67 million years ago – about 500,000 years earlier than Lucy herself is thought to have lived, but when members of her species existed.
The cave that bore the nearly complete skeleton of Little Foot contained several Australopithecus fossils. It has been difficult to date the specimens due to erosion and soil deposits in the cave as well as human workings of it.
The new dates reported by Darryl Granger and colleagues are calculated by measuring levels of radiogenic isotopes of aluminium and beryllium in the quartz that surrounded the skeleton; these isotopes are formed by cosmic-ray bombardment and act as clocks in the rocks.
As well as dating the skeleton of Little Foot, this technique enables the authors to date the earliest stone tools found.
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.
Our species, Homo sapiens, appeared only 200,000 years ago, although earlier members of the human genus, Homo, date back more than two million years.