We share plenty of features with apes, but the shape of our feet isn't one of them. So that makes the discovery of human-like footprints dating back 5.7 million years – a time when our ancestors were thought to still be getting around on ape-like feet – a surprising one. Further confounding the mystery is the fact that these prints were found in the Greek islands, implying hominins left Africa much earlier than our current narrative suggests.
Fossilized bones and footprints have helped us piece together the history of human evolution. One of the earliest hominins – ancestors of ours that are more closely related to humans than chimps – was a species called Ardipithecus ramidus, which is known from over 100 specimens. Living about 4.4 million years ago, it had an ape-like foot, with the hallux (the big toe) pointing out sideways rather than falling in line like ours. Fast-forward about 700,000 years, and a set of footprints from Laetoli in Tanzania shows that a more human foot shape had evolved by then.
Enter the newly-discovered footprints. Found in Trachilos in western Crete, they have a distinctly human-like shape, with a big toe of a similar size, shape and position to ours. They appear to have been made by a more primitive hominin than the creature that left the Laetoli prints, but there's a problem: they also predate Ardipithecus by about 1.3 million years. That means a human-like foot had evolved much earlier than previously thought, throwing a spanner into the accepted idea that the ape-footed Ardipithecus was a direct human ancestor.
These footprints were fairly clearly dated to the Miocene period, about 5.7 million years ago. According to the researchers, they lie in a layer of rock just below a distinctive layer that formed when the Mediterranean sea dried out, about 5.6 million years ago. To further back up the dating, the team analyzed the age of marine microfossils from sections of rock above and below the prints.
But the age of the Trachilos tracks isn't the only mysterious feature about them: where they were found is also key. Until recently, the fossil record suggested that hominins originated in Africa and didn't expand into Europe and Asia until about 1.8 million years ago. But these prints indicate that something with remarkably humanoid feet was traipsing through Greece millions of years earlier than conventional wisdom holds.
Interestingly, this find lines up with another recent discovery that could rewrite human history. Back in May, a study described 7 million-year-old bones of a hominin species called Graecopithecus freybergi, which were discovered in Greece and Bulgaria. That find represented such a huge discrepancy from the current thinking that the researchers pondered whether it meant that the human and chimp branches of the family tree originally split in Europe, and not Africa. The new study might correlate that conclusion.
"This discovery challenges the established narrative of early human evolution head-on and is likely to generate a lot of debate," says Per Ahlberg, last author of the paper. "Whether the human origins research community will accept fossil footprints as conclusive evidence of the presence of hominins in the Miocene of Crete remains to be seen."
The research was published in the journal Proceedings of the Geologist's Association.
Source: Uppsala University