It seems that "Lucy" was not the only hominin on the block in northern Africa about 3 million years ago.
A team of researchers that included Johns Hopkins University geologist Naomi Levin has announced the discovery of a partial foot skeleton with characteristics (such as an opposable big toe bone) that don't match those of Lucy, the human ancestor (or hominin) known to inhabit that region and considered by many to be the ancestor of all modern humans.
The discovery is important because it provides first-ever evidence that at least two pre-human ancestors lived between 3 million and 4 million years ago in the Afar region of Ethiopia, and that they had different ways of moving around the landscape.
"The foot belonged to a hominin species -- not yet named -- that overlaps in age with Lucy (Australopithecus afarensis). Although it was found in a neighboring project area that is relatively close to the Lucy fossil site, it does not look like an A. afarensis foot," explains Levin, an assistant professor in the Morton K. Blaustein Department of Earth and Planetary Sciences in the Krieger School of Arts and Sciences.
A paper in the March 29 issue of Nature describes this foot, which is similar in some ways to the remains of another hominin fossil, called Ardipithecus ramidus, but which has different features.
Its discovery could shed light on how our ancestors learned to walk upright, according to Levin.
"What is clear is that the foot of the Burtele hominin was able to grasp items much better than its contemporary, A. afarensis, would have been able to do, which suggests that it was adept at moving around in trees," says Levin, who was part of a team led by Yohannes Haile-Selassie of the Cleveland Museum of Natural History that also included researchers from Case Western Reserve University and the Berkeley Geochronology Center.
The finding is important, Levin says, because it shows that there is much more to learn about the role of locomotion in human evolution.
"This fossil makes the story of locomotion more complex, and it shows that we have a lot more to learn about how humans transitioned from moving around in trees to moving around on the ground -- on two legs.This fossil shows that some hominins may have been capable of doing both," she says.
The fossil, dated to approximately 3.4 million years ago, was discovered in 2009 in sediments along the Burtele drainage in the Afar region of Ethiopia that is now very hot and dry. The researchers believe the area was wetter and more wooded when the Burtele hominin lived, based on its deltaic sedimentary context, results from isotopic studies and the range of fossil animals found near the site.
"We're just at the beginning of understanding the environmental context for this important fossil. It will be a critical part of understanding this hominin, its habitat and the role that the environment played in its evolution," she says.
- Yohannes Haile-Selassie, Beverly Z. Saylor, Alan Deino, Naomi E. Levin, Mulugeta Alene, Bruce M. Latimer. A new hominin foot from Ethiopia shows multiple Pliocene bipedal adaptations. Nature, 2012; 483 (7391): 565 DOI: 10.1038/nature10922
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