Doyle Rice

USA TODAY

Talk about cracking a cold case: Nearly 3.2 million years ago, Lucy died. Now we may know how.

Lucy, the iconic human cousin whose skeleton was discovered in Ethiopia in 1974, died shortly after she fell out of a tree, according to a new study published Monday in the peer-reviewed British journal Nature.

More than four decades after her discovery, Lucy remains one of oldest, best and most complete skeletons of any adult, erect-walking hominid, according to John Kappelman, an anthropologist at the University of Texas and the lead author of the study. A hominid is a member of the evolutionary family that includes great apes – such as gorillas, chimps, and orangutans, humans, and their ancestors, some of which are extinct.

Lucy, an example of the oldest known hominid australopithecus afarensis, died at roughly 15 years old in present-day Ethiopia. A small creature, about 3 feet 6 inches tall and only 60 pounds, she probably spent nights in a tree to avoid bigger, potentially dangerous predators, Kappelman said.

Scientists dubbed her Lucy from the Beatles song "Lucy in the Sky with Diamonds," which was played at the archaeological camp the night of her discovery, according to Arizona State University (ASU) Institute of Human Origins.

Using a high-resolution, high energy CT scan of her fossils taken while Lucy was on loan temporarily from Ethiopia to the U.S. for a traveling exhibition in 2007 and 2008, scientists discovered that her upper arm and shoulders were broken. They determined that she probably fell from a height of more than 40 feet, hitting the ground at over 35 mph.

"We were surprised by this," Kappelman said, adding that "rarely is the cause of death preserved in bones."

Based on the pattern of breaks, scientists believe that she landed feet first before bracing herself with her arms as she fell forward, and “death followed swiftly,” the study concluded.

In addition to the broken bones, extensive and catastrophic injuries to her internal organs likely factored into her death.

The way that both of her shoulders were fractured means she likely stretched out her arms to break her fall, which indicates she was conscious at the time of her death.

Other experts who are familiar with Lucy aren't so sure of the findings. "I think the methodology falls short of providing a realistic explanation for the majority of breaks in Lucy's bones," said paleoanthropologist William Kimbel of ASU's Institute of Human Origins. "We see this kind of damage frequently in a wide variety of animals that did not fall from trees," he said.

Bones can be damaged by being trampled, or covered by sediments, or subject to geological pressures, he said. "The authors did not go through the detailed, formal evaulation of alternative explanations of the breaks," Kimbel said.

Otherwise, Kappelman said the discovery supports the theory that our ancestors lived partly in trees, which has long been debated by scientists who study human evolution. Kappelman said it's likely that the species lived partly in trees, known as "arborealism," and partly on the ground.

"It is therefore ironic that her death can be attributed to injuries resulting from a fall, probably out of a tall tree, thus offering unusual evidence for the presence of arborealism in this species," the study said.

According to the study, the adaptations that allowed the species to get around on the ground may have compromised its ability to climb trees safely and efficiently, perhaps making them more likely to fall.

"By understanding her death is how she came alive to me," 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.”