Scientists Amazed by Fossils of New Human Ancestor
September 16, 2015
Last week, scientists from the University of the Witwatersrand in South Africa reported on a new find. Lee Berger, an American paleoanthropologist (expert on human evolution), and his colleagues unveiled a huge collection of fossils from the Rising Star cave site, about 30 miles (50 kilometers) northwest of Johannesburg. The fossils represent a previously unknown prehistoric human species. The scientists have named this new species Homo naledi. The Latin word Homo means human being, while naledi means star in the Sotho language of South Africa.
The Rising Star fossil site was first discovered in 2013 when spelunkers (people who explore and map caves) noticed an unusual number of fossilized bones in a huge cave complex they were exploring. The spelunkers alerted Berger, who hired a number of them to help recover the fossils from the narrow tunnels of the large underground caverns. Berger hired spelunkers of small stature to recover the fossils because the scientists could not fit through the narrow passage into the cave—only 7.1 inches (18 centimeters) wide. Over the following months, the team collected 1,550 fossils, representing partial remains of at least 15 individuals—the single largest collection of hominins ever found at a site in Africa. (In scientific classification, hominins are the group that includes human beings and early humanlike ancestors.)
Berger and his colleagues classified the fossils as a new hominin species based on the unusual anatomy of the fossils, which show an odd mix of primitive and modern features. The skull of Homo naledi is rounded like a human skull, yet small, with a brain only about one-third the size of a modern human brain. The front teeth are small, like humans, but the molars (back chewing teeth) are quite large. They had a small, thin body, and the bones of the shoulder and hands suggest they were adept at climbing trees. Yet the legs and feet show they were able to walk upright and possibly to make and use stone tools, as could the earliest humans.
The scientists have not been able to determine the precise age of the fossils, so it is difficult to determine exactly where Homo naledi fits on the human family tree. Most paleoanthropologists think that the first people evolved from an Australopithecus ancestor. Homo naledi may be a very close relative to such an ancestor. The scientists are also puzzled by the Rising Star site itself, which preserves almost no fossils of other kinds of animals. This may indicate the hominins at the site became trapped in an unusual event, such as a flood, and died together. However, Berger suggests that Homo naledi may have intentionally buried their dead at the site, a uniquely human behavior. Such behavior is virtually unknown among other species of early human ancestors.
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