A set of fossilized footprints discovered on the Mediterranean island of Crete presents a puzzle to the story of human origins. Dated to millions of years before hominins were thought to have left Africa, their location and age challenge the established timeline of human evolution. This discovery has ignited intense debate and forced a re-examination of when the first human-like creatures may have walked the Earth.
The Trachilos Discovery
In 2002, Polish paleontologist Gerard Gierliński was on holiday in western Crete when he stumbled upon a peculiar set of markings on a rocky surface near the village of Trachilos. Initially identifying them simply as mammal prints, he recognized their potential significance. Gierliński returned in 2010 with an international team to conduct a detailed investigation of the site.
The footprints, numbering around 50, were preserved in a fine-grained sedimentary rock, which was once mud on a subtropical coastline during the late Miocene epoch. Geologists analyzed the layers above and below the footprints for foraminifera, which are tiny marine microorganisms that serve as precise markers for dating sedimentary rock.
This analysis, combined with the fact that the tracks sit just below a distinctive layer of sediment created when the Mediterranean Sea briefly dried up 5.6 million years ago, allowed researchers to establish an initial date of approximately 5.7 million years old. Subsequent studies using updated dating techniques have suggested the footprints could be even older, at around 6.05 million years.
Anatomy of the Footprints
The impressions show a foot structure with a combination of traits that are distinctly human-like. They possess a long sole, five short toes pointing forward without any sign of claws, and a large big toe, or hallux, that is in line with the other toes. This anatomical arrangement is a hallmark of bipedal locomotion, where an organism walks upright on two legs.
These characteristics stand in stark contrast to the feet of other apes, which more closely resemble a human hand. Apes have a thumb-like hallux that juts out to the side, a feature adapted for grasping branches while climbing. Instead, the Trachilos prints feature a clear ball of the foot, a structure associated with the push-off phase of a human-like stride.
When compared to the famous 3.66-million-year-old Laetoli footprints in Tanzania, the Trachilos tracks show some similarities and differences. The Cretan prints have a similarly human-like toe arrangement but a proportionately shorter sole and a narrower heel. Despite these more primitive features, the overall morphology points towards a creature that walked upright.
Implications for Human Migration
The established scientific consensus on human evolution, often called the “Out of Africa” model, posits that the human lineage originated and evolved exclusively in Africa for several million years. Fossil discoveries, including the 4.4-million-year-old Ardipithecus with its ape-like feet and the 3.7-million-year-old Laetoli tracks, have strongly supported this idea. According to this framework, the first major dispersal of hominins out of Africa did not occur until much later, around 1.8 to 2 million years ago, with the emergence of species like Homo erectus.
The Trachilos footprints fundamentally disrupt this long-held timeline. At 5.7 to 6.05 million years old, they are millions of years older than any other evidence of a hominin presence outside of Africa. Their location in Crete, which at the time was connected to mainland Greece, suggests that a creature with human-like feet was walking in Europe at the same time, or even before, some of our earliest known African ancestors like Australopithecus were living.
It could mean that early hominins evolved in Europe, or that they migrated out of Africa far earlier than any previous evidence has suggested. Another interpretation is that a separate lineage of primates in Europe developed bipedalism and human-like feet through a process known as convergent evolution, where unrelated species independently evolve similar traits.
Scientific Controversy and Alternative Explanations
The publication of the Trachilos findings was met with significant skepticism and debate within the paleontological community, as the age and location of the prints contradict the vast body of evidence pointing to an African origin for hominins. Several alternative interpretations have been proposed. One prominent argument is that the tracks were not made by a hominin at all, but by an unknown primate that convergently evolved a human-like foot.
Critics have pointed out that while the toes are human-like, other features like the narrow heel are more primitive, and some have even suggested the prints could have been made by a gorilla-like ape. The possibility that the impressions are not footprints at all, but the result of geological processes, has also been raised, though the clarity of the tracks makes this less likely for many observers.
Adding another layer to the puzzle is the fossil primate Graecopithecus freybergi, known from a 7.2-million-year-old jawbone found in Greece. Some scientists have proposed that Graecopithecus could be a pre-human ancestor, making it a candidate for the Trachilos trackmaker. However, with only dental remains, it is impossible to know what the feet of Graecopithecus looked like, leaving the identity of the Cretan trackmaker an unresolved and hotly debated scientific question.