He was built to climb, and yet he strode upright.
His arms hung low like an orangutan's. Yet with his long thumbs and curved fingers he could grasp sticks and rocks like a man.
His brain was not much larger than a chimpanzee's. Yet his widened pelvis implied his kind gave birth to children with much bigger brains.
And so a fossilized adolescent named Karabo — which means "answer" in a South African dialect — is raising a lot of questions about human evolution.
Researchers found his skeleton, and much of an adult female in a cave some 25 miles north of Johannesburg in 2008 and announced the discovery in 2010. They coined a new species, Australopithecus sediba, and launched an intensive multinational effort to study the find.
In the journal Science, the team has published descriptions of the creatures' heads, hands, feet and hips. The team also dated the fossils to 1.98 million years ago, in the middle of an era notorious for its lack of evidence of possible human relatives.
The mash-up of humanlike and apelike traits are like a "stop-action snapshot of evolution in action," said Richard Potts, the director of the Smithsonian Institution's Human Origins Program, who was not involved in the research.
The researchers stop just short of calling the creatures an ancestor to the human lineage known as Homo. But they place A. sediba squarely in the running for that coveted title.
The species is "possibly the best candidate" yet for a Homo ancestor, said Lee Berger of the University of Witswatersrand in Johannesburg. Berger, along with his then-9-year-old son Matthew, discovered Karabo in a fossil-rich region known as the Cradle of Humankind.
None of the previous finds were preserved like this. The duo apparently fell into a deep cave together, where limestone encased the bodies and preserved exquisite detail.
Based on his size, Karabo was just entering adolescence. His companion was an adult female. It's tempting to think of them as mother and son. Berger said they are "likely related," although he presented no evidence other than their proximity in death.