Hand axe Quartzite 400,000 years old photo D. Finnin/AMNH

In all the years of excavating the Pit of the Bones, researchers had never uncovered anything other than fossils. Then in 1998, scientists made a major discovery: a stone hand axe, mixed in the mud with the bones of the Sima humans.

Similar tools dating back to the time of the Sima humans have been recovered from nearby locations, such as the Galeria site, also in the railway trench, just 50 meters (160 feet) from Gran Dolina. This new tool from Sima, however, may have important behavioral implications: these hominids made the hand axe from a very unusual raw material source. The scientists who discovered the tool have suggested that the Sima hand axe may have been intentionally deposited with the Sima humans in the Pit of the Bones.

Investigators have been able to piece together a tremendous amount of information about the Sima humans—even identifying the diseases or injuries that may have killed them. But they had to make educated guesses about what tools the Sima humans used based on the implements found at other sites from the same time. How this implement came to be in the cave—and why no other tools have been found—is still a mystery.

In contrast to the simple stone tools made by Homo antecessor, this large hand axe (classified as a Mode 2 tool) is quite sophisticated. It was carefully shaped on both sides, probably from a large core. Whoever made this symmetrical hand axe had a predetermined shape in mind when removing flakes to form the tool. These characteristics indicate that this is a Mode 2 artifact.