As one of the best-known species of early humans, Lucy died some 3.18 million years ago. According to researchers, it may be because she fell from a tree.

Lucy is one of more than 300 individuals belonging to the Australopithecus afarensis species, which thrived in East Africa 3.85 to 2.95 million years ago. Specifically, they were found in Hadar, Ethiopia in 1974.

Scientists have been probing fossils from the site since then, but it's only now that researchers like John Kappelman have been able to shed light on what ended Lucy's life.

In 2008, her remains were making rounds as part of a U.S. museum tour. When she stopped at the High-Resolution X-ray Computed Tomography Facility at the University of Texas, her fossils were scanned and high-resolution images of her internal bones were created.

Kappelman and his colleagues spent 10 days scanning Lucy's remains carefully. At the end, they had 35,000 separate scans to examine, some of which showed a series of sharp, clean breaks.

It was these breaks that caught the researchers' attention.

According to Stephen Pearce, an orthopedic surgeon, the breaks were indicative of trauma one would normally get after falling from a considerable height. He also consulted with other orthopedic surgeons and was told the same thing: it's a four-part proximal humerus fracture.

What does this mean?

For starters, Lucy possibly fell from a height of more than 40 feet. This would put her speed at more than 35 mph when she hit the ground. And given the way her upper arm and shoulder bones were fractured and compressed into one another, she had tried to break her fall by stretching out her arms.

Further analysis showed that there were other compressive fractures in Lucy's bones, supporting the researchers' theory that the early human ancestor had fallen to her death. For instance, her right ankle, pelvis and left shoulder and knee were all broken, as well as her first rib. Broken first ribs are rarely observed in emergency rooms today, but they point to severe chest trauma, much like what anyone would get from falling from a height.

"Impacts that are so severe as to cause concomitant fractures usually also damage internal organs; together, these injuries are hypothesized to have caused her death," said the researchers.

Aside from consulting with Pearce, the researchers also examined literature to see if there are other means by which the breaks in Lucy's bones could have been sustained. They were unable to find other possible causes that could explain Lucy's broken bones.

Couldn't have the bones sustained damage before being fossilized? According to the researchers, no. If the damage was sustained after death or when the bones were already dry, then tiny slivers and fragments of bone should have been dispersed from the fracture sites. Additionally, they also weren't older injuries because they don't have signs of remodeling, meaning the breaks were in the bone were sustained at the time of death.

Au. afarensis have feet adapted for walking upright, instead of climbing trees, which may have played a hand in Lucy's demise, said the researchers. Her bones point to curved fingers and strong arms, however, which could have aided climbing. Rather than a simple case of one feature causing the failure of another, it might mean more that Lucy was actually capable of both walking and climbing well. Her falling off a tree was more of an accident.

Kappelman, Pearce and colleagues have published the results of their work in the journal Nature.