Lucy, the most famous fossil of an ancient human cousin, probably died from a fall out of a tall tree that broke multiple bones and damaged internal organs, according to a study led by researchers at the University of Texas.

The researchers, who studied scans of the 3.2 million-year-old skeleton that they took during Lucy’s secret-at-the-time visit to UT for 10 days in 2008, made an unexpected discovery: The upper end of Lucy’s right arm, or humerus, was broken in a way not normally seen in fossils, with sharp, clean fracture edges and tiny bone slivers that would have been dispersed into the soil had the breaks occurred later from normal weathering.

"This compressive fracture results when the hand hits the ground during a fall, impacting the elements of the shoulder against one another to create a unique signature on the humerus," said John Kappelman, a UT professor of anthropology and geological sciences and the lead author of the study, which was published Monday in the journal Nature.

Kappelman consulted with Stephen Pearce, an orthopedic surgeon at the Austin Bone and Joint Clinic and a co-author of the study, who confirmed that the injury was consistent with a fall from a considerable height when the victim, still conscious, reaches out in an attempt to break the fall.

Additional "compressive fractures" in Lucy’s legs, forearms, pelvis and thorax, including the first rib — a hallmark of severe trauma — are also consistent with a fall, illustrating in a brutal, if prehistoric, way the ditty about how "the thigh bone’s connected to the hip bone."

Lucy probably fell from a height of more than 40 feet, hitting the ground in excess of 35 miles per hour, landing feet first before bracing herself with her arms while falling forward, Kappelman said. Death would have come swiftly. A fall from a tree is the most likely explanation because the geology of the area in question shows no evidence of cliffs, he said.

Lucy, a young adult, walked on two legs. But given her small size — 3 feet 6 and 60 pounds — she probably sought nightly refuge from predators by climbing into trees, the study suggests. The question of how much time, if any, Lucy’s species, Australopithecus afarensis, spent in trees has been the subject of vigorous debate since her discovery in 1974 in Ethiopia by anthropologist Donald Johanson of Case Western Reserve University and graduate student Tom Gray.

"I think that Kappelman and his colleagues have made a strong case that Lucy died after falling out of a tree," said Osbjorn Pearson, an associate professor of anthropology at the University of New Mexico, who was not a member of the research team. "There are two primary reasons why chimpanzees and other apes climb trees: to find fruit, which makes up a large part of their diet, and to escape terrestrial predators, especially at night when asleep."

John Fleagle, a professor of anatomical sciences at the State University of New York at Stony Brook, who also was not part of the study, described it as a "fascinating" use of "modern orthopedic literature in conjunction with paleontological and paleoecological research to suggest details of the behavior of an extinct hominin at a level of detail that is rarely available."

The study finds a certain irony in that the physical adaptations that facilitated bipedal locomotion on the ground might have compromised the ability to climb safely and efficiently in trees, predisposing the species to more frequent falls.

Lucy’s official name is A 288-1, but she got her nickname because her discoverers listened to the Beatles song, "Lucy in the Sky With Diamonds," the night she was found.

It was a coup when Kappelman and Richard Ketcham, a professor of geological sciences at UT, hosted Lucy in the basement of the university’s Jackson School of Geosciences in September 2008. The hush-hush stop, after an exhibit of the fossil in Houston, wasn’t disclosed publicly until months later.

As guards and Lucy’s Ethiopian curator stood watch, Kappelman, Ketcham and colleagues at UT gave Lucy the once-over using the university’s High-Resolution X-ray Computed Tomography Facility, which can scan through materials as solid as a rock and at a higher resolution than a medical CT. Lucy, in a way, is a rock, having become highly mineralized as a fossil.

The UT researchers created a digital archive of more than 35,000 CT slices at the thickness of human hair.

"There’s only one Lucy, and you want to study her as much as possible," Ketcham said. "CT is nondestructive. So you can see what is inside, the internal details and arrangement of the internal bones."

The Ethiopian National Museum is providing a set of three-dimensional files of Lucy’s shoulder and knee for public viewing and downloading. The 3-D files and other materials will be available at eLucy.org.

Although Kappelman has been a student of Lucy for decades, he now sees her as more than "just three boxes of bones," as he put it in an interview with the American-Statesman. It’s rare that the cause of death is preserved in a skeleton.

"It brought her to life for me," he said. "In her death, she became a real individual. We’ve all fallen, stretched our arms out. I could identify with her in a way I never did before."