Who owns these 300,000-year-old footprints?

Unlike skeletal remains, footprints provide a window into the lives of extinct individuals. Because of this very specific time scale, their study provides a wealth of new information about locomotor behavior, as well as 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, the real investigative work begins.

In 2020, 87 footprints were discovered at the foot of the Asperillo Rock on the coast of the Doñana Natural Area in southwestern Spain.

Photograph of an archaeological site at the foot of the Asperillo Rock in Spain. E. Mayoral, Provided by the author

In the first study of these footprints published in the journal Scientific Reports In 2021, we showed them being abandoned by a group of children, teenagers and adults. We used experimental data to estimate the age of individuals from footprints. Participants of various ages left footprints in the soil like Doñana. The footprints were then measured and statistical relationships were established between the dimensions of the footprints and biological characteristics such as their size or age. These relationships were then applied to the measured fossil footprints.

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Furthermore, the alignment of these footprints with animal tracks (birds, deer, cattle, etc.) suggested possible hunting behavior of this prehistoric group.

One of the questions was what kind of human left these footprints. In most cases, footprints are associated with a species from a chronological context rather than based on anatomical criteria, such as fossil bone remains. That is why we attributed these footprints to Neanderthals based on the only available provisional reference of 106,000 years, which was obtained during a survey of the site in the mid-2000s. Such an attribution was justified because Neanderthals were the only known species. occupying the Iberian Peninsula and more broadly Western Europe at this date.

new dates

However, as we continued to investigate this site, we began sampling the soil where the footprints were found to obtain more accurate dates. The results of this study were published in the journal in October Scientific Reports surprising: the earth is not 106,000, but 296,000 years old. Therefore, the traces are much older than expected. This difference in the dates obtained is due not only to methodological advances in the techniques used, but also to the position of the dated samples, which focus more on the level of traces than the first dates used earlier.

A footprint found in Doñana compared to a mature foot. E. Mayoral, provided by autEuro

The new dating placed the tracks in a new geographic and ecological context. The European continent was on the brink of a drastic climate change 300,000 years ago. Relatively warm conditions gave way to colder conditions that heralded the Ice Age. At that time, the sea level on the European continent was on average 60 meters lower than its current level. The coastline of southwestern Spain was then 20 or 25 kilometers offshore from where it is today.

In addition to these environmental and geographic changes, this new chronology raises an important question: Did Neanderthals really leave these footprints?

New suspects

To answer this question, it was necessary to look at the paleontological record to find out what species existed during the so-called Middle Pleistocene, 296,000 years ago. According to paleoanthropologists, the individuals who lived in this period belonged to the “Neanderthal generation”. A ‘lineage’, such as the ‘Neanderthal line’ or the popular ‘human line’, consists of several related species. The “Neanderthal lineage” consists of so-called Neanderthals Homo neanderthalensisand an older species, Homo heidelbergensissome are believed to be Neanderthals.

Unfortunately, bone remains from this period are relatively poor and not only temporally but also geographically dispersed. However, they show that the first Neanderthals and the last Homo heidelbergensis Both were present in Europe when the Doñana footprints were made. Other footprint sites don’t help much. Indeed, only four sites have yielded footprints in the entire European Middle Pleistocene: Terra Amata in France (380,000 years), Roccamonfina in Italy (345,000 years), Biache-Vaast in France (236,000 years) and Theopetra in Greece (130,000 years). The footprints of the first two sites are attributed Homo heidelbergensisattributed to the next two Homo neanderthalensis.

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The presence of two species in Europe at this time makes it difficult to attribute the Doñana footprints to one or the other of these species. One option would be to compare the features the footprints reflect with the anatomy of the feet of the two species to see which species they most resemble. However, foot fossils from the Middle Pleistocene are poorly known. Almost all come from and are related to the Spanish site of Sima de Los Huesos near Atapuerca Homo neanderthalensis. Moreover, these remains are very fragmentary and a complete leg has not yet been found. In addition, footprint morphology is a result not only of anatomical features, but also of other factors such as the nature of the soil (its moisture content, grain size, mineralogy, etc.). Therefore, footprints showing perfectly preserved anatomical features (toe prints, arch of the foot, etc.) are rare, especially in sandy environments like Doñana, where footprints can be damaged and destroyed by wind. the tides.

Assigning these footprints to either species is also complicated by the lack of consensus among paleoanthropologists on the definition of Neanderthal lineage and lineage.Homo heidelbergensis. Various evolutionary models have been proposed, but the question remains far from settled, given the paucity of the fossil record and the complexity of evolutionary relationships highlighted by the most recent studies of ancient DNA.

Thus, Doñana’s footprints were probably left by Neanderthals. By knowing which of the Neanderthals or their related ancestors, Homo heidelbergensis, it is an open question that you leave traces. Despite these uncertainties, the Doñana site adds to our knowledge of human occupations and evolution in Europe during the Pleistocene.

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