“Lucy,” also known as A.L. 288-1, is a member of Australopithecus afarensis and is arguably the most famous fossil on the planet. She dates to 3.2 million years ago and ranks among the most completely preserved early hominin skeletons. Aus. afarensis, and Lucy in particular, preserve traits that are clearly indicative of bipedal locomotion. However, other features such as curved fingers and toes and a cranially oriented scapular joint are suggestive of arboreal behavior. A study using high resolution CT scans of Lucy’s humeri and femur and a large sample of modern chimpanzees and humans assessed relative bone strength. Results show that she is built more like a chimpanzee than a human in her relative upper limb strength, indicating that climbing behavior was a central component of her lifestyle. An additional study that also used CT scans identified distinctive axially-oriented compressive and greenstick fractures in multiple skeletal elements. The fracture edges are sharp and clean, and bone fragments along with tiny bone slivers are preserved in their post-injury positions suggesting that the fractures are perimortem in nature. Together these results indicate Lucy suffered a high energy vertical deceleration event, or impact following a fall from considerable height. Lucy has been at the center of a vigorous debate about the role, if any, of arboreal locomotion in early human evolution. It is ironic that her death can be attributed to injuries resulting from a fall, probably out of a tall tree, thus offering unusual but additional evidence for the presence of arborealism in this species.
