Latest technology reveals secrets of new hominid

Using the latest imaging technology, researchers are discovering the secrets of two skeletons, nearly 2 million years old, giving them a rare opportunity to view a previously unknown species that scientists say fits the transition from ancient apes to modern humans. The fossils, between 1.95 million and 1.78 million years old, were unearthed in South Africa and have been named Australopithecus sediba, meaning "southern ape, wellspring," to indicate their relation to earlier apelike forms and to their features later found in more modern humans. Researchers classified the species as Australopithecus, rather than Homo, because of their upper body design and brain size. According to the researchers, A. sediba had an advanced hip bone and long legs, allowing it to stride like humans, but also had long arms and powerful hands like an ape. Lee Berger, a paleoanthropologist at the University of the Witwatersrand, says the skeletons provide an extraordinarily detailed look into a new chapter of human evolution when hominids made the committed change from dependency on life in the trees to life on the ground. "They represent a completely new and unexpected species of human ancestor designs, something we did not think was there," he says. Berger brought one of the skulls to European Synchrotron Radiation Facility (ESRF) in Grenoble, France to be examined by X-ray synchrotron microtomography. The resulting images are unique views of a hominid skull still embedded in rock. "This is something never before seen, the inside and the outside of a hominid skull still embedded in rock. That is a scan at 45 microns, one half the width of a human hair. That is not a photograph," says Berger, adding that the technology allows them to see incredible detail. Microns are the millionth part of a metre. Berger explains the technology further: "We have done things like CAT-scan these… creating remarkable images that have allowed us to leave part of the evidence for future generations of science, like the rock attached to it. We can eliminate that rock now with science, by making it invisible, creating remarkable images like those that you see in front of you. We can thus peer inside of places that normally might have been damaged. We can put the pieces back together and you can now look into the face of a skull 1.9 millions years ago, that many parts of it have never been touched by a preparation tool. [That is] something that could not be done before." The technique was developed by ESRF scientist Paul Tafforeau to study fossil primate teeth without damaging the fossil and providing synchrotron imaging for palaeontology. A synchrotron is an accelerator in which charged particles are accelerated around a fixed circular path by an electric field and held to the path by an increasing magnetic field. The synchrotron enables scientists to literally visualize the inside of a fossil block, sometimes up to the micron scale without breaking it open, with contrast, sensitivity and resolution far above those offered by conventional X-ray machines. The X-ray beams from a synchrotron like the ESRF are a thousand billion times more intense than a hospital X-ray machine, and they are, like a laser beam, finely focused. Computed tomography (CT) is an X-ray technique to generate a three-dimensional X-ray image from a large series of two-dimensional X-ray images which are "layered" one next to the other like a series of thin slices. The high intensity and fine focus of the X-rays at the ESRF make possible CT images one hundred times sharper, and with much more contrast, than those of hospital X-ray machines. The resolution of these images is in the micrometer region, and the technique is therefore called micro-tomography. Berger explains the advantages of the technology: "What we have here is the highest resolution scan of an object this size that we can do anywhere in the world. It's a fossil skull of a new species of human ancestor from South Africa dating to about 1.9 million years. And what it's gonna do is to allow us to look at internal morphology, the age of death and structures we can't even imagine, in a way that's quite literally unprecedented in paleontological sciences." Over the two week analysis at Grenoble, in addition to the skull, many fragments of the skeleton, representing nearly forty percent of an entire body, were also studied. The team were particularly interested in the skeleton's teeth which will help them ascertain the precise age of the individual when they died and for clues about the way they lived and what they ate 1.9 million years ago. The technology allows the scientists to add a new level of detail to their research. They were able to examine remnants of soft parts of the body that normally do not fossilise, such as brain tissue, without damaging the skull. The analysis of the data obtained from the X-rays has only just begun, but already interesting details have emerged such as fossilised insect eggs whose larvae could have fed on the flesh of the hominid after death. This is the second hominid skull to have undergone examination by powerful synchrotron radiation. Berger and colleagues describe the find in the current issue of the journal Science, published April 9, 2010. Modern humans, known as Homo sapiens, descended over millions of years from earlier groups, such as Australopithecus, the best-known example of which may be the fossil Lucy, who lived about a million years before the newly discovered Australopithecus sediba. The two new fossils were found in a pit in what was once a cave, their bones preserved by hardened sediment that buried them in a flood shortly after they died, according to researchers. One was a female believed to have been in her late 20s or early 30s. The other was a male likely aged 8 or 9. Two more have been found since the discovery, but Berger declined to detail them. Both the female and the juvenile were 1.27 meters tall (about 4 feet 2 inches). The female would have weighed 33 kilograms (about 73 pounds) and the child 27 kilograms (about 60 pounds). Berger says their features suggest that the transition from earlier groups to the Homo genus occurred in very slow stages. He adds that Australopithecus sediba could help unlock the secrets of the development of the genus Homo, even if it turns out to be a side branch.—AP