Aug. 31 (UPI) -- Researchers have found 5.7 million-year-old, human-like footprints in Crete, complicating the story of human evolution.
A significant body of paleontological evidence suggests early humans diverged from their ape ancestors in Africa. A set of footprints found in Tanzania suggest hominins, the earliest human relatives, were walking upright some 3.7 million years ago.
Most researchers believe these first pre-humans evolved in southern and eastern Africa, remaining on the continent for several million years before migrating to Europe and Asia.
The discovery of human-like feet in Crete complicates the narrative.
While the famed Laetoli footprints of Tanzania are clearly human-like, researchers argue other famed African tracks, like ones found in Ethiopia, are more ape-like than the those uncovered in Crete.
The newly discovered "Trachilos" tracks are unmistakably human-like, researchers say. The prints showcase a human-like big toe and the ball shape found on the sole of human feet.
"What makes this controversial is the age and location of the prints," Per Ahlberg, a paleontologist at Uppsala, said in a news release.
Until recently, no hominin fossils older than 1.8 million years had been discovered outside of Africa.
Earlier this year, scientists claimed a set of 7.2 million year old chimp fossils found in Bulgaria and Greece actually belonged to the oldest human-ape relative, dubbed Graecopithecus -- the first hominin to split from the ape lineage.
The researchers argued the chimp-human split may have first occurred in Southern Europe, not Africa, with apes and hominins becoming separated as savannas spread across Southern Europe and deserts expanded across North Africa and the Mediterranean.
But the evidence of early humans evolving in Europe remains scant. A jaw bone, teeth and some footprints are dwarfed by an extensive collection of fossils belonging to African hominins like Homo naledi and Homo floresiensis.
As some critics pointed out in the wake of the Graecopithecus claim, determining whether a fossil or anatomical anomaly confirms a divergence between apes and humans is exceedingly difficult. Furthermore, many species can independently evolve traits -- a phenomenon called parallel evolution.
"This points to why the new claims about Graecopithecus need to be treated with a good deal of caution," Australian researcher Darren Curnoe wrote in May.
The same skepticism should likely be applied to the newly discovered Trachilos tracks.