17:26 16 November 2011 by Catherine Brahic and Rowan Hooper
As London's Natural History Museum takes delivery of two replica fossils, palaeontologists hint that they have discovered tools with the fossils, and mummified skin on the bones
It is strangely moving to hold it, knowing that this is an exact replica of a hand of one of our most ancient relatives. The bones looked frail and slight lying on the black felt, but fit snugly on my palm, knuckles lining up to knuckles (see photo). This woman, who died 1.9 million years ago after falling down a watering hole in what is now South Africa, had hands remarkably similar to mine.
This morning, the University of the Witwatersrand in Johannesburg, South Africa, gave a full cast of her fossil to the Natural History Museum in London, along with a cast of a child of the same species, Australopithecus sediba. Together, the two impressive fossils are calling into question the history of our species, and offering never-seen-before insights into how our very early ancestors lived.
At 1.977 million years old, the pair were nearly contemporary with Homo erectus, yet were discovered at the Malapa cave site in South Africa, far from the Great Rift Valley of Ethiopia, which has traditionally been considered the cradle of humanity.
The morphology of their bones – an odd mix of structures similar to ones seen in chimpanzees, australopithecines and even Homo erectus – backs up the notion that this is a transition species. Had some of the bones been found separately, says discoverer Lee Berger of the University of the Witwatersrand, it's likely they would have been ascribed to the different species of Australopithecus.
The fossils' hands and feet suggest that it could climb trees and yet was also bipedal. One possible explanation for these fossils' presence in South Africa, says Chris Stringer of the Natural History Museum, is that environmental changes drove several simultaneous changes in australopithecines across the continent. "It's possible that the environment was becoming drier and more open, encouraging changes like meat-eating and upright walking. What if we were doing this in parallel in different places?"
That could explain the emergence of several transition species at roughly the same time in different parts of Africa, including present-day Ethiopia and South Africa. Most of those species would have died out, leaving just one that evolved into modern humans.
So far we have had only a tiny glimpse at what these two fossils can tell us. This morning, Berger gave tantalising hints of what is yet to come.
Their tooth enamel is being studied for signs of what the pair's diet would have been – and traces of their last meal are still embedded in the crowns of their teeth. Tools have also been found in the area, and are being studied to see if A. sediba could have made them.
If so, they would not be the oldest tools ever found – those date back to around 2.5 million years ago, and evidence of butchery going back to 3.4 million years ago. "But what we have never found is direct association of an early hominid species with lithics [stone tools]," says Berger.
We have to be careful about what we conclude, however, he warns. For one thing, it is hard to definitively associate a tool found at a site with nearby hominid bones. If a fossil were definitely linked to a tool or set of tools, though, anthropologists would have a unique opportunity to explore how our bodies and brains shaped tools, and were shaped by them. "Given the brain, the dental reduction that's taken place, the long arms and the hands, what those tools are and how they're made will give us great insight into the formative process," says Berger.
The two fossils were found in chunks of rock that came out of a deep shaft in the ground. The shaft may have been a watering hole, and one hypothesis is that the woman and boy fell into it while seeking a drink – fractures in the bones may be signs of a fatal fall.
Other bones are sticking out of the sides of that hole, including human bones and the remains of animals that would have been around at the time – antelopes, hyenas and false sabre-toothed cats, for instance. As Berger puts it: "We have the animals and plants that were with them the minute they died."
But the most exciting possibility is that the woman and the boy – nicknamed Karabo – were mummified before they were fossilised. Many of the bones at Malapa are coated in a very thin layer of material that appears to be skin. There is at least the possibility that the two died in a deep, anoxic pool of water, which preserved them in ways never seen before.
If 'the bone coating does turn out to be skin, it will be the first discovery of soft tissue from an ancient hominid. Hair might be present, proteins such as keratin and even DNA might be extracted from the tissue, allowing us to dig even deeper into our history, and determine exactly how this species evolved, or even mated with other hominid species.
"It's not constructive to think about our ancestry as a linear chain of events," says Berger. "As scientists we would not have hoped to believe we could see a transitional, mosaic, evolving species in the mammalian record outside of horses – and here's one in our lineage, which is amazing."