Fossil teeth unearthed in Ethiopia suggest two distinct human ancestor species lived alongside each other between 2.6 and 2.8 million years ago, reshaping what is known about our evolution.
The 13 teeth come from a Homo species that lived in Ethiopia’s Afar region, overlapping with the hominin ancestor Australopithecus.
The teeth, found at the Ledi-Geraru archaeological site, reveal that the oldest members of the Homo genus coexisted with the Australopithecus.
“These specimens suggest that Australopithecus and early Homo coexisted as two non-robust lineages in the Afar region before 2.5 million years ago,” researchers said, “and that the hominin fossil record is more diverse than previously known.”
According to Kaye Reed, a co-author of the study, the discovery shifts our perception of human evolution.
“Here we have two hominin species that are together. And human evolution is not linear, it is a bushy tree, there are lifeforms that go extinct,” Dr Reed explained.
“This new research shows the image many of us have in our minds of an ape to a Neanderthal to a modern [human] is not correct. Evolution doesn’t work like that.”
Analysis of the teeth, published in the journal Nature, shows they belonged to a new Homo species rather than Australopithecus afarensis – represented by the famous “Lucy” specimen – which last appeared 2.95 million years ago.
“The new finds of Homo teeth from 2.6 to 2.8 million-year-old sediments confirm the antiquity of our lineage,” Brian Villmoare, lead author of the study, said.
The newly discovered ancestor species does not have a name yet. More fossils are needed for that to happen.
Researchers dated the specimen based on the fossil site’s volcanic and tectonic activity.
The region is home to many volcanoes that spew ash containing crystals called feldspars.
“We can date the eruptions that were happening on the landscape when they are deposited,” Christopher Campisano, another author of the study, explained, referring to feldspars. “And we know that these fossils are interbed between those eruptions, so we can date units above and below the fossils. We’re dating the volcanic ash of the eruptions that were happening while they were on the landscape.”
Examining the fossils and the landscape together allowed researchers to recreate the environment millions of years ago.
They found that the landscape traversed by these ancient human ancestors 2.6 to 2.8 million years ago was a stark contrast to modern times.
Back then, rivers flowed through a vegetated landscape into shallow lakes that expanded and contracted over time.
“The geology gives us the age and characteristics of the sedimentary deposits containing the fossils,” said another study author Ramon Arrowsmith. “It is essential for age control.”
It remains unclear if the Lucy species and the Australopithecus species ate the same things and competed with each other for food.
In further studies, researchers hope to examine the tooth enamel of the species to find out what they ate.
