Newly discovered fossil footprints challenge established theories of human evolution. The human-like footprints from Kasteli may put the established narrative of early human evolution to the test. Did our ancestors take their first steps in Crete?
Photograph of two prints possibly representing a static stance of one individual.
The footprints are approximately 5.7 million years old and were made at a time when previous research puts our ancestors in Africa — with ape-like feet.
The footprints were discovered in Kasteli by Chania on the island of Crete by paleontologist Gerard Gierlinski by chance when he was on holiday on Crete in 2002.
Gierlinski, a paleontologist at the Polish Geological Institute specialized in footprints, identified the footprints as mammal but did not interpret them further at the time. In 2010 he returned to the site together with his assistant Grzegorz Niedzwiedzki, a Polish paleontologist now at Uppsala University, to study the footprints in detail. Together they came to the conclusion that the footprints were made by hominins.
Newly discovered human-like footprints from Crete may put the established narrative of early human evolution to the test. The footprints are approximately 5.7 million years old and were made at a time when previous research puts our ancestors in Africa — with ape-like feet.
Ever since the discovery of fossils of Australopithecus in South and East Africa during the middle years of the 20th century, the origin of the human lineage has been thought to lie in Africa. More recent fossil discoveries in the same region, including the iconic 3.7 million year old Laetoli footprints from Tanzania which show human-like feet and upright locomotion, have cemented the idea that hominins (early members of the human lineage) not only originated in Africa but remained isolated there for several million years before dispersing to Europe and Asia. The discovery of approximately 5.7 million year old human-like footprints from Crete, published online this week by an international team of researchers, overthrows this simple picture and suggests a more complex reality.
Human feet have a very distinctive shape, different from all other land animals. The combination of a long sole, five short forward-pointing toes without claws, and a hallux (“big toe”) that is larger than the other toes, is unique. The feet of our closest relatives, the great apes, look more like a human hand with a thumb-like hallux that sticks out to the side. The Laetoli footprints, thought to have been made by Australopithecus, are quite similar to those of modern humans except that the heel is narrower and the sole lacks a proper arch. By contrast, the 4.4 million year old Ardipithecus ramidus from Ethiopia, the oldest hominin known from reasonably complete fossils, has an ape-like foot. The researchers who described Ardipithecus argued that it is a direct ancestor of later hominins, implying that a human-like foot had not yet evolved at that time.
The new footprints, from Trachilos in western Crete, have an unmistakably human-like form. This is especially true of the toes. The big toe is similar to our own in shape, size and position; it is also associated with a distinct ‘ball’ on the sole, which is never present in apes. The sole of the foot is proportionately shorter than in the Laetoli prints, but it has the same general form. In short, the shape of the Trachilos prints indicates unambiguously that they belong to an early hominin, somewhat more primitive than the Laetoli trackmaker. They were made on a sandy seashore, possibly a small river delta, whereas the Laetoli tracks were made in volcanic ash.
‘What makes this controversial is the age and location of the prints,’ says Professor Per Ahlberg at Uppsala University, last author of the study.
At approximately 5.7 million years, they are younger than the oldest known fossil hominin, Sahelanthropus from Chad, and contemporary with Orrorin from Kenya, but more than a million years older than Ardipithecus ramidus with its ape-like feet. This conflicts with the hypothesis that Ardipithecus is a direct ancestor of later hominins. Furthermore, until this year, all fossil hominins older than 1.8 million years (the age of early Homo fossils from Georgia) came from Africa, leading most researchers to conclude that this was where the group evolved. However, the Trachilos footprints are securely dated using a combination of foraminifera (marine microfossils) from over- and underlying beds, plus the fact that they lie just below a very distinctive sedimentary rock formed when the Mediterranean sea briefly dried out, 5.6 million years ago. By curious coincidence, earlier this year, another group of researchers reinterpreted the fragmentary 7.2 million year old primate Graecopithecus from Greece and Bulgaria as a hominin. Graecopithecus is only known from teeth and jaws.
During the time when the Trachilos footprints were made, a period known as the late Miocene, the Sahara Desert did not exist; savannah-like environments extended from North Africa up around the eastern Mediterranean. Furthermore, Crete had not yet detached from the Greek mainland. It is thus not difficult to see how early hominins could have ranged across south-east Europe and well as Africa, and left their footprints on a Mediterranean shore that would one day form part of the island of Crete.
‘This discovery challenges the established narrative of early human evolution head-on and is likely to generate a lot of debate. 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,’ says Per Ahlberg.
In their representation of their study in science magazine Elsevier, the Gierliński/Niedźwiedzki team notes among others:
“The question is whether such a range extension is credible. From a present-day perspective it seems doubtful, because the known Miocene hominin localities in Chad, Ethiopia and Kenya are separated from the north-east Mediterranean coast by the expanse of the Sahara Desert, with only the Nile valley and Levant providing a tenuous (and discontinuous) chain of mesic environments between the two. However, conditions in the Messinian were very different, with monsoonal rainfall over north-east Africa creating well-watered environments that drained northwards through the Eonile and Eosahabi (in Libya) rivers, and south into Lake Chad, which was much larger than today. There is no evidence for inhospitable environments that would have created a dispersal barrier to early hominins. We conclude that a hominin interpretation of the Trachilos footprints is not biogeographically implausible.”
Trackways. (a) Two trackways from surface B2, details shown in (b) and (c). R and L indicate right and left footprints.
Comparison with different trackmakers. Comparison of Trachilos footprint with bears (top), non-hominin primates (middle), and hominins (bottom). (a) Brown bear manus print, photo by A.A. (b) Cast of grizzly bear manus print, photo by M.L. In bears (and other Carnivora) the hallux is morphologically similar to digit 2. (c) Vervet monkey pes print, photo by G.G. (d) Lowland gorilla pes and knuckle prints, photo by Julie Dewilde. (e) chimpanzee pes print, from Meldrum et al. (2011). In non-hominin primates the hallux is morphologically distinctive but separated from the other digits by a wide gap. (f) modern human pes print, photo by G.N. (g) Trachilos footprint shown in Fig. 9b. (h) modern human foot, photo by P.E.A. (i) Archaic Homo footprint from Ileret, from Bennett et al. (2009). In hominins, the hallux is large and morphologically distinctive but positioned close to digit 2; there is also a distinct ball.
The Gierliński/Niedźwiedzki research team includes also two Greek scientists: Athanassios Athanassiou (Hellenic Ministry of Culture and Sports, Ephorate of Palaeoanthropology-Speleology) and Charalampos Fassoulas (University of Crete, Natural History Museum).