Ever wonder how Lucy, our famed and fossilized human ancestor, died? It turns out she mostly likely fell out of a tree.
A new study at the University of Texas at Austin shows that Lucy's right humerus (arm bone between shoulder and elbow) was fractured in an unusual manner, not typical of most fossils. Lead author John Kappelman, professor of anthropology and geological sciences at UT Austin, noticed that the breaks in the fossil were neat and sharp, with tiny bone fragments still in place.
Lucy is the name for several hundred pieces of bone that comprise 40 percent of the skeleton of a 3.18-million-year-old female Australopithecus afarensis, originally discovered in Ethiopia by paleoanthropologist Donald Johanson and graduate student Tom Gray. While as a "terrestrial biped," Lucy was able to stand erect and walk on two feet, it has also been heavily debated whether Lucy and the rest of her species spent time in trees.
"It's ironic that the fossil at the center of the debate about the role of arborealism [relating to a tree] in human evolution likely died from injuries suffered from a fall out of a tree," Kappelman said in a statement.
Lucy's body was scanned for details at the High-Resolution X-ray Computed Tomography Facility at the university. The CT device used to scan her body can scan through solid materials like rock. "We didn't scan Lucy looking to find out cause of death. We wanted to find out how she lived, not how she died," Richard Ketcham, a geological scientist and head of the facility, told me. "But even Lucy's death sheds some light on her life, and specifically verifies that she spent time in trees."
The scans revealed that the fracture in Lucy's bone resulted from her hand hitting the ground after a fall, impacting her shoulder, and creating a unique mark on her humerus. Dr. Stephen Pearce, orthopedic surgeon at Austin Bone and Joint Clinic used a 3D printed model of Lucy to confirm that the injury appeared to be a "four-part proximal" fracture in the humerus, resulting from Lucy having fallen a distance and extending her arm to break the fall.
Kappelman also observed other, less severe fractures in other parts of Lucy's skeleton, all supporting the theory that she fell, and since these fractures also shown to have not healed, it's likely that Lucy died somewhat immediately after the fall, and possibly at a speed of 35 miles per hour from about 40 feet high.
"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."