Gorilla in the mist of time

An Ethiopian-Japanese research team has discovered fossils from a 10 million-year-old great ape that it believes show that humans and apes split much earlier than suspected.

The fossils - nine large teeth, eight of them molars - were discovered at the south-eastern end of the Afar rift in Ethiopia, about 170 km east of Addis Ababa.

The site is about 190 km south of the famous Middle Awash sites that yielded the early human ancestor fossils Ardipithecus ramidus (4.4 million-year-old) and Ardipithecus kadabba (5.7 million-year-old). Another 70 km north is the famous Lucy (3.2 million-year-old Australopithecus afarensis) site.

The researchers believe the fossils belong to a basal branch of the gorilla line and have named the new ape Chororapithecus abyssinicus.

They claim the find would be the earliest recognised primate that was directly related to the living African great apes (gorillas, chimpanzees and bonobos).

"These fossils show that humans and African great apes probably split much earlier than considered by molecular studies," the researchers said.

The research team was led by paleoanthropologists Dr Gen Suwa from the University of Tokyo, Dr Berhane Asfaw from the Rift Valley Research Service in Addis Ababa, and Dr Yonas Beyene, from Ethiopia's Department of Archaeology and Paleontology. The team published its findings in this week's issue of Nature.

Chororapithecus abyssinicus is named after the exposed patches of sediment that comprise the Miocene Chorora Formation, where the fossils were found.

The researchers believe the teeth show that it shared with modern gorillas some unique specialisation for eating fibrous food stuff such as stems and leaves.

"It's a subtle distinction, but we've compared it with everything we could think of," Suwa said. "And it does show some telling signs of gorilla-like molar structure. If it's not a gorilla relative, then it's something very similar to what an early gorilla must have looked like."

They say Chororapithecus was either a primitive form of gorilla, or an independent branch showing a similar adaptation at about the time when the gorilla line was emerging somewhere else.

"The human fossil record goes back to six to seven million years, but we know nothing about how the human line actually emerged from apes," the researchers say. "Chororapithecus gives us the first glimpse of the ape side background to the human origins story."

They also believe that the find discounts the theory that the direct line of ancestral ape from which gorillas, chimpanzees, and humans emerged was not African, but rather came back to Africa from Eurasia.

"Chororapithecus suggests, once again, that Africa was the place of origin of both humans and modern African apes," they say.

"Chororapithecus indicates that the human-gorilla split was probably greater than 10 to 11 million years ago, which strongly suggests that the widely accepted conventional wisdom based on molecular and DNA studies of a younger human-ape split (younger than eight million years ago) is in fact incorrect."

"Most molecular and DNA studies have concluded that human and gorillas had split by at least eight million years ago, and human and chimpanzees by five to six million years ago.

"However, these conclusions were mostly based on a human-orang split of 13 to 14 million years ago. "Chororapithecus indicates that a reconsideration of this assumption is needed.

"In fact, if the orang line was present in Africa prior first migration of Miocene apes from Africa to Eurasia, then the human-orang split could easily have been as old as 20 million years."

Source: The Ethio-Japanese research team