A little over a year ago, at the foot of the Asperillo cliff, on the coast of the Doñana Natural Area (Huelva), we revealed a large area where, along with numerous animal tracks, other human tracks appeared. It was about hominin footprints.
Until then, the only time reference that allowed framing the age of the site was the dating of one of the dunes that covered the surface. This placed it at about 106-000 years (Upper Pleistocene). As with most hominid footprints found around the world, taxonomic attribution was based solely on chronological context. For this reason, Neanderthals became the main suspects.
However, throughout the normal development of the investigation, both the surface itself where the footprints appeared, never dated before, and the dunes located above were sampled. The surprise arose when the dune that covered the surface gave values around 275,000 years. And most surprisingly, the age of the surface with the hominin footprints turned out to be about 295,800 years (Middle Pleistocene). This new chronology radically changes many of the hypotheses initially raised.
The new dating placed the footprints in a new geographic and environmental context. 300,000 years ago, the European continent was preparing to attend drastic climate change. Relatively warm conditions were changing to much cooler ones, the harbingers of an ice age. At that time, the sea level on the European continent was on average about 60 meters below the current level, which means that the Huelva coastline would be between 20 and 25 kilometers offshore from its current position.
In other words, the coastal plain was very extensive and probably of fluvio-deltaic origin. It is likely that it was covered by water during wet seasons and fully or partially exposed during dry seasons.
Hominid footprints originally attributed to Neanderthals from Matalascañas beach
It is in this shallow and even hypersaline lacustrine environment that polygonal soils covered by microbial mats were formed that were trampled by both hominids and the rest of the fauna. Today this type of polygonal mat network is found in extensive areas of marshland in both hot desert and tropical climates.
In the non-flooded areas of this broad coastal plain, more or less extensive vegetated areas would be found. Around them would extend an important development of dune systems that would move inland from the coast.
New suspects?
The environmental context and the landscape have changed with respect to the initial interpretation. Have the producers of these prints also changed? The answer is to be found in the paleontological record.
During the Middle Pleistocene hominin fossils are attributed to the Neanderthal lineage: homo neanderthalensis y A man from Heidelberg. However, their remains are still very scarce, fragmentary and geographically dispersed. And what is worse, the traces are even scarcer than the skeletal remains in all of Middle Pleistocene Europe. Only four sites have provided traces of this period: Terra Amata (380,000 years), Roccamonfina (345,000 years, attributed to A man from Heidelberg), Biache-Vaast (236,000 years, homo neanderthalensis) and Theopetra (130,000 years, homo neanderthalensis).
On the other hand, it must be considered that the morphology of the footprint is not only the result of the anatomy of the foot, but also of other factors such as the biomechanical characteristics, the type of substrate and the processes that gave rise to the fossil. For this reason, the tracks studied must be well preserved and reflect various anatomical features (finger impression arc), which rarely occurs in loose substrates such as Matalascañas, where morphological variation is very important.
To support a reliable taxonomic assignment, its anatomical characteristics should be compared with the known skeletal record for the Middle Pleistocene.
Almost all known foot fossils for that period come from the Sima de Los Huesos site (Atapuerca, Spain) and are associated with individuals related to Neanderthals. Even a more precise attribution seems complicated, since there are many debates about the evolution of this lineage, but also about the taxonomic definition of A man from Heidelberg.
Different models have been proposed for the evolution of the Neanderthal lineage, but this question is still far from being resolved, given the paucity of the fossil record and the new and more complicated evolutionary picture provided by the latest studies of ancient DNA. Furthermore, not all anatomical features evolved at the same rate and polymorphisms probably occurred in different features with different percentages of appearance.
Despite these uncertainties, the Doñana site appears to be a crucial record for understanding human occupation in Europe during the Pleistocene.
This article was originally published on ‘The Conversation’.