Early Human Fossils, Said To Be Australopithecus Sediba, Revealed In Rock By CT Scan

Early Human Bones Part Of 'Paleoanthropological Jackpot'

By Kate Wong

Readers of this blog may have noticed that I’m obsessed with a recently discovered member of the human family tree: the nearly two million-year-old Australopithecus sediba, discovered at a site called Malapa near Johannesburg. There are several reasons for this fixation. For one thing it’s new—it isn’t every day that a previously unknown human relative comes to light, and this one may bear on the mysterious origin of our own genus, Homo. For another, the fossils are extraordinarily well-preserved and include features that have never been seen before in fossils this old, including tartar and probable skin. And third, it is abundantly clear that much more material remains to be recovered from Malapa, which I visited last fall. It’s a paleoanthropological jackpot.

Now comes news that CT scanning of a block of rock recovered three years ago from the site has revealed additional bones that are believed to belong to one of the two A. sediba skeletons that were unveiled in 2010. That would “almost certainly” make the skeleton of the young male A. sediba, nicknamed Karabo, “the most complete early human ancestor skeleton ever discovered,” said Malapa project leader Lee Berger of the University of the Witwatersrand in a statement. On May 19 Berger and his wife Jackie Smilg, a radiologist who is now working toward a Ph.D. on the CT scanning of fossils entombed in rock, spotted the bones concealed in the rock. “We have discovered parts of a jaw and critical aspects of the body including what appear to be a complete femur (thighbone), ribs, vertebrae and other important limb elements, some never before seen in such completeness in the human fossil record,” Berger said.

CT-scanning of this large rock from the site of Malapa in Johannesburg revealed bones that may belong to the Karabo skeleton. Image: Courtesy of Lee Berger

A complete thighbone would be an especially big deal. The Karabo skeleton already has the better part of a shinbone, and the addition of a thighbone would help researchers to observe the length of the leg, which is important for reconstructing locomotion and comparing limb length in A. sediba to that of other fossil human species. (Already the foot and ankle of A. sediba indicate that it had a peculiar way of walking.)

More fossils will probably show up in CT scans of other blocks of rock from the site, many of which were blasted out of the ground by limestone miners in the early 1900s. When I visited Berger last year, a dedicated room at the university held floor-to-ceiling shelves of rocks recovered from the site. While I was there, excitement erupted when one of the team members showed up at a staff gathering holding a replica of a first rib bone from A. sediba that had been imaged with a micro-CT scanner and then “printed” using a 3D prototyper, thus allowing the researchers to observe and study the bone without ever removing it from the rock it was embedded in. Berger and his colleagues have speculated that the skull belonging to the adult female skeleton will eventually turn up in one of these blocks, and that they might take the same approach to studying it that they have taken with the rib bone, relying on imaging and 3D printing rather than freeing the skull from the surrounding rock, which is extremely laborious.

CT scan of rock shows two molars (circled in white) in a mandible of A. sediba. Image: Courtesy of Lee Berger

In the case of the newly spied bones of Karabo, however, the team plans to excavate them from the rocky matrix—and in full view of the public. During a visit to the Shanghai Science and Technology Museum on July 12, Berger announced plans to develop a specially designed lab studio in the Maropeng Visitors Center in the Cradle of Humankind that will allow people to observe the preparation of the fossils in real time, either in person or via the internet. “With the assistance of a number of partners, we are going to build into this lab studio a viewing platform for every person on the planet to watch us recover these important fossils. With cameras, interactive displays and audio channels, the world will be able to watch this exciting find emerge over the next several years,” he said in his speech.

CT scan of the rock also revealed a fibula (circled in green) and a probable femur shaft (the two dark parallel lines above and to the left of the fibula). Image: Courtesy of Lee Berger

Live preparation of early human fossils would be unprecedented, as far as I know. Paleoanthropologists tend to keep their finds under wraps until they publish their descriptions of the finds. And even then, other researchers (never mind the public) may have difficulty getting access to the remains. Berger has been praised for his efforts to make the A. sediba material widely available to scholars, even ahead of publication. It will be interesting to see if other paleoanthropologists follow his lead in letting the public in on the adventure as it happens.

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