HOUSTON  - AUGUST 28:  A sculptor's rendering of the hominid Australopithecus afarensis is displayed as part of an exhibition that includes the 3.2 million year old fossilized remains of "Lucy", the most complete example of the species, at the Houston Museum of Natural Science, August 28, 2007 in Houston, Texas. The exhibition is the first for the fossil outside of Ethiopia and has generated criticism among the museum community and others that believe the fossil is too fragile to be moved from it's home country. (Photo by Dave Einsel/Getty Images)
Dave Einsel/Getty Images North America/Getty Images
HOUSTON - AUGUST 28: A sculptor's rendering of the hominid Australopithecus afarensis is displayed as part of an exhibition that includes the 3.2 million year old fossilized remains of "Lucy", the most complete example of the species, at the Houston Museum of Natural Science, August 28, 2007 in Houston, Texas. The exhibition is the first for the fossil outside of Ethiopia and has generated criticism among the museum community and others that believe the fossil is too fragile to be moved from it's home country. (Photo by Dave Einsel/Getty Images)
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Story highlights

Lucy, the Australopithecus fossil, is iconic. But how did she die?

In a new study, researchers hypothesize that she fell from a high tree

(CNN) —  

When Lucy, the world’s most well-known fossil, was discovered sticking out of a shallow Ethiopian stream bed in 1974, she provided new insight about life for early human ancestors 3.18 million years ago. The image of her skeleton – which is estimated to be 40% complete and considered the best representation of her species, Australopithecus afarensis – became iconic.

But how did she come to rest in that shallow stream? Lucy just might be considered one of the world’s oldest cold cases.

Forty-two years after the discovery, researchers from the University of Texas at Austin now believe that she was found in proximity to where she died, and that she fell from a great height to her death.

“When we think about any of the fossils that we work on, we know in every instance that that came from an individual who was born, they grew up, and then they died,” said John W. Kappelman, a professor of anthropology and lead author of a new study on Lucy. “But it’s rarely the case that the skeleton actually preserves evidence of how an individual died. What we’re proposing here is the first hypothesis that’s out there, and we’ve had her for 42 years now, about how she died. I am not aware that anyone else has ever [done that].”

The original fossil and CT scans of fractures to her skeleton paint a more vivid portrait of what happened in Lucy’s final moments, and although it was probably swift, it wasn’t without pain. The new study that proposes the hypothesis reads like a coroner’s report, making Lucy’s stone-like bones seem more lifelike than ever.

ENNY VAUGHAN/AFP/Getty Images

What happened to Lucy?

Lucy was small, about 3½ feet tall and 60 pounds. Analysis of her skeleton and teeth shows she had reached maturity, but not unlike chimpanzees, her species matured young. Kappelman estimates she was 15 or 16 years old.

Given her size, predators such as hyenas, jackals and saber-toothed cats would have posed a threat to Lucy. So Lucy most likely turned to the trees, Kappelman said. It’s possible she scaled them only from time to time for safety or that she nested in them every night. Based on data on the nesting habits of chimps, an average of 46 feet above the ground makes them feel safe.

She stood up straight, with feet, knees and hips that are similar to ours. If you saw her walking from afar, you would think Lucy was human by her silhouette. But up close, she had a small head, a brain comparable in size to a chimpanzee’s, longer arms and hair covering her body.

Bridging the gap between humans and chimps, Lucy had slightly curved fingers and toes, with mobile ankles and shoulders that provided more overhead range of movement. Even with those abilities, she would have been better at walking than climbing.

Perhaps Lucy was spooked by a predator, or perhaps she was asleep or settling in for the night. Maybe she spied some fruit and wanted to forage. Either way, this is what Kappelman believes happened next.

A sculptor's rendering of the hominid Australopithecus afarensis.
Dave Einsel/Getty Images
A sculptor's rendering of the hominid Australopithecus afarensis.

From 46 feet in the air, Lucy fell out of her tree, fully conscious. She fell toward the ground rapidly at 35 mph and hit feet-first, sending an impact punching through her body that created fractures in her ankles, knees, hip and shoulder. Internal organs were probably punctured by this “hydraulic ram effect.” Lucy pitched forward and instinctively put out her arms to break the fall, creating fractures in the bone there as well. It would probably be her final conscious act.

She twisted to her right, landing primarily on that side. That twist fractured her neck and tilted her head. Unconscious, broken and bleeding, she lay on the stream bed. If there was water present at the time, it gently moved the body a short distance along, naturally carrying her to a final resting place since members of her own species didn’t.

A diagram of Lucy's fall from a tree, showing the overlay of her skeleton.
Courtesy John Kappelman
A diagram of Lucy's fall from a tree, showing the overlay of her skeleton.