Foot Fossil Reveals Two Human Species Coexisted 3 Million Years Ago

A fossilized foot may be from a prehuman species distinct from Lucy, the famous human ancestor whose species was prominent 3 million to 4 million years ago, according to a new study. Two very different prehuman species coexisted at one point, according to researchers.

Paleontologists discovered the foot in a region of Ethiopia called Burtele in 2009, and said it resembles the foot of a prehuman that potentially lived over a million years earlier than Lucy. The foot's big toe is set apart from the rest of the foot and lacks an arch, making it ideal for gripping tree branches.

The Burtele partial foot clearly shows that at 3.4 million years ago, Lucy's species, which walked upright on two legs, was not the only [prehuman] species living in this region of Ethiopia, Dr. Yohannes Haile-Selassie, lead researcher and curator of physical anthropology at the Cleveland Museum of Natural History, said in a statement. Her species co-existed with close relatives who were more adept at climbing trees.

Upright walking had a profound impact on human bone structure - humans developed long big toes that are in line with our other toes, a strong heel, and an arch to help distribute weight as humans began walking upright. This finding sheds light onto the evolution of the human foot, researchers said.

Once walking on two legs - bipedality - evolved, we didn't think there was another species that had the capability to climb up trees living at the same time, Haile-Selassie told the Guardian. We never expected another related species running around with the capability to climb up trees.

The foot possibly belongs to a new species of human, but researchers are holding off on saying so until they find other bones such as a skull or teeth.

I think it probably does represent a new species, but until we find more evidence, we're being cautious about it, Dr. Bruce Latimer, study coauthor and professor of anthropology at Case Western Reserve University, told the Guardian.

In an accompanying article, Daniel Lieberman, an evolutionary biologist at Harvard University, said that more information is needed to determine what kind of body went with the foot. More fossils would help scientists determine what featured evolved when. Some features, such as upright walking, may have evolved multiple times.

Human evolution is often portrayed as a triumph of bipedalism, but who among us has not occasionally regretted our species' comparative clumsiness in the trees? Lieberman wrote. I, for one, am pleased to know that some [prehumans] retained feet well adapted for [tree climbing] millions of years after we started to walk.

Donald Johanson, who discovered Lucy in 1974, called the find one of those fascinating evolutionary experiments that tried walking but never fully committed.

It didn't seem to want to make up its mind whether it wants to live in the trees or on the ground, Johanson told the Associated Press.

The journal Nature published the study on Wednesday.