The middle-aged woman and the young boy were out hunting on the African plains when they fell into a sinkhole, dying almost instantly. Shortly thereafter, a monsoon or a flood washed them into a deeper basin, where they were covered with mud and rapidly fossilized.
Nearly 2 million years later, in 2008, anthropologists discovered their nearly complete skeletons in a cave north of Johannesburg, South Africa, a find that experts say is one of the most important of recent times. The hominid pair may be direct ancestors of humans or they may be from a closely related branch on the evolutionary tree, South African researchers report in the journal Science.
"These fossils give us an extraordinarily detailed look into a new chapter of human evolution and provide a window into a critical period when hominids made the committed change from dependency on life in the trees to life on the ground," said Lee R. Berger of South Africa's University of Witwatersrand.
The new skeletons are the only complete specimens that lie between the Australopithecus afarensis known as Lucy, dating from 3 million years ago, and the Homo erectus known as Turkana boy dating from 1.5 million years ago.
In addition to the two hominid skeletons, the team excavated skeletons of at least 25 species of animals, including antelope, mice, saber-toothed cats, a wildcat, a brown hyena, a wild dog and a horse. They also found at least two other hominid skeletons, another woman and an infant, Berger said, but they are not yet reporting on those.
All of the skeletons are in excellent shape because their fall into the pit protected them from scavengers and they were all fossilized rapidly.