Ellen Bartlett looks at the significance of the discovery of the bones of two children near Sterkfontein
The question that probably will never be answered is how the bodies of two children ended up in a cave on the farm called Drimolen. Perhaps they died there, of cold, disease, starvation. Perhaps they died nearby, and their bodies were washed in by the rains, or carried in in the mouth of a carnivore – a brown hyena, or sabre-toothed cat.
The first child passed away at about three years of age, perhaps as young as two. At the time of death, he, or she, was probably teething.
The second died in early infancy, at an age no more than about 8 to 10 months.
However they ended up in the cave, they lay there for 1,5 to two million years, slowly becoming entombed in soil and rock, until they were unearthed earlier this year by a research team excavating the site.
The older of the two children is being described as a member of the genus Homo, the line that led to modern humans; the infant is described as Paranthropus robustus (also known as Australopithecus robustus), one of the small-brained, vegetarian ape-people that went extinct about a million years ago.
The two were found not far from one another, in a block of cave sediment at a depth of 4,2m, in remarkably good repair for all their years underground. Andre Keyser, director of the excavation at Drimolen, one of South Africa’s newest and most promising hominid fossil sites, announced the discovery at a press conference earlier this week in Paris.
The fossils are important, Keyser said in an earlier interview at the site, because of their age – both their antiquity, dating from the Plio-Pleistocene era, and the tender years of the children – and because of the fossils’ relative completeness and good state of repair.
They secure Drimolen’s place as one of the richest hominid fossil sites in South Africa – only the long-excavated sites of Sterkfontein and Swartkrans have produced more prehuman and early human fossils.
The remains of the early human child include the lower jaw with two baby teeth and the child’s first permanent molar – which had not yet erupted and was still pushing its way through the child’s gum. Next to the jaw were the bones of the child’s forearm, the radius and ulna. Pieces of the child’s skull, say some of the scientists involved, may be enough to calculate the size of the child’s brain.
The remains of the second child, found a few weeks after the first, consist of both maxillae – the two halves of the child’s upper jaw, two baby milk teeth, and the frontal bone of the child’s skull.
The state of development of the teeth indicate it was a tiny baby, probably the youngest in years of any early hominid found. The two sets of bones have both been estimated at 1,5 to two million years old.
Excavation at Drimolen is partly funded by the French government, and French palaeontologists visiting the site recently said the children may be the youngest members of their respective species yet found in such complete fossil form.
“We’ll get a lot of information that wasn’t available to us before,” said Martin Pickford, a French palaeoanthropologist who has done considerable work in southern Africa, “These babies were still infants in arms, totally dependent upon their mothers for everything.”
Phillip Tobias, retired head of the Palaeoanthropology Research Unit at the University of the Witwatersrand, called the fossils “miraculous discoveries” and complimented Keyser’s skill in “bringing to light two specimens whose teeth are not fully developed, whose skull bone is eggshell thin”.
Wrapped in tissue, the entire fragile assemblage of bits and fragments fits into a margarine container. “The environment is very much against the preservation of delicate things,” Keyser said as he lay them out for viewing. “These just survived.”
“This is the Paranthropus baby,” he said, “You’re looking into its eyes.” More accurately, one could look into where the eyes would have been, under the arched frontal bone. “Though it was probably no more than eight months of age when it died, its development was equivalent to a human baby of 11 to 14 months,” he said. “One wonders what tragedy led to the death of this lovely little baby.”
The remains of the early human are more complete; scientists are particularly excited about finding the bones of the arm – post- cranial bones are rare in hominid fossils.
The breccia containing the fossils was found by the site foreman, Oupa Mosotho; it was being prepared by two French researchers, when one of them noticed what he believed to be a primate tooth. He showed it to Colin Menter, a Wits graduate student involved in the excavation, who recognized it immediately. The other remains followed over the next few weeks.
Keyser found Drimolen after three years searching for a site to excavate, mostly on foot in the dolomite hills west of Johannesburg. He had been invited by a neighbouring farmer to look at sinkholes on his property, and noticed the old limeworks. He hiked over and crawled under the trees and immediately found a primate skull. On his third visit to the site he found his first hominid fossil, a tooth, and since then has found 47 specimens, all Paranthropus robustus. The toddler is the first specimen of early homo.
From the preponderance of the robust pre- humans, and the recent appearance of early homo, Drimolen seems a similar site to nearby Swartkrans, excavated over a 21-year period by Bob Brain of the Transvaal Museum.
“The significance of [Drimolen] is that it is another site telling a very similar story,” Brain said. “A cave is a natural concentrator … The strength of cave deposits is their incredible richness in numbers of individuals. This is a very rich site.”
More than 80% of the hominid fossils found at Swartkrans were classified as sub-adult, including juveniles and infants. They include the skull of an 11-year-old child that had been punctured in two places.
Brain found the punctures had been made by a leopard’s canine teeth; the child’s grisly fate helped him form his theory of early humans as prey, not predators.
Inevitably new fossil finds invite more questions than answers, and Drimolen will probably prove no exception. But the recent finds may also settle a long-standing debate, about whether the traits used to identify adults can also be found in infants. And in so doing, they promise to put to rest the old debate about whether the Taung child, South Africa’s first and most famous fossil, was a robust or gracile australopithecine youngster. It had been speculated that the Taung child was not, in fact, Australopithecine africanus, but a young Paranthropus whose robust characteristics had not yet developed at the age the child died.
But the frontal bone of the Drimolen infant is clearly identifiable as Paranthropus by its thin brow ridges and by the slight depression at the glabella, the point where the eyebrows meet.
“It confirms that it is possible to tell the difference in the infants between Australopithecus africanus and Paranthropus,” said Ron Clarke, a Wits University palaeoanthropologist and director of excavations at Sterkfontein. “You can actually see what makes up the generical species differences. If they’re present in such a young individual, it shows they’re sigificant, not something that just develops in the adult. They’re part of the genetic make-up.”
There is much work to be done on the fossil babies, faunal dating is still in progress. And excavation at Drimolen is equally in its infancy. Researchers are still digging trenches, to try to determine where the cave system begins and ends.
Said Keyser: “We have barely scratched the surface.”