Group photograph of researchers working at the Sima del Elefante fossil site, in Spain after the discovery of a hominid jaw bone dating 1.4 million years ago. Sima del Elefante site is located in the Trinchera del Ferrocarril, a trench that was dug in the foothills of Sierra de Atapuerca at the end of the 19th century. As well as a rich collection of mammal fossils dating back to between 1.25 and 1.5 million years, stone tools have been found at this site. The extensive discoveries at the Atapuerca sites have led to numerous advancements in the understanding of human evolution.