A newly-discovered human relative is believed to have walked alongside "Lucy" about 3.5 million years ago, knocking down past theories that only one ancestor existed at any given point in history. 

Upper and lower jaw fossils from Afar Ethiopia revealed the existence of the new species Australopithecus deyiremeda, a hominid that lived along other well-known ancestors such as Lucy, or Australopithecus afarensis, the Cleveland Museum of Natural History reported.

The discovery of the species provides the most conclusive evidence that multiple early human ancestors lived at the same time over three million years ago. Australopithecus deyiremeda is set apart from Lucy by its jaw structure and the size of its teeth.

"The new species is yet another confirmation that Lucy's species, Australopithecus afarensis, was not the only potential human ancestor species that roamed in what is now the Afar region of Ethiopia during the middle Pliocene," said lead author and Woranso-Mille project team leader Yohannes, curator of physical anthropology at The Cleveland Museum of Natural History. "Current fossil evidence from the Woranso-Mille study area clearly shows that there were at least two, if not three, early human species living at the same time and in close geographic proximity."

In the past, scientists have argued that only one human-ancestor existed at any given point in history before three million years ago. Until the 20th century, the fossil record backed up this idea, but the discoveries of Australopithecus bahrelghazali from Chad and Kenyanthropus platyops from Kenya were shown to both have lived during the same approximate period as the Lucy species. Additionally, the discovery of a 3.4 million-year-old Burtele partial foot in 2012 also backed up the idea that ancient human ancestors cohabitated. The partial foot is yet to be linked to an exact species, but the discovery of Australopithecus deyiremeda confirms multiple species existed at the same time during this early point in history. 

"This new species from Ethiopia takes the ongoing debate on early hominin diversity to another level," Haile-Selassie said. "Some of our colleagues are going to be skeptical about this new species, which is not unusual. However, I think it is time that we look into the earlier phases of our evolution with an open mind and carefully examine the currently available fossil evidence rather than immediately dismissing the fossils that do not fit our long-held hypotheses."

The findings were published in a recent edition of the journal Nature.