Lower jaw Homo sp. 400,000 years old ©AMNH

The numerous caves in the Atapuerca region have been legendary among locals for centuries. Those brave enough to venture into the dark caverns discovered countless cave bear teeth and other animal fossils. But for many years, no one found anything other than animal bones. In 1976, however, a student looking for animal fossils discovered this early human jawbone. Since that time, scientists have unearthed hundreds of additional ancient human fossils.

In 1868, two engineers published the first scientific paper about the caves of Atapuerca. Initially, interest centered on the region’s geology because of the abundance of limestone there. The first archaeological discovery was made in 1910, when researchers uncovered a number of ancient cave paintings dating back several thousand years. But for many subsequent decades, few scholars considered Atapuerca to be significant archaeologically.

This perception began to change in the early 1970s, with the discovery of more cave paintings. Then, in 1976, a paleontology student named Trinidad Torres discovered the lower jaw above while searching for cave bear fossils in one of the caves of Atapuerca. Quickly realizing it was not from a bear, he took it to his advisor, the paleontologist Emiliano Aguirre, and together they identified it as a human jawbone—the first human fossil found at Atapuerca. Considering the kinds of animals also found at the site, Torres and Aguirre guessed that the bone was around 400,000 years old. Atapuerca suddenly became one of the most important archaeological regions in Europe.