Fossil teeth from Africa add years to early ape.
The last common ancestor of humans and gorillas might have lived at least 2 million years earlier than previously thought. Fossilized teeth of the earliest gorilla ever discovered, dating to 10 million years ago, have been found in Africa, say researchers.
The new species (Chororapithecus abyssinicus) from Ethiopia, reported on page 921 of this issue, helps to fill in a huge gap in the fossil record. The team of Ethiopian and Japanese researchers has based its conclusion on just nine teeth from at least three individuals of the species, which were discovered in the desert scrubland of Afar about 170 kilometres east of Addis Ababa.
The teeth, eight molars and a canine, “are collectively indistinguishable from modern gorilla subspecies” in size, proportion and scan-revealed internal structure, says Gen Suwa of the University of Tokyo Museum, Japan, who led the study. The team argues that the gorilla's divergence date from the human lineage is not about 8 million years ago as previously surmised (S. Kumar et al. Proc. Natl Acad. Sci. USA 102, 18842–18847; 2005), but “greater than 10 to 11 million years ago” on the basis of the age of the new species. Functionally, he adds, the teeth already seem to be evolving — they could shear through a plant diet, a gorilla trait — although other herbivore apes also exist in the fossil record.
Africa was the place of origin of both humans and modern African apes.
This finding could prompt discussions of how anthropologists and geneticists determine the hominin line's divergence from chimps, previously pegged at about 6 million years ago. “Chororapithecus abyssinicus suggests, once again, that Africa was the place of origin of both humans and modern African apes” — not Eurasia as some researchers have argued, says Suwa.
But palaeoanthropologist Jay Kelley, who studies primate teeth at the University of Illinois at Chicago and was not involved in the study, is sceptical. “I'm not convinced it is a gorilla,” he says. More fossils, analysis and debate will be needed to determine whether the specimen is ancestral to hominids, he adds. For now, he would be “very cautious” about using the specimen to realign divergence dates between hominins and gorillas–chimps.
Suwa's team is part of the Revealing Human Origins Initiative (RHOI), a project that searches at multiple sites in Africa, Europe and Asia for species that predate the earliest known hominid, the 7-million-year-old Sahelanthropus tchadensis (M. Brunet et al. Nature 418, 145–151; 2002).
Between 15 million and 22 million years ago, there were dozens of primate species across Africa and Euroasia — and apes dominated the primate scene. But fossils show that these species don't share the characteristics of modern African apes. “From that species pool, the common ancestor of African apes and humans branched out,” says Tim White, a palaeoanthropologist at the University of California, Berkeley, and an RHOI director. “And the goal of RHOI is to find the common ancestors. With C. abyssinicus, we now can see an ancestral African ape.”
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Dalton, R. Oldest gorilla ages our joint ancestor. Nature 448, 844 (2007). https://doi.org/10.1038/448844a