Skeleton could be human relative

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 about 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 is now publishing detailed descriptions of the creatures’ heads, hands, feet, and hips. The team date the fossils to 1.98 million years ago, the middle of an era known for a lack of evidence of possible human relatives.

The mash-up of human-like and ape-like traits are like a “a stop-action snapshot of evolution in action,’’ said the director of the Smithsonian Institution’s Human Origins Program, Richard Potts.

The researchers stop short of calling the creatures an ancestor to the human lineage known as Homo. But they place A. sediba in the running for that 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, found Karabo in an area called Cradle of Humankind.

None of the previous finds were preserved in this way. 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.

The foot and ankle are “mostly human,’’ said Bernhard Zipfel, of University of Witswatersrand. Yet, the heel looks more apelike - one of many such anomalies.