Child's shattered skull may be oldest Homo erectus fossil on Earth

The skull fragment of a 2-million-year-old Homo erectus child found in South Africa

(Image credit: Andy Herries, Jesse Martin and Renaud Joannes-Boyau])

In an ancient cave in South Africa, paleontologists have found evidence that three of humankind's oldest known relatives lived in the same place, at the same time.

That time was roughly 2 million years ago, and the place was the Drimolen Paleocave System near Johannesburg — part of a 180-square-mile (466 square kilometers) network of limestone caverns also known as the Cradle of Humankind.

As their nickname suggests, the primeval caves hold some of the oldest-known fossils of archaic humans. Scientists have unearthed more than 900 hominin fossils at the site, including a near-complete skeleton of a 3 million-year-old Australopithecus africanus — a human ancestor that lived between 3.3 million and 2 million years ago — and the only extant fossils of Paranthropus robustus, an ancestor not directly related to modern humans that lived roughly 2 million to 1.2 million years ago.

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Homo erectus is considered to be a direct ancestor of modern humans (Homo sapiens), thriving for nearly 2 million years before vanishing roughly 110,000 years ago, the researchers wrote. They are the first species on our family tree to have human-like proportions (their name means "upright man") and the first to appear outside of Africa, a 2013 study in the journal Science suggests. Before now, the earliest Homo erectus fossils came from the country of Georgia; the species was hypothesized to have migrated out of Africa around 1.85 million years ago.

Prior studies of Earth’s magnetic field had revealed that one such magnetic reversal occurred 1.95 million years ago. To determine if that reversal was the one that affected the cave's magnetic minerals, the team looked at the ratio of chemical elements in the sediments near the fossil. Because radioactive versions, or isotopes, of uranium atoms decay into lead at a constant rate, the ratio of uranium isotopes to lead in the sample confirmed the minerals were 1.95 million years old. The cranial fossil, they concluded, was even older than this, and dated to approximately 2 million years ago.

Because fossil remains of Australopithecus and Paranthropus found at Drimolen date to the same time period, this research suggests the three archaic hominins all lived side-by-side in southern Africa at the same time — albeit briefly. This era would have been a moment of transition, the researchers wrote, right before Australopithecus went extinct and Homo erectus was just beginning its nearly 2 million-year residency on Earth. Indeed, the authors concluded, it could be that fierce competition with Homo erectus and Paranthropus finally led to the demise of Australopithecus — a possibility never seriously considered until now.

Brandon is the space / physics editor at Live Science. With more than 20 years of editorial experience, his writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. His interests include black holes, asteroids and comets, and the search for extraterrestrial life.