The "Little Foot" fossil discovered at Sterkfontein Caves in South Africa could help shed more light on mysteries regarding the lives of ancient human ancestors. The nearly complete skeleton was found in the 1990s, but the age of the fossil remained a question among paleontologists.
A new dating technique was used to show the artifact dates to around 3.7 million years ago, around the time of the famous fossil Lucy.
The fossil is likely a member of the species Australopithecus prometheus, while Lucy, discovered in Ethiopia, is the best-known example of Australopithecus afarensis. Each species featured both ape-like and human structures, although the two varieties of our ancestors differed significantly from each other.
Researchers studied 11 samples from the Little Foot fossil to accurately determine the age of the artifact. Instead of studying the bones directly, investigators examined the ratios of aluminum and beryllium isotopes in quartz crystals surrounding the artifact. Isotopes, chemical elements with differing numbers of neutrons, are formed by interactions with cosmic rays, allowing the atoms to be used for dating.
Homo sapiens evolved around 200,000 years ago, while our genus, Homo, dates back more than two million years in the fossil record. Australopithecus first walked the Earth around four million years before our own time.
Little Foot, also a female like Lucy, lived around 500,000 years before her fellow Australopithecus. Compared with afarensis, A. prometheus was stockier and possessed a greater physical strength, which could have aided the creatures in climbing. The fossil exhibits legs shorter than its arms, as well as relatively short fingers and palms, traits not shared by modern apes.
Teeth found in the fossil are similar to the human ancestor Paranthropus, suggesting the two species may have been closely related. This new study suggests that several other species may have also played roles in the evolution of the earliest human beings.
"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," Ron Clarke and Kathy Kuman of the University of the Witwatersrand in South Africa said.
Investigators believe the individual who formed the Little Foot fossil fell down a narrow shaft, leading to her death. Four foot bones of Little Foot were discovered in 1994, followed by discovery of her shin bone three years later. For years, anthropologists and biologists arguing about which species included Little Foot, as well when she lived.
"The original date we published was considered to be too old, and it wasn't well-received. However, dating the Little Foot fossil as 3.67 million years old actually falls within the margin of error we had for our original work. It turns out it was a good idea after all," Darryl Granger of Purdue University said.
Analysis and dating of the Little Foot fossil was published in the journal Nature.