One of the most famous fossils in human evolutionary history is at the center of a new scientific debate. The fossilized skeleton dubbed “Lucy” was part of an extinct species called Australopithecus afarensis, an early relative of Homo sapiens who was among the first hominins to walk upright. She died 3.18 million years ago, and her remains were discovered in the early 1970s in Ethiopia. Her skeleton is complete enough to give us a good picture of her anatomy, which is part of what led to the current controversy. A study published in Nature this week suggests that a careful analysis of her bones reveals how she died—by falling to her death from a very tall tree. But other scientists say the evidence is thin at best.

University of Texas-Austin anthropologist John Kappelman and his team did a complete X-ray CT scan on Lucy’s bones, allowing them to create high-resolution 3-D renders as well as 3-D printouts of her skeleton. By comparing the way her bones had fragmented with contemporary X-rays from people who fell, they came to the conclusion that the fragmentation of her leg bone was “green,” that is, it took place right before she died.

Kappelman and his colleagues write, “Although the fractures in Lucy’s humeri provide evidence that she was conscious when she stretched out her arms in an attempt to break her fall, the severity of the numerous compressive fractures and presumed organ damage suggest that death followed swiftly.” It appears that the joint in her leg suffered from extreme compression of the type you’d expect in somebody who fell on their feet from a great height, out of a local tree where nests might be as many as 23 meters off the ground. (They estimated this height based on the typical heights of chimpanzee nests today.)