Footprints fossilized on a beach in Crete are the real deal, researchers claim, coming from members of the extended human family. Moreover, they are even more ancient than previously reported, making them the oldest direct evidence we have of bipedalism in our ancestry, easily beating African counterparts.
In 2017 footprints near Trachilos, Crete, were claimed to be evidence of human ancestors walking upright 5.7 million years ago. This posed something of a shock, as it raised the possibility one of the most important steps in human evolution took place outside Africa.
On the principle that extraordinary claims require extraordinary proof, people questioned the dating might be wrong, or if the prints could have been caused by knuckle walkers like modern gorillas. A paper in Scientific Reports argues against the second objection, acknowledging the original dating, but only because the prints were made even earlier than first thought.
Using the magnetic polarity of the layer in which the prints were found there, and species abundance of accompanying marine organisms the paper estimates the tracks are in sediments laid down 6.05 million years ago. Only when the material was fresh would it have been soft enough to hold imprints so clearly. There is a small possibility, the authors conclude, that the prints are even more ancient than this figure, but almost none that they are actually younger.
“The tracks are almost 2.5 million years older than the tracks attributed to Australopithecus afarensis (Lucy) from Laetoli in Tanzania,” Dr Uwe Kirscher of the University of Tübingen said in a statement.
This doesn't necessarily mean hominins were walking upright in Europe before their counterparts in Africa. The species Orrorin tugenesis lived in Kenya from around the same time. Although we have found neither their footprints nor their foot bones, the shape of Orrorin femurs suggests they probably walked upright. Temporary expansion of the Sahara at the time probably prevented interchange between Europe and most of Africa, in which case upright walking may have evolved independently in both places, rather than one seeding the other.
Nevertheless, if Kirscher and co-authors are right, the work indicates we need to expand the range over which we seek the origins of human bipedality. It also tells us something about how our ancestors made the transition to upright status. "The oldest human foot used for upright walking had a ball, with a strong parallel big toe, and successively shorter side toes," said co-author Professor Per Ahlberg of the Uppsala University. All are considered features distinctive to hominins.
Today reaching Crete would require technology far beyond the early hominins, but six million years ago a landbridge connected it to the European mainland. One of the authors, Tübingen's Professor Madelaine Böhme previously discovered 7.2 million-year-old bones near Athens that have been named as a new species Graecopithecus freybergi. G. freybergi demonstrates the presence of suspected hominins in the region even earlier.
Older African ape/hominin Sahelanthropus tchadensis have been proposed as bipedal, but the authors point to evidence against this, which would make the Cretan footprints the oldest strong evidence of bipedalism in our probable ancestry we have.