Press Backgrounder: "Ardipithecus"
• Prepared by the Middle Awash paleoanthropological research project
• Accompanies October 2 special issue of the journal Science.
EMBARGOED FOR RELEASE UNTIL:
5:30 PM Ethiopian time
10:30 A.M. Eastern Time (U.S.) on October 1.
OLDEST HOMINID SKELETON UNVEILED
Family Roots: Ardipithecus
New Evidence for Human Evolution
Not from Chimpanzees
ADDIS ABABA, ETHIOPIA: Scientists working in the Afar Rift, Ethiopia, have
published new results of a 17-year investigation of the 4.4. million-year-old hominid
Ardipithecus ramidus in the October 2 special issue of the journal Science.
These results open a new chapter on human evolution by extending knowledge into a
previously poorly known period, only a few million years after the human line diverged
from that leading to chimpanzees.
The findings reveal the kind of human ancestor that came before the better-known "apeman" Australopithecus, until now the most completely known early hominid genus
thanks to fossils like the skeleton of "Lucy" discovered in Ethiopia in 1974. The new
fossils reveal the early evolutionary steps that our ancestors took after we diverged from
our common ancestor with chimpanzees.
The centerpiece discovery is a 4.4 million-year-old partial skeleton of a female
nicknamed "Ardi." The team recovered important parts of the skeleton including the
skull with teeth, arms, hands, pelvis, legs, and feet.
This is now the earliest skeleton known from the human branch of the primate family
tree. Our branch constitutes the zoological family "Hominidae;" "hominids" include
Homo sapiens as well as all species closer to humans than to chimpanzees and bonobos,
our closest living relatives. The discoveries provide new insights into how hominids
might have emerged from an ancestral ape.
BACKGROUND TO THE DISCOVERIES
Until now, the earliest well-known stage of human evolution was Australopithecus, the
small-brained but fully bipedal "ape-man." Australopithecus is known by several species
that lived between ~ 4 and ~1 million years ago. The most famous fossil of
Australopithecus is the 3.2 million-year-old partial skeleton of a female Australopithecus
afarensis nicknamed "Lucy," found in 1974. The new Ardipithecus ramidus skeleton and
associated finds are older and more primitive than Australopithecus.
The genetic similarity of humans and chimps led to the expectation that when earlier
hominids were found, they would converge towards a chimpanzee-like anatomy. The
Ardipithecus ramidus fossils do not.
WHAT WAS FOUND
Who found what, and when?
• The first Ardipithecus fossil (a single upper molar) was found by Dr. Gen Suwa in
1992. The species Ar. ramidus was first named in 1994 (in Nature) on the basis of this
and other fragments found nearby.
• Then, on November 11, 1994, Yohannes Haile-Selassie found the first piece (hand
bone) of the new Ardipithecus skeleton. This skeleton was recovered through careful
excavations between 1994 and 1997.
• The skeleton is partial, its bones disarticulated and scattered, with larger elements often
having been broken into smaller pieces prior to being covered with sediment. More than
125 pieces of this individual were found.
• Estimation of the "percentage" representation of a skeleton is not very meaningful, but
the most important parts of any early hominid skeleton are the skull, teeth, arms, hands,
pelvis, legs, and feet. All these were recovered for this individual, but many of the larger
elements were damaged and required restoration.
• The team found many other fossils of other individuals of the same hominid species, a
total of 110 specimens representing a minimum of 36 different individuals, including
youngsters, males, and females (of which the "Ardi" skeleton is only one; ARA-VP6/500 is her catalog number). As in many fossil assemblages, teeth are common.
• The team also found thousands of bones from dozens of animal and plant species,
many new to science, and all informative about "Ardi's" environment.
Why the name?
• The genus and species names are derived from the local Afar language. "Ardi" means
"ground," and "pithecus" is Greek for ape (and is traditionally used in early hominid
names, even though the word is technically a misnomer since all these are hominids and
not apes). "Ramid" means root.
