Date: August 31, 2017
Source: Uppsala University
Summary: 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.
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 millon 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.
