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HOMO NALEDI | Bones unearthed in South Africa

Found with help from UW scientists, newly discovered species is 'cousin' of humanity

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Homo naledi reconstruction
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A few months after a team of excavators pulled more than 1,500 bones from a cave outside Johannesburg, South Africa, dozens of experts in the anatomy of human ancestors were brought to the city in spring 2014 to determine what had been found.

Caroline VanSickle, a UW-Madison postdoctoral fellow and expert on the pelvis of Neanderthals and other hominids, was one of them. She and the team of scientists spent their days poring over the bones and fossil records in a workshop, and their nights swapping theories about the discovery over dinner and beers.

The researchers couldn’t agree on what species they thought the bones belonged to — some believed it was a member of humanity’s genus, Homo, while others said it had to be a more distant relative, Australopithecus. As the work continued, the scientists came to realize why there was no consensus.

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Excavators in cave

In this image from the October 2015 issue of National Geographic, researchers Megan Berger and Rick Hunter move through a narrow section of the Rising Star cave near Johannesburg, South Africa, on their way to a chamber where excavators found more than 1,500 bones from at least 15 Homo naledi individuals.

“This is something totally different,” VanSickle said.

What the scientists found was a species of human ancestor that had never been identified before: Homo naledi, an upright-walking hominid believed to be like a cousin on our family tree.

Homo naledi had humanlike hands, teeth and feet, but its cone-shaped rib cage and wider pelvis were features of earlier ancestors, UW-Madison anthropology professor John Hawks said. It had a small brain but exhibited surprisingly advanced behavior, Hawks said.

He and VanSickle will join several other scientists in South Africa to announce the discovery Thursday, when the first academic papers about Homo naledi will be published.

The announcement is the result of years of work that began with the difficult task of excavating the bones in 2013 — a find made possible with the help of another UW researcher — and continued with the extensive effort to identify the new species.

Homo naledi could shed more light on the ancestors from which humans evolved, said Hawks, who helped oversee the excavation and identification process. Its discovery alone — the hundreds of bones is the largest single hominid fossil discovery ever in Africa, officials say — was an unprecedented find that could spur decades of research.

“There has literally never been a discovery like the one we’ve made,” Hawks said. “There’s nothing like it.”

Finding Homo naledi

Before VanSickle and others could identify Homo naledi, the research team first had to remove its remains from the difficult-to-reach Dinaledi chamber of the Rising Star cave northwest of Johannesburg, for which it is named.

Rising Star cave graphic

A National Geographic illustration shows the difficult journey a team of six excavators, one of whom came from UW-Madison, had to make in November 2013 to reach the Dinaledi chamber, where more than 1,500 Homo naledi bones were found.

Lee Berger, a renowned anthropologist at the University of the Witwatersrand in Johannesburg, which led the project, posted a call for help on Facebook in fall 2013. What he and his colleagues needed, UW graduate student Alia Gurtov said, was a team of “small-bodied, well-trained excavators who could drop everything at a moment’s notice and work collaboratively somewhere very small in South Africa.”

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National Geographic Homo naledi cover

The October issue of National Geographic magazine describes the newly identified Homo naledi species, which shares traits with both Homo sapiens and our earlier ancestors, as “Almost human.”

Gurtov — who describes herself as “barely” 5-foot-2 — met those requirements and went to the site for three weeks that November, squeezing through the cave’s narrow confines for 20 minutes each way until she reached the site where the remains had been discovered a few weeks earlier.

With Hawks and other researchers observing the excavation on TV monitors above ground, National Geographic documenting their work and several people live-tweeting the excavation, Gurtov and five fellow excavators began bringing the bones to the surface.

‘Game-changing’

find

Excavations often turn up scant traces of early hominids, Hawks said. Major discoveries are sometimes the result of finding just a single bone.

But it quickly became clear the Rising Star cave held far more than one bone. By the second day, Gurtov and her fellow excavators had found the remains from four individuals.

The excavation ultimately turned up bones from at least 15 hominids, who ranged in age from newborn to elderly. It was unlike anything the researchers had ever seen, Hawks said.

“A complete game-changer,” Gurtov said.

She and the excavators realized much of the floor of the cave was made up of bones.

“Usually the hominid is the needle in the haystack,” Hawks said. “We had a haystack where everything was a hominid.”

Hawks uses another analogy for the discovery. If you think of the fossils of humanity’s ancestors as a window into our evolution, he said, a normal excavation might yield the equivalent of a pinhole for researchers to look through. This excavation was like opening a garage door.

The fact that excavators found so many bones in such a small, hard-to-reach area led to another surprise: None of the bones had teeth or drag marks, and scientists found only Homo naledi remains in the cave, which means they probably weren’t brought there by a predator. There is no evidence of flooding in the cave, so it’s also unlikely the bodies washed into it.

Instead, researchers believe the Homo naledi intentionally brought and stored their dead in the chamber — behavior considered shockingly advanced for a species with such a small brain.

“It’s a kind of behavior that we don’t see until much more humanlike hominids,” Gurtov said.

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Homo naledi bones

A skeleton of a Homo naledi individual and hundreds of other bone fragments are shown at the University of the Witwatersrand in Johannesburg, South Africa. Each of the pieces was pulled from a remote chamber of a cave near the city.

Work to continue for years

With its mix of humanlike features and other traits associated with earlier species, anthropologists believe Homo sapiens and Homo naledi share common ancestors but likely occupy different branches on the human family tree.

Researchers will publish papers this week in the journals eLife and Nature Communications describing the new species and its features, as well as the cave where it was found. Many more papers will follow describing Homo naledi’s unique anatomy.

There are still many unanswered questions about Homo naledi, among the biggest being when the species walked the earth.

The only estimate researchers have is that the bones they found are between 100,000 and 2 million years old.

Efforts to more narrowly date the species have not yet been successful, but Hawks said he hopes that will change within a couple of years.

Other work on the Homo naledi remains could continue for decades.

Because the researchers found individuals of so many ages, the remains could shed new light on how human development evolved, Hawks said.

“It’s going to take us years to understand that,” he said.

The find could even challenge earlier research, as the more complete Homo naledi remains might potentially show prior theories about the anatomy of our hominid ancestors were incorrect.

“We have a lot of work cut out for us,” Gurtov said.

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Nico Savidge is the higher education reporter for the Wisconsin State Journal.