The first remains of the last common ancestor of modern humans and Neanderthals - Homo antecessor - were discovered at the Atapuerca site in Burgos (Castilla y León) on 8 July 1994.
Over the next twelve months, more than 80 bone fragments from six individuals, which included a child who had died at about ten years of age, were discovered.
Atapuerca, declared a World Heritage Site by Unesco in 2000, is a set of archaeological and paleontological sites that contain some of the oldest human remains on the Iberian Peninsula.
The important discovery was made at the Gran Dolina site, thought to be the most important in Europe, due to the abundance and diversity of its remains.
The archaeological significance of this region became apparent during the construction a railway line built in the 19th century. The line, now disused, ran through the Atapuerca mountains.
The remains of the child, which mainly consisted of a skull, has since become known as the Gran Dolina child.
The fossilised bones were discovered by Spanish archaeologist Aurora Martín Nájera, who, since its inception in 2010, has been the general coordinator of the Museum of Human Evolution in Burgos.
Archaeologists also unearthed around 200 stone tools and hundreds of animal bones, all of which were believed to be at least 800,000 years old.
The find changed the general conception concerning human evolution on the European continent. Because of the characteristics of their forehead and teeth, the archaeologist first believed that the remains resembled Homo heidelbergensis, predecessor of the Neanderthal man. However, they also presented more modern characteristics, such as facial features typical of Homo sapiens; therefore, they were identified as the common ancestor of both.
Researches were also able to perceive that these hominid primates practised cannibalism due to the marks found on the bones, which suggested a process of dismemberment and extraction of meat.
The remains are believed to be at least 250,000 years older than any other hominid discovered in western Europe, although the classification of the remains is still being debated by some researchers.