Lucy, the most complete skeleton of a human ancestor found, was not alone millions of years ago, suggests a study published on June 6 in the journal Proceedings of the National Academy of Sciences. It turns out that there were other early human species that lived during our oldest ancestor’s time, within the middle Pliocene period between 3.8 and 3.3 million years ago.

The researchers from the Cleveland Museum of Natural History and Max Planck Institute for Evolutionary Anthropology in Germany explain that Australopithecus afarensis, the species which Lucy belonged to, was believed to have given rise to another hominin species. However, this linear evolution idea was disputed upon the discoveries of Australopithecus bahrelghazali in Chad in 1995 and Kenyanthropus platyops in Kenya in 2001.

Nevertheless, many scientists argued that both the Chadian and Kenyan fossils were merely geographical variants of the Australopithecus afarensis species rather than unique hominins. In 2015, a new species called Australopithecus deyiremeda was identified in the fossil-rich site of Woranso-Mille in Ethiopia.


The left half of the lower jaw of Australopithecus deyiremeda (BRT-VP-3/14), a 3.5 to 3.3 million-year-old human ancestor species discovered by the Woranso-Mille project. Credit: Yohannes Haile-Selassie

Still, all of these were simply assumed to have existed long after Lucy’s species was gone. But the latest fossil analysis reveals that these species lived alongside each other. Now, the question remains about the relationship of these human ancestors, how they shared resources or how they generally co-existed.

“These new fossil discoveries from Woranso-Mille are bringing forth avenues of research that we have not considered before,” adds Denise Su, The Cleveland Museum of Natural History’s curator of paleoecology and paleobotany. “How did multiple closely related species manage to co-exist in a relatively small area? How did they partition the available resources? These new discoveries keep expanding our knowledge and, at the same time, raise more questions about human origins.”

Nevertheless, while the identity of the other hominin species has been known, their fossils remain incomplete. Max Planck Institute for Evolutionary Anthropology’s Stephanie Melillo asserts that more fossils are still needed to clarify the mystery behind human ancestry.