The fossils of a female adult and a juvenile male – perhaps mother and son – are just under two million years old. They were uncovered in cave deposits at Malapa not far from Johannesburg.

Researchers tell the journal Science that the creatures fill an important gap between older hominids and the group of more modern species known as Homo, which includes our own kind. The team has assigned the name Australopithecus sediba to their finds.

“It’s at the point where we transition from an ape that walks on two legs to, effectively, us,” lead scientist Professor Lee Berger of the University of the Witwatersrand told BBC News.

“I think that probably everyone is aware that this period of time – that period between 1.8 and just over two million years [ago] – is one of the most poorly represented in the entire early hominid fossil record. You’re talking about a very small, very fragmentary record,” he explained.
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Their bones were laid down with the remains of other dead animals, including a sabre-toothed cat, antelope, mice and rabbits. The fact that none of the bodies appear to have been scavenged indicates that all died suddenly and were entombed rapidly.

“We think that there must have been some sort of calamity taking place at the time that caused all of these fossils to come down together into the cave where they got trapped and ultimately buried,” said team-member Professor Paul Dirks from James Cook University in Queensland, Australia.

All were preserved in the hard calcified clastic sediment that formed at the bottom of a pool of water.