M.A. Martin/Archives Grupo Espeleologico Edelweis

In a cave beneath the Atapuerca hillside, and not far from Gran Dolina, lies one of the most remarkable sites in all of paleoanthropology: the location known as Sima de los Huesos, or the Pit of the Bones. The bottom of the pit is crammed with bones from such animals as cave bears, lions, foxes and wolves.

But most significantly, thousands of hominid fossils have been found here, making the Pit of the Bones the largest collection of ancient hominid fossils in the world. As a result, we know more about these early hominids than almost any others. The hominids of Sima de los Huesos lived around 400,000 years ago—much later than Homo antecessor. Detailed analysis of the Sima fossils indicates that these hominids belong to a different lineage, possibly unrelated to Homo antecessor.