One Time, Two Early Humans Coexisted

In a groundbreaking discovery in early human evolution, scientists revealed that, using the "Burtele Foot" and the "Lucy fossil," they identified two hominin species that coexisted at the same place and time.

Back in 1974, scientists discovered 40 percent of a single hominin skeleton known as Lucy at the Hadar site in Ethiopia, which rose to prominence as the most complete early human ancestor ever found. Many years later, in 2009, another "enigmatic" hominin foot, Burtele, was discovered nearby at the Afar Rift.

Though researchers understood that the two human remains did not belong to the same species, Burtele Foot remained unclassified until recently, when researchers unearthed more fossils that helped solve the mystery. Lucy had already been categorized as a separate hominin, A. afarensis.

In 2015, a team at Arizona State University announced yet another human ancestor, Australopithecus deyiremeda, to which it would turn out Burtele’s Foot also belonged. The evidence added up.

Researchers could then conclude that 3.5 million years ago, at a "poorly understood time in human evolution," according to Reuters, two different hominins lived alongside one another, though they did not walk alike.

A team from ASU recently unearthed a new set of fossils: 25 teeth and a jawbone. Based on what they gleaned from the new evidence, Burtele, composed of eight-foot bones once attached to a very early hominin species, A. deyiremeda, which possessed both ape-like and human-like traits, according to Reuters.

Now that researchers know that Burtele and Lucy were distinct species, the Woranso-Mille site has become significant as the only location in the world where scientists have identified the coexistence of two hominin species with distinct characteristics.

The Burtele Foot retained an opposable big toe, according to a press release by Arizona State University News, which would have assisted this early human in climbing, with longer, more flexible toes. When it walked on two legs, it most likely pushed off its second digit rather than the big toe as we modern humans do today. Lucy’s species, A. afarensis, was fully bipedal with an abducted big toe. Researchers gleaned that early humans walked differently.

"So what that means is that bipedality — walking on two legs — in these early human ancestors came in various forms. The whole idea of finding specimens like the Burtele Foot tells you that there were many ways of walking on two legs when on the ground; there was not just one way until later."

Isotope analysis, furthermore, if not surprisingly, showed that the two species did not dine alike either. "I think the biggest surprise was despite ... how diverse these early australopith (early hominin) species were — in their size, in their diet, in their locomotor repertoires and in their anatomy — [they] seem to be remarkably similar in the manner in which they grew up," said Haile-Selassie, director of the Institute of Human Origins and professor at the School of Human Evolution and Social Change at ASU.

Studying how these ancient ancestors moved and what they ate gives scientists insight into how different species lived together without one driving the other to extinction.

"If we don’t understand our past, we can’t fully understand the present or our future. What happened in the past, we see it happening today," he said.

"In a lot of ways, the climate change that we see today has happened so many times during the times of Lucy and A. deyiremeda. What we learn from that time could actually help us mitigate some of the worst outcomes of climate change today."