• A literal translation of Ardipithecus ramidus would be "root of the ground ape." It turns
out to be a pretty good name for the species, since our analysis concludes that
Ardipithecus ramidus was partially arboreal and partially terrestrial, and preceded the
more fully terrestrial Australopithecus and Homo.
DIMENSIONS OF THE RESEARCH EFFORTS
Some of these fossils were found early the 1990s. Why so long between discovery
and publication?
• In order to collect all the data necessary to interpret the fossils, the team did intensive
fieldwork at and around Aramis over 11 different field seasons between 1981 and 2004;
their last field observations were made in 2008.
• Because the Aramis localities are so extensive--transecting an ancient landscape
exposed along a 9 km strip--they provided an avalanche of new geological and
paleobiological data. A large expert team was assembled, with specialists from many
different countries and disciplines, in order to properly extract and study all of the
available data.
• Because of the abundance of information, each group of plants and animals had to be
recovered through fieldwork, and then analyzed in Ethiopia and many other laboratories
throughout the world.
• Because of "Ardi's" completeness and particularly poor fossilization, great care had to
be taken in preparing the fossils for handling, and then molding, photographing,
reconstructing, and conducting comparisons with other fossil and modern ape species.
• Many specialized techniques and instruments were used in the analysis, ranging from
mass spectrometers (to measure the age of the rocks, and composition of isotopes of the
tooth enamel and soil carbonates), to micro-CT scanners (to restore and study the inner
and outer anatomy of the bones and teeth), to scanning electron microscopes (to study
structure and surface details of bone and teeth). Obtaining and processing just the
Ardipithecus CT scans took thousands of hours. Many more were spent gathering and
analyzing comparative modern ape and human materials.
How many people were involved in the discoveries and subsequent research?
• Hundreds of people have worked at Aramis with the project since 1992.
• A total of 47 different scientists representing 10 countries and many different research
areas of paleontology and geology worked together to author the 11 scientific papers.
GEOGRAPHY
Where were the finds made?
• The new fossils were found in the Middle Awash study area in Ethiopia's Afar Rift,
about 140 air miles (230km) northeast of Addis Ababa, Ethiopia's capitol. They are from
the Aramis area, a several-km wide drainage catchment that stretches for about 10 km.
Aramis is located about 75 km S. of the discovery location for the 3.2 Ma hominid
nicknamed "Lucy" in 1974, and formerly the world's oldest hominid skeleton.
• Today the Middle Awash area is inhabited by the Afar people who are semi-nomadic
pastoralists living in a harsh desert environment. One of the small Afar villages next to
the modern Awash River is named Aramis. People from this and adjacent settlements
worked with the scientists to recover the fossils.
Why here? Is this the "Cradle of Humankind?"
• As the Arabian peninsula has drifted away from Africa over many millions of years,
the Red Sea and Gulf of Aden rifts formed and filled with seawater. Africa's Great Rift
Valley intersects these two other flooded rifts to form a large triangular depression called
the Afar Rift, in Ethiopia.
• For millions of years, sediments have been accumulating in this depression. Much of
Africa has a high elevation and most surfaces are eroding. This is why fossils are
concentrated in the rift valleys of Tanzania, Kenya, Ethiopia, and other African countries.
• The distribution of plants and animals found today as fossils in eastern Africa,
including hominids, is therefore a fortunate accident of geology and where these
organisms used to live. Ethiopia is particularly fortunate to have so many accumulated
sediments. Combined with the country's manpower development and infrastructure
(including a massive new laboratory complex for antiquities research and stewardship),
Ethiopia has now taken the lead in human origins studies and discoveries.
GEOLOGY AND GEOCHRONOLOGY
• Dr. Giday WoldeGabriel of Los Alamos National Laboratory led the field geology
investigations and sampling of stratigraphic markers of lavas and ashes. Laboratory
analyses of these provided the dates that bracket the fossils.
How old are the fossils?
• At Aramis, modern erosion has exposed a total thickness of ~300 m of ancient lake,
river, and stream deposits with interbedded volcanic rocks. The base of the local
sedimentary succession around Aramis is dated to ~5.6 Ma, and the top to ~3.9 Ma.
• At Aramis, the Ardipithecus fossils were concentrated in a 3-6 m horizon of sediments
laid down on an ancient floodplain. To date their carefully selected samples of the
volcanic layers sandwiching the Ardipithecus fossils, the team used the single crystal,
argon-argon (40Ar/39Ar) laser heating method. The 4.4 Ma dates they got for both
volcanic horizons were confirmed by measurements of the magnetic polarity of the
sediments, and by biochronological analysis of associated vertebrate fossils.
• Professor Paul Renne of the Berkeley Geochronology Center led the 40Ar/39Ar and
paleomagnetic laboratory work. This dating technique is a highly accurate method that
can determine the time that has elapsed since the eruption of a volcanic ash or lava flow.
• Drs. Giday WoldeGabriel and William Hart (Miami University in Oxford, OH)
produced a detailed chemical profile of the major constituents of the glass shards found in
volcanic ashes sandwiching the fossils. This unique chemical "fingerprint" allowed the
Ardipithecus-bearing layer to be tracked across a 9 kilometer arc of exposure, providing
an unparalleled transect across an ancient landscape.
ENVIRONMENTS AND HABITATS
What was Aramis like 4.4 million years ago?
• The radiometric dates for the Aramis site are almost unique because they show that the
fossils accumulated relatively rapidly. This meant that the researchers were able to
reconstruct a "snapshot" of the 4.4 Ma Ardipithecus environment with incredible
resolution.
• Various analyses were conducted to identify the species of plant, invertebrate animals,
birds, and small and large mammal fossils. Additionally, isotope signals of fossil soils
and enamel enabled the team to reconstruct the ecology and diet of many extinct
mammals, including Ardipithecus, as well as the overall environmental setting 4.4 million
years ago.
• These data show that the landscape was dominated by woodlands. There were fresh
water springs and small patches of fairly dense forest. There were palms at the forest
fringes, perhaps beside some small patches of open areas too. This wooded area graded
into wooded grasslands, perhaps many kilometers away.
• Other plants and animals associated with the "Ardi" fossils include: fig trees, hackberry
trees; land snails; diverse birds including owls, parrots and peafowl; small mammals like
shrews, mice and bats; porcupines, hyaenas, bears, pigs, rhinos, elephants, giraffes, two
kinds of monkeys, and several different kinds of antelopes.
ANATOMY
Why is the Ardipithecus ramidus partial skeleton so important?
• It preserves enough of the pelvis, leg, feet, arm, and hand to reconstruct how it walked
on the ground and how capable it was climbing in the trees.
• It is complete enough to estimate body weight and height.
• The details of body proportions can be compared with Australopithecus on the one
hand and modern apes on the other, thus elucidating the kind of ancestor we shared with
chimpanzees.
• The skull is complete enough to compare it with older fossils from Chad, and younger
Australopithecus from elsewhere in Africa.
• Because remains from many different Ardipithecus ramidus individuals were collected
from the same time horizon at Aramis, the position of "Ardi" within the overall species
distribution is discernable for many of her anatomical parts, giving a clear view of the
paleobiology of the species, rather than of a single individual.
How big was "Ardi" compared to "Lucy"?
• "Ardi" weighed about 50 Kgs, which is approximately 110 lbs. This is large for an
early hominid. Lucy only weighed about 25 Kgs--roughly half of "Ardi." However,
many bones other individuals in Lucy's species make it clear that she was one of its
smallest members, so Lucy should not be thought of being an average-sized
Australopithecus afarensis. Based on other bones recovered from Aramis, it is likely that
“Ardi” was a large female, and probably was larger than some males.
• As a female (see below), "Ardi's" large size indicates that males and females of
Ardipithecus ramidus did not differ a lot in body size (therefore different from gorillas in
which body size is highly sexually dimorphic).
How do you know "Ardi" was a female?
• In most primate species, males are larger and more robust than females. "Ardi's" skull
is small and lightly built, suggesting female.
• In most primate species, canine sexual dimorphism is very strong. Humans are an
exception, but even in humans, the canine is the most dimorphic tooth (male canines
average about 5% larger than in females). "Ardi's" upper and lower canines were both
among the smallest of the 21 Aramis canines found, again indicating that this individual
was female.
What do the Ardipithecus ramidus skull and teeth indicate?
• "Ardi" shares with Sahelanthropus (a 6+ Ma hominid cranium found in Chad) many
features of the brain case and face. One notable characteristic is the slightly forward
placement of the base of the skull (where the spinal chord comes out of the brain)
compared with apes, and also a probable downward facing back part of the skull (where
the neck muscles attach). These features are shared with Australopithecus and Homo and
indicate that both Ar. ramidus and Sahelanthropus were hominids.
• "Ardi's" cranial capacity was about 300-350 cc, slightly smaller than Australopithecus
and close to Sahelanthropus and chimpanzees (350-400 cc).
• The Ar. ramidus face was not as flat and massive as in later Australopithecus, but not
as projecting as modern apes, suggesting that the last common ancestor of humans and
apes might have had a face more like Ar. ramidus and Sahelanthropus, rather than that of
modern chimps or gorillas.
• The teeth of Ar. ramidus are fairly unspecialized (see below), so that it probably
resembled that of a Miocene ape ancestor, but with the important difference that it had
small male canines.
• Virtually all male primates except hominids have large projecting canines. In
chimpanzees and gorillas these teeth are tusk-like, and when they close down, the upper
canines are sharpened against the outer face of the lower third premolar. This action
"hones" the upper canine tooth to keep it sharpened as a weapon for threatening and
sometimes attacking other males. The males of Ardipithecus ramidus had small canines
that no longer functioned as weapons or displays in male-male, male-female, or
intergroup conflicts.
What do the bones of the Ardipithecus ramidus body indicate?
• Ardipithecus was both arboreal and terrestrial. "Ardi" had a mixture of: 1) primitive ape
or monkey-like features showing that it was capable of efficient climbing in trees, and, 2)
evolved Australopithecus-like features for two-legged walking on the ground.
• Ardipithecus had a mosaic anatomy of the pelvis. The broad upper part enabled it to
walk on two legs with a straightened hip (as with Australopithecus and humans), and the
long lower part of the pelvis indicates retention of powerful hamstring muscles for
climbing.
• It retained a fully opposable grasping big toe, which also means that it didn't have the
arch-like foot structure of Australopithecus and humans.
• The remainder of the foot was not as flexible as are those of modern great apes, and
was useful for pushing-off and for arboreal clambering, but not as useful in climbing up
and down tree trunks and vines as are the feet of living chimpanzees.
• Limb proportions of Ardipithecus were, surprisingly, not like chimps or gorillas (which
have very long arms and short legs). "Ardi's" proportions were like those of primitive
extinct apes, or even monkeys.
• The Ardipithecus hand was also not chimp- or gorilla-like, but more like those of
earlier extinct apes. Chimpanzee hands (and gorilla hands to a certain degree) have
elongate palms and a series of special joint and ligament structures that enable chimps to
suspend their body from a grasp above their heads. This is necessary for both frequent
climbing up and down trees, and for securing themselves high in the trees. These
adaptations also enable chimps and young gorillas to literally hang and swing in the trees.
On the ground, they walk on their backs of their middle digits, which we call knucklewalking. Chimpanzee and gorilla wrists and palms show highly evolved structures that
evince this unusual knuckle-walking locomotion.
• The Ardipithecus ramidus hand shows none of these specializations seen in the hands
of living apes. Instead, the fossils show that Ardipithecus retained the more primitive
extinct ape style of palm-walking. Moreover, Ardipithecus had an extremely flexible
mid-portion of the hand that allowed it to hold on to branches in different grasping
positions.
• Ardipithecus ramidus did not knuckle-walk, nor are there any signs that any of its
ancestors ever did.
LOCOMOTION
How did Ardipithecus ramidus move?
• On the ground it walked bipedally on its two hind legs, but because it still had a fully
opposable grasping big toe and did not have an arched foot, it walked flat-footed and
pushed off using the outside portion of its foot.
• This also meant that Ardipithecus could not walk or run effectively for long distances
as humans can.
• When in trees, Ardipithecus would have been a slower, more careful climber than are
chimpanzees. For example, chimpanzees are so agile (even though they are very large)
that they can cooperate to chase, trap, and kill red colobus monkeys, which are even more
agile than they are. But even with cooperation, it is unlikely that "Ardi's" species could
have performed those kinds of feats.
• "Ardi's" hands and back were much more flexible than are those of chimpanzees. This
meant that she could twist herself into many different postures when on top of large tree
limbs or in a network of branches. This may have helped her feed, nest, and care for her
young in the trees.
• On the ground, her hands were much more effective than those of chimpanzees for
manipulating her environment to get underground foods, to capture small prey, and to
carry things.
Did Ardipithecus use tools?
• Probably. Modern chimpanzees occasionally use crude tools, and so do New World
Capuchin monkeys and even a few birds. So "Ardi" probably did. However, there is no
evidence for stone tool making for almost another two million years (the first evidence
for stone tool making is at 2.6 Ma, from the nearby Gona site, also in Ethiopia)
DIET
What did Ardipithecus ramidus eat?
• Ardipithecus teeth were an all-purpose type, with low rounded molar cusps. Chimps
have specialized molars with thin enamel, good for crushing juicy fruits and also for
shredding leaves. Gorillas have very high cusps, good for cutting and folding up fibrous
leaves, stems and bark. Based on the shape of the teeth, the Ardipithecus diet differed
from any living African ape.
• Ardipithecus molar teeth were much smaller than those of the more open-land feeding
Australopithecus. Australopithecus molars also had thicker enamel, so that they were
much more durable to heavy chewing of hard and tough foods with adhering grit.
• As with almost all large bodied primates, "Ardi" was probably omnivorous, including
fruit, when she could procure it. But members of the species probably spent considerable
time in the woodland searching for hard-to-find nutritious plants, mushrooms,
invertebrates, maybe even some small vertebrates.
BEHAVIOR
Hypothesizing the social behavior of Ardipithecus
• One of the most important things that Ardipithecus reveals is the evolutionary history
of the canine complex in human evolution. A detailed analysis of the Ardipithecus
ramidus canine and premolars, and comparisons with the few available even-older
hominid canines, show that canine reduction was already well-advanced even by 6
million years ago. Typically in apes and monkeys with big canines, the upper jaw's
canines are used as weapons. By 4.4 Ma, Ar. ramidus canine function had changed
fundamentally. Their reduced upper canines were not projecting as in apes. Nor did
these canines sharpen against the lower third premolar; they were diamond-shaped and
blunt, rather than V-shaped in side view.
• So Ardipithecus probably had social structure unlike that of any living primate--one in
which multiple males and multiple females lived together, but without strong male-male
conflicts. Males were probably pair-bonded to specific females, and may have aided
females by gathering rare and valuable foods that they would regularly share with them.
• These changes in behavior may be related to why bipedality happened in the first place.
Carrying is very difficult in woodlands without the forelimbs being free. And such
"provisioning" by males would have allowed females to intensify their parenting, and to
cooperate more with other females.
• Integrating the