Humans split away from gorillas about 10 million years ago - at least 2 million years earlier than previously thought, a new study has found.
A common ancestor of apes and humans, Chororapithecus abyssinicus, evolved in Africa, not Eurasia, researchers said.
"Our new research supports early divergence - 10 million years ago for the human-gorilla split and 8 million years ago for our split from chimpanzees," said Giday WoldeGabriel, geologist at Los Alamos National Laboratory in US.
"That's at least 2 million years earlier than previous estimates, which were based on genetic science that lacked fossil evidence," said WoldeGabriel.
"Our analysis of C abyssinicus fossils reveals the ape to be only 8 million years old, younger than previously thought. This is the time period when human and African ape lines were thought to have split, but no fossils from this period had been found until now," WoldeGabriel said.
Chimpanzees, gorillas, orangutans and humans compose the biological family Hominidae. Our knowledge of hominid evolution - that is, when and how humans evolved away from the great ape family tree - has significantly increased in recent years, aided by unearthed fossils from Ethiopia, including the C abyssinicus, a species of great ape.
Researchers characterised the volcanic ash and provided chemistry for local and regional correlation of the ashes sandwiching the fossils from Ethiopia's Chorora area, a region where copious volcanic eruptions and earthquakes entombed fossils recently uplifted via ground motion and erosion.
They recovered the fossil remains of at least eight hominid species, including some of the earliest hominids, spanning nearly 6 million years.
In the 1990s, researchers had discovered the nearly intact skeleton of the 4.4-million-year-old species Ardipithecus ramidus (nicknamed "Ardi") and its relative, the million-year-older species Ardipithecus kadabba.
These Ardipithecus fossils were the earliest ancestor of humans after they diverged from the main ape lineage of the primate family tree, neither ape-like nor chimp-like, yet not human either. Both were bipedal - they walked upright.
From the collection of nine fossilised teeth from multiple C abyssinicus individuals, the team surmised that these teeth were gorilla-like, adapted for a fibrous diet.
Based on their research from the Chorora, Kadabba and Ardi finds, the team said the common ancestor of chimps and humans lived earlier than had been evidenced by genetic and molecular studies, which placed the split about 5 million years ago.
C abyssinicus also provided fossil evidence that our common ancestor migrated from Africa, not Eurasia, where fossils were more prolific prior to this discovery of multiple skeletons.
Through fieldwork, volcanic ash chemistry and geochronology, researchers nailed down the age of the fossils to approximately 8 million years old.
The study was published in the journal Nature.
