Scientists have long wondered how Lucy, the famous human ancestor, died. Thanks to researchers at the University of Texas at Austin, we may now have an answer.
"Lucy, a 3.18-million-year-old specimen of Australopithecus afarensis - or "southern ape of Afar" - is among the oldest, most complete skeletons of any adult, erect-walking human ancestor," UT said in a news release Monday.
Her partial skeleton was found in 1974; research indicates she was a young adult when she died millions of years ago.
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Now a new analysis of her fossil bones suggests a possible answer as to what led to her premature death -- the upright-walking Lucy probably died after falling from a tree.
"It is ironic that the fossil at the center of a debate about the role of arborealism in human evolution likely died from injuries suffered from a fall out of a tree," said lead author John Kappelman, a UT Austin anthropology and geological sciences professor.
Kappelman took 35,000 CT slices to create a digital archive of Lucy's remains. While studying the slides, he noticed something unusual.
"The end of the right humerus was fractured in a manner not normally seen in fossils, preserving a series of sharp, clean breaks with tiny bone fragments and slivers still in place," the university said in a news release.
"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 Kappelman, who consulted Dr. Stephen Pearce, an orthopedic surgeon at Austin Bone and Joint Clinic, using a modern human-scale, 3-D printed model of Lucy.
According to the study, Pearce confirmed, "The injury was consistent with a four-part proximal humerus fracture, caused by a fall from considerable height when the conscious victim stretched out an arm in an attempt to break the fall."
Similar, but less severe, fractures were also found in the shoulder, ankle, knee, pelvis and ribs. No evidence of any healing was found, indicating the injury may have caused Lucy's death.
Kappelman theorized that Lucy fell from a tree, from a height of more than 40 feet, and that she was likely in the tree foraging or seeking refuge at night.
"Kappelman hypothesized that she landed feet-first before bracing herself with her arms when falling forward, and 'death followed swiftly,'" the university said, quoting Kappelman.
"When the extent of Lucy's multiple injuries first came into focus, her image popped into my mind's eye, and I felt a jump of empathy across time and space," Kappelman said. "Lucy was no longer simply a box of bones but in death became a real individual: a small, broken body lying helpless at the bottom of a tree."
Still, some scientists, including Lucy's discoverer, disagree with UT's finding. They contend the cracks in Lucy's bones came after her death. The disagreement highlights the difficulty of pinpointing a cause of death from fossilized remains.
The new study was published Monday in the journal Nature and was led by researchers at the University of Texas at Austin.