Lucy the Australopithecus, one of the oldest and the most complete hominid fossil ever found, may have been killed by a fall from a tree, scientists have indicated. Their work supports the case that Lucy's species, Australopithecus afarensis, was arboreal (lived in trees) as well as terrestrial (land-dwelling).

Lucy's remains were found in 1974 in Ethiopia and are thought to be 3.2 million years old. A staggering 40% of her skeleton was found, making her a crucial specimen to understand how hominids evolved and how early human species lived. Now, in a study analysing Lucy's remains published in the journal Nature, scientists have also found out more about how she died.

By computing tomographic scans of the skeleton and comparing what they found with modern-day clinical cases, researchers were able to formulate a new hypothesis about the cause of the creature's death – a mystery that had never really been resolved.

Unusual fractures

Like most fossils that paleoanthropologists find, Lucy's bones display a number of breaks, often attributed to the passing of time. However, the analysis led by John Kappelman, from the University of Texas at Austin, suggests that most fractures in this case are likely to have been sustained at the time of death rather than afterwards, and are probably the result of a fall from a considerable height as opposed to a process of fossilisation.

"In the course of examining Lucy's humerus, it struck me that it displayed unusual kind of breaks. They are compressive breaks, a fracture which can occur in today's humans when they fall from an important height and stretch their arms to break their fall. The fractures and the position of her arms and legs suggest she was conscious when she fell and sustained these injuries", Kappelman explains. Severe other fractures that back this theory were observed in multiple skeletal elements.

These elements are consistent with the idea that Lucy had sought refuge in a high tree, and that her falling from it resulted in a tragic death. "It is likely that she was conscious when she landed from her fall, but the severity of her fractures suggests she very likely suffered severe internal damage, probably affecting every organ, and death followed swiftly", Kappelman added.

An arboreal lifestyle?

Beyond these findings – which help understand better who Lucy was as an individual – the study is important because it brings new and robust evidence that Australopithecus afarensis did spend part of its life in trees.

This debate about whether Lucy's kind was arboreal has been going on for years. Some scientists have argued that there is no evidence to support it and that the species was terrestrial, while others have said she was both arboreal and terrestrial.

"Lucy was very small, and due to the nature of her fractures, we believe it is likely that she went on top of trees at night to escape predators, much like chimpanzees do now", Kappelman says.

Lucy's fall may also highlight the fact that the adaptations that facilitated bipedal locomotion on land for Australopithecus afarensis could have had the negative effect of compromising hominids' ability to climb trees safely. This may have made them more likely to fall from heights.