? WHO OWNS THESE 300,000 YEAR OLD FOOTPRINTS
During their research on human evolution, paleoanthropologists usually focus on fossilized bone remains. However, another type of vestige is increasingly used: the footprints left by our ancestors and preserved over time.
Unlike bone remains, footprints provide a window into brief moments in the life of extinct individuals. By this very particular time scale, their study provides a lot of new information on locomotor behavior but also the composition of groups that lived hundreds of thousands or even millions of years ago. Unfortunately, fossil footprints are particularly rare due to their fragility. When they are discovered, a real investigative work begins.
Photograph of the archaeological site at the foot of the Asperillo cliff in Spain.
E. MayoralWhen these footprints were first studied, published in the journal Scientific Reports in 2021 , we showed that they were left by a group of children, teenagers and adults. In order to estimate the age of individuals from their footprints, we used experimental data . Participants of varying ages had left footprints in soil similar to that of Doñana. The footprints were then measured and statistical relationships were established between the dimensions of the footprints and their biological characteristics such as their size or their age. These relationships were then applied to the fossil footprints that had been measured.
Moreover, the orientation of these footprints towards animal tracks (birds, deer, cattle, etc.) suggested possible hunting behavior on the part of this prehistoric group.
One of the questions was which human species had left these footprints. In most cases footprints are not associated with a species on the basis of anatomical criteria, as are the fossil bone remains, but from the chronological context. This is why we attributed these footprints to Neanderthals on the basis of the only available temporal reference, a date of 106,000 years obtained during a study of the site in the mid-2000s. Such an attribution was justified because the Neanderthals were the only known species to occupy the Iberian Peninsula and more widely Western Europe at this date.
NEW DATES
However, while continuing the study of this site, we proceeded to a sampling of the soil where the footprints were discovered in order to obtain more precise datings. The results of this study published in October in the journal Scientific Reports are surprising: the soil is not dated 106,000 but 296,000 years. The prints are therefore much older than estimated. This difference in the dates obtained is not only due to the methodological advances in the techniques used but also to the position of the dated samples focusing more on the level of the footprints than the very first datings which had previously been used.
Footprint discovered in Doñana compared to an adult foot.
E. MayoralThe new dating placed the footprints in a new geographical and environmental context. The continent of Europe was on the verge of drastic climate change 300,000 years ago . Relatively warm conditions gave way to much colder conditions, a precursor to an ice age. At that time, the sea level on the European continent was on average 60 meters below its current level. The coastline of southwestern Spain was then 20 or 25 kilometers offshore from its present position.
In addition to these environmental and geographical changes, this new chronology is at the origin of an essential question: did Neanderthals really make these footprints?
NEW SUSPECTS
To answer this question, it was necessary to look into the paleontological records to find out which species was present 296,000 years ago during the period called the Middle Pleistocene. According to paleoanthropologists, individuals who lived during this time belonged to the "Neanderthal lineage". A “lineage” like the “Neanderthal lineage” or the famous “human lineage” is made up of several related species. The "Neanderthal lineage" is thus composed of Neanderthals, also called Homo neanderthalensis , and an older species, Homo heidelbergensis , some of which would be the origin of Neanderthals.
Unfortunately, fossil bone remains from this period are relatively poor and dispersed not only temporally but also geographically. They show, however, that the earliest Neanderthals and the latest Homo heidelbergensis were both present in Europe when the Doñana footprints were made. The other sites where footprints have been found aren't much help. Indeed, in all of the European Middle Pleistocene, only four sites yielded footprints: Terra Amata in France (380,000 years old), Roccamonfina in Italy (345,000 years old), Biache-Vaast in France (236,000 years old) and Theopetra in Greece (130,000 years). While the footprints of the first two sites have been attributed to Homo heidelbergensis, those of the next two have been assigned to Homo neanderthalensis .
The presence of two species in Europe during this period makes it difficult to attribute the Doñana footprints to one or the other of these species. One option would be to compare the characteristics reflected by the footprints to the anatomy of the feet of the two species to find out which species they most closely resemble. However, the remains of feet dating from the Middle Pleistocene are little known. They are almost all from the Spanish site of Sima de Los Huesos near Atapuerca and related to Homo neanderthalensis. Moreover, these remains are very fragmentary and no complete foot has yet been found. Furthermore, the morphology of a footprint does not only result from anatomical characteristics but also from other factors such as the nature of the soil (its humidity, its grain size, its mineralogy, etc.). It is therefore rare to find footprints reflecting perfectly preserved anatomical characteristics (traces of the toes, arch of the foot, etc.), even more so in dune environments such as Doñana where the footprints can be damaged and destroyed by the action of wind and tides.
The assignment of these footprints to either species is also complicated by the lack of consensus among paleoanthropologists regarding the Neanderthal lineage and the definition of Homo heidelbergensis . Various models of evolution have been proposed, but this question is still far from being resolved, given the paucity of the fossil record and the complexity of the evolutionary relationships highlighted by the latest studies of ancient DNA.
Thus, the footprints of Doñana were probably left by individuals belonging to the Neanderthal line. Who of the Neanderthals or their related ancestors, the Homo heidelbergensis , left these traces is still an open question. Despite these uncertainties, the Doñana site completes our knowledge of human occupations in Europe during the Pleistocene and our evolution.
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