Protohuman Lucy likely died after falling out of a tree, study finds

Lucy, the well-known pre-human who lived approximately 3.2 million years ago, likely died due to injuries sustained after she fell out of a tree, researchers with the University of Texas at Austin and their colleagues reported in a new study published Monday in the journal Nature.

A three-foot-tall female belonging to the species Australopithecus afarensis, Lucy was originally discovered in Ethiopia in the 1970s, and while her remains led to many discoveries about human evolution, the cause of her death had remained a mystery, according to the New York Times.

Now, a team led by UT-Austin paleoanthropologist John Kappelman revealed that the results of CT scans conducted on her bones during a recent tour of the US revealed injuries consistent with a fall, most likely out of a tall tree – injuries that included several cracks in her leg bones, an odd break in her upper right arm, and a skull fracture, the Times and NBC News said.

The cause of death is particularly ironic, the authors explained, since Lucy has been at the center of a debate regarding whether or not her species (our evolutionary predecessors) were actually tree-dwellers. The injuries detected during the postmortem scans, they wrote, provided “unusual evidence for the presence of arborealism in this species.”

Compressive injuries consistent with a fall from about 40 feet

Kappelman and colleague Richard Ketcham, a geological sciences professor at the university, studies Lucy in 2008 during her American museum tour. They scanned the remains at the High-Resolution X-ray Computed Tomography Facility for 10 days, creating an archive of more than 35,000 CT slices of the 40% complete skeleton, the university said in a statement.

During his analysis of those scans, Kappelman discovered that Lucy’s right humerus sustained a break consistent with a compressive fracture – one occurring when the hand hits the ground hard during a fall, impacting elements of the shoulder against each other. In Lucy, said fall produced a series of sharp, clean breaks that still contained well-preserved fragments of bone.

The discovery was confirmed by Dr. Stephen Pearce, an orthopedic surgeon at Austin Bone and Joint Clinic, using a modern human-scale, 3D printed model of Lucy. Dr. Pearce also determined that the fall had to have occurred at a considerable height and that the fracture itself happened as Lucy attempted to stretch out her arm to catch herself while plummeting to the ground.

Furthermore, the researchers found similar but less severe fractures at the left shoulder, as well as a series of other compressive fractures throughout her body, including a pilon fracture of the right ankle, a fractured left knee and pelvis, a fractured first rib. Since they found no evidence of healing, they concluded that the breaks all occurred around the time of death.

Kappelman proposes that Lucy, who would have only been about 3’ 6”  inches tall and weighed about 60 pounds, likely foraged in trees and sought refuge there each night. After comparing her to chimpanzees, he and his colleagues believe that she likely fell from a height of approximately 40 feet, traveling at a speed of over 35 mph, and landed feet-first before she attempted to brace herself with her left arm. Death, Kappelman told NBC News, “followed swiftly.”

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Image credit: Marsha Miller/University of Texas at Austin

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