Footprints that stroll through a patchy area of Grecian beach 6 million years ago has caused researchers to rethink the timeline of hominin presence outside of Africa.

“These are perfectly [obvious] footprints,” says Per Ahlberg, a paleontologist at Uppsala University in Sweden.

If these are indeed footprints, then that would put hominins outside of Africa 4 million years before Homo erectus, which researchers have traditionally believed began to emigrate into Asia about 2 million years ago. They may also be some of the earliest bipedal prints yet discovered by a considerable margin, Ahlberg says.

Gerard Gierliński, a paleontologist with the Polish Geological Institute who typically searches for dinosaur tracks, first spotted what appeared to be human-like footprints in 2009 on a limestone surface on a shoreline in Trachilos, Crete, while on holiday. He brought in paleontologist Grzegorz Niedzwiedzki, who also came to the conclusion that they were made by a hominin.

In a 2017 study published in the Proceedings of the Geologists’ Association, Ahlberg, Niedzwiedzki, and their colleagues scanned, photographed, and analyzed the tracks. There are 29 prints in total, and all appear to be made by something walking on two legs. They range from 3.7 inches to 8.8 inches long. 

Some of them are in trackways, and some prints are individual — they appear to be milling around rather than walking in one direction. The difference in size suggests that several individuals created the tracks, possibly including adults and young individuals, for example.

The surface of the tracks differs a little in height, with three better-preserved prints on a higher surface and the majority not as well preserved on a platform a few inches lower.

The researchers dated fossilized marine organisms on the prints to somewhere between 3.5 million and 8.5 million years ago. Then, in a follow-up study published in Scientific Reports, they further constrained the date to about 6.05 million years ago.

The prints appear to be more human-like than they are like non-human apes, such as gorillas or chimpanzees. The five toes are all aligned, as they are on human feet, as opposed to the feet of chimps and gorillas, which have a big toe that sticks out to the side of the foot, similar to a thumb.

This morphology is unique for hominins from this time period. In fact, there aren’t many fossils universally accepted as hominins that date that far back. One of these is Ardipithecus kadabba from Ethiopia, with fossils dating back from 5.2 million to 5.8 million years ago. While believed to be bipedal, Ardipithecus had feet more similar to those of non-human apes, with the big toe positioned on the side of the foot.

The oldest bipedal tracks discovered before Trachilos are those at Laetoli in Tanzania, which were likely made by Australopithecus afarensis and date back about 3.6 million years ago. Those tracks appear more human-like than those made by A. kadabba, with the toes aligned on top of the foot. The tracks at Trachilos are more like those at Laetoli, though the latter have other features that appear more human-like.

Other known ape species that may have been around at the time include Sahelanthropus tchadensis, which may be a pre-hominin species known from fossils found in Chad dating to 6 million to 7 million years ago, and Orrorin tugenensis, known from fossils found in Kenya dating to about 5.8 million to 6.2 million years ago. But foot fossils from those two species have yet to be found, so it’s still unclear what made these prints.

Read More: Romanian Animal Fossils Reveal Hominin Spread Into Europe 2 Million Years Ago

Trachilos Hominins Migration

Ahlberg says that apes that predated the earliest hominins lived in Europe during the Early Miocene, when the whole area from modern-day Kinshasa to Vienna would have been covered in similar subtropical rainforest. Back then, the Sahara Desert hadn’t formed, and Europe didn’t start to get colder and more savanna-like until the Middle Miocene.            

Ahlberg says it’s possible that these hominins — perhaps all hominins — evolved in Europe, as the earliest apes began to come out of the trees when forests started to give way to drier savanna areas. If so, there should be more evidence of hominins or pre-hominins in areas between Greece and parts of Africa where similarly aged hominins have been discovered.

“If we are understanding these tracks correctly, and we had a hominin presence in the southern Balkans, realistically there would have been a hominin presence in the Levant, in Anatolia, in the Nile valley,” Ahlberg says.

Did Hominins Really Live in Europe 6 Million Years Ago?

The discovery of prints at Trachilos has been controversial right from the beginning. In fact, the team had trouble finding a place to publish their manuscript for several years due to negative peer reviews from the journals, Ahlberg says.

The main problem is that these prints are 4 million years older than the next oldest evidence of hominins outside of Africa. If they are truly hominin or even pre-hominin, and truly that old, the Trachilos footprints would rewrite everything that we know about hominins outside of Africa.

Doubts arose about the source of the prints almost immediately. However, a bigger challenge arose in 2022, when another study published in Scientific Reports disputed the dates of the footprints by Willem Zachariasse and Lucas Lourens, suggesting that the marks were more likely 3 million years old, from the Late Pliocene. If so, those authors contend, Crete would have already been an island.

Part of Ahlberg’s argument is that in the Miocene, Crete wouldn’t have been an island. The Aegean Basin hadn’t yet subsided, so the area would have been near the southern end of the Balkan Peninsula — easy enough for any hominins on mainland Europe to walk to. 

But if Zachariasse and Lourens are right about the age of the footprints, then Crete would have been at least 100 kilometers (about 62 miles) away from the nearest mainland — difficult to reach at this time. 

“The improbability that Late Pliocene hominins were able to sail across 100 kilometers [of] open sea from the nearest European mainland to Crete therefore raises questions such as who made the ichnites and are they ichnites at all,” Zachariasse and Lourens write about the footprints, also known as ichnites. “These questions call for a re-investigation of the bedding surface phenomena described as hominin-like footprints.”

These researchers don’t offer any alternative explanation for what might have made such footprint-looking marks. Ahlberg, for his part, is now working with his colleagues to reexamine the region’s geology, but he says the early results suggest that some of Zachariasse and Lourens’ findings are incorrect. 

“Once our own data have been fully interpreted, we will have a detailed understanding of the geology of the site, and we will then see whether the age estimate has to be adjusted,” Ahlberg says.

In considering the long history of hominin evolution, Ahlberg also points out that there is little evidence that any hominins, or pre-hominins, that may have been in Greece persisted. The species perhaps moved back to Africa as weather cooled, or these lineages died out, until 2 million years ago when Homo erectus began to emigrate into Asia.

Read More: Two Different Early Human Species Walked the Same Lake 1.5 Million Years Ago

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Joshua Rapp Learn is an award-winning D.C.-based science writer. An expat Albertan, he contributes to a number of science publications like National Geographic, The New York Times, The Guardian, New Scientist, Hakai, and others.