Scientists just solved a 3-million-year-old mystery about one of our early human ancestors

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Lucy, one of the most famous human ancestor fossils, may have fallen from a tree to her death 3.18 million years ago, according to a new study published in the journal Nature. Fractures to her skeleton suggest she plummeted from more than 40 feet and hit the ground at more than 35 miles per hour.

Lucy is a member of the Australopithecus afarensis group of human ancestors. She is one of the oldest and most complete ancient human fossils, so scientists have to take great care when studying her.

Lucy's body: Anthropologist John Kappelman and a team of scientists put Lucy through a machine that creates high-resolution digital scans. The resulting images are higher resolution than a medical CT scan, according to the University of Texas at Austin. They created a digital library of 35,000 scans of Lucy's bones.

Part of Lucy's skeletonSource: John Kappelman, UT-Austin
Part of Lucy's skeleton  John Kappelman, UT-Austin

While studying the scans, Kappelman noticed Lucy's humerus was badly fractured.

"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," Kappelman said in a statement.

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Orthopedic surgeon Stephen Pearce confirmed Lucy's fracture resembled the kind of fracture that comes from falling from a high place. There are also smaller fractures on her left shoulder, knee and pelvis and her right ankle. 

"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," Kappelman said.

Lucy's skeletonSource: Lawrence Todd/UT-Austin
Lucy's skeleton  Lawrence Todd/UT-Austin

Lucy's fall: Since her discovery in 1974, scientists have debated whether or not Lucy was part of a species that spent time in trees. Some scientists think that members of A. afarensis used to forage for food in trees and probably slept in trees. 

This new research seems to support that idea.

"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," Kappelman said.

The team has published some of Lucy's scans online so other scientists and the public can examine her skeleton.