THEY don't come much longer in the tooth. This 1.8-million-year-old specimen is the earliest intact skull of a human ancestor ever found, combining a small braincase with a long face and large teeth. The find confirms that the species it belonged to, Homo erectus, was far more variable in appearance than we thought – so much so that its discoverers argue that the human family tree should be pruned of many of its species.
The component parts of the skull were unearthed at the Dmanisi archaeological site in southern Georgia by a team led by David Lordkipanidze of the Georgian National Museum in Tbilisi. The lower jaw was found in 2000, and the cranium turned up in 2005. Since then, the team has managed to reconstruct and date the skull.
"It's a fantastic specimen, unprecedented in preservation for that time period," says Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved in the discovery.
Four other H. erectus skulls have been found at Dmanisi, but this is the best-preserved. The site has also yielded simple stone tools and many animal remains. The researchers say the hominin haul supports the idea that the many species of Homo thought to have coexisted during this period are, in fact, a single species – H. erectus.
To back up this claim, they measured facial differences between the five Dmanisi hominins. These reveal the extent of variation among H. erectus populations, because the five lived in the same place at roughly the same time. The team then compared the Dmanisi finds with a range of fossils belonging to African hominins alive at the same time, and used modern humans and chimpanzees as a reference for the amount of variation expected within a species (Science, doi.org/pcz).
Although the hominin fossils were highly variable, the analysis found that the range of facial differences was not greater than in humans and chimps, suggesting the fossils belong to a single group. The team says they are all one species, meaning hominins like H. habilis and H. rudolfensis are, in fact, H. erectus.
"We are not against the idea that there might have been multiple species 2 million years ago," says team member Christoph Zollikofer of the Anthropological Institute and Museum in Zurich, Switzerland. "But we don't have sufficient fossil evidence to make the distinctions between species."
Other anthropologists are unconvinced. Spoor agrees that the Dmanisi specimens are all H. erectus and that the species was variable, but he does not believe that all the African fossils belong to H. erectus. He points out that the team's analysis suggests that even the much more apelike Australopithecus is part of the H. erectus group. It is not surprising, then, that their analysis misses the more subtle shape differences within the Homo genus, he says.
This article appeared in print under the headline "Can one skull rejig our family tree?"
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