Prehuman footprints six million years ago

For a long time it was clear that the cradle of man and his closest ancestors was in Africa. However, fossil finds and footprints discovered in Greece in recent years suggest that potential human ancestors may have existed in Europe as well. When exactly the prehuman footprints found in Crete were formed, scientists have now investigated in more detail. Their result: Human-like footprints are already 6.05 million years old and therefore may be the oldest evidence of the existence of a bipedal walking hominid.

Be it Australopithecus afarensis, Ardipithecus or Homo habilis: Most of the ancestors of humans lived in Africa and developed there from prehistoric monkeys living in trees to bipedal prehumans and later to the first members of the genus Homo. According to the current theory, these first people emigrated from Africa and also settled on other continents. But in recent years, scientists in the Eastern Mediterranean have discovered fossils and footprints that do not seem to fit this scenario. These include the approximately 7.2 million-year-old lower jaw and the tooth of Graecopithecus freybergi, an early prehuman discovered in Greece and Bulgaria in 2017.

Traces with human features

Also in 2017, the research team found footprints in Trachilus, Crete, which first date must have formed more than five million years ago – and which exhibited some strikingly human-like features: “The morphology contains features previously thought to be unique to hominins, in including the front part of the metatarsus, a tight and solid big toe that lies parallel to the other toe, and the side toes are becoming increasingly shortened, ”explains Uwe Kirscher from the University of Tübingen and his colleagues. These human traits were combined with some primitive traits such as the absence of a longitudinal arch, a shorter sole and a heel that is not yet as wide and pronounced as in modern humans. According to some researchers, this combination of appearance and age suggests that these footprints must have come from a prehuman predecessor of Australopithecus. But that would mean that the prehumans already existed in Europe more than five million years ago.

So far, however, this scenario is very controversial and several alternative explanations for the human appearance of footprints have been proposed. According to some scientists, the original monkey, and therefore non-hominins, may have left such traces as well, as some characteristics can still be found in gorilla footprints. Other anthropologists have denied this, pointing to some fairly distinct differences. Another problem arises when interpreting the Trachilus traces: their exact age has so far been difficult to determine because the sequence of layers on the site is incomplete, and the fossil plankton dating in the sediments below the traces ranges from 8.5 to 8.5 years. years . Therefore, Kirscher and his colleagues re-examined the stratigraphy and microfossils and re-dated the trace layer using chemical, mineralogical and isotope analyzes.

The oldest traces of pre-man

Analyzes have shown that Trachilos footprints formed around 6.05 to 6.06 million years ago. “The footprints are therefore almost 2.5 million years older than the footprints from Laetola, Tanzania, attributed to Australopithecus afarensis (Lucy),” says Kirscher. In addition, the prints in Crete are roughly as old as the fossils of the hominina Orrorin tugenensis from Kenya. His fossils, discovered in 2001, and especially the femurs, suggest that this primal primate could have walked upright and therefore may have been one of human ancestors. However, no footprints have survived from Orrorin. The still unknown primate that left its mark on the sand of a beach in Crete may therefore have left the oldest known prehuman footprints, the research team explains.

If the dating of footprints and their prehuman origin is confirmed, it will also shed new light on the early evolution of human walking more than six million years ago. For if you put these footprints and the fossils of the 7.2-million-year-old Graecopithicus together, the eastern Mediterranean could be one of the centers of human evolution, as could East Africa. According to a team led by senior author Madeleine Böhme of the University of Tübingen, climate change in the Sahara region may have caused preforms of monkeys and humans to move back and forth between Africa and Eurasia. During the desertification phase of 6.25 million years ago, European mammals and possibly apes could have migrated to Africa via Mesopotamia. Then, when the Sahara dried up, it created a barrier and thus initiated the separate but partially parallel evolution of the African prehuman Orrorin tugenensis and the European prehuman – this is the hypothesis of Böhme and her colleagues. However, there is still no clear evidence of this.

Source: Uwe Kirscher (Eberhard Karls University of Tübingen) et al., Scientific Reports, doi: 10.1038 / s41598-021-98618-0

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