Did fall from tree kill famous human ancestor Lucy?

Because the area in which Lucy’s skeleton was found was low-lying, with no cliffs nearby, they believe she must have fallen from a tree. Lucy’s skeleton is usually kept in Ethiopia, but during a 2008 United States museum tour, researchers at the University of Texas were able to borrow her for 10 days.

They were thrilled to study one of the most complete hominin fossils ever found and scanned her non-stop with the High-Resolution X-ray Computed Tomography Facility (UTCT) that belongs to the UT Jackson School of Geosciences. There, Kappelman used a machine created to scan through materials as solid as a rock and at a higher resolution than medical CT.

In addition, Lucy’s broken right shoulder has some distinctive compression fractures, which might have been a result of her landing on her arms after falling from a great height.

Given that there were no skyscrapers to fall off, and Lucy’s skeleton was unearthed far from any steep cliffs, Kappelman and his colleagues hypothesized that Lucy had been in a tree just before plummeting to her death. He said that fractures postmortem occurs across the bone, but this skeleton’s bones had one side broken while the other remained intact. It’s what orthopedists call a hinge, or greenstick fracture, where the bone bends and cracks.

Her injuries suggest “she stretched out her arms at the moment of impact in an attempt to break her fall”, said Kappelman, who co-authored the study.

“I knew these fractures were there, I just never thought to ask what had caused them”. To check his work, Kappelman consulted with nine orthopedic surgeons who agreed with his analysis. But the debate is certainly moving forward, as the 3D scans have also been released for free as 3D printable files – allowing everyone to study the models for themselves. Similar fractures were observed at the left shoulder and other parts of Lucy’s skeleton, as well as modern examples.

Johanson said it was more likely that Lucy’s fractures occurred long after she died, telling The New York Times that “elephant bones and hippo ribs appear to have the same kind of breakage”. His team zeroed in on a four-part fracture in her right humerus, the bone that runs between the shoulder and the elbow.

If Kappelman’s calculations are correct, Lucy climbed up a 14 meter tree (equivalent to the height of a five story building).

Given her size, predators such as hyenas, jackals and saber-toothed cats would have posed a threat to Lucy. Yet she also had features of a tree-climber. A fall from that height would definitely kill someone. “They go over what they’re trying to do very, very carefully and so it seems to make sense to me”. “There are only a few causes of death that are actually preserved in a bone, so in the most part, when we look at a fossil, there’s no evidence for how it died”. Donald Johanson says the fractures on her bones are “undoubtedly the result of geological forces acting on the bones after they are buried during the process of fossilization”.

Johanson noted that the type of breakage involved in the research is similar to others found on almost 100 percent of other fossils found at Hadar, Ethiopia, including bones from elephants, rhinos, and monkeys.

Scientists have long debated whether Lucy, a small bipedal creature who belonged to an extinct species known as Australopithecus afarensis, spent time in trees (arborealism) as well as on the ground ― a point referenced by the paper’s lead author in a written statement. “But from the waist up, Lucy has an upper body that looks like that of any tree-climbing ape”, said Dartmouth anthropologist Nathaniel J. Dominy for the Washington Post, who wasn’t involved in the study. There are simply too many fractures to be the result of even a great fall, says biological anthropologist Owen Lovejoy at Kent State University in OH, who did a postdoc in orthopedic biomechanics.

Of course, researchers can’t know exactly what was happened to Lucy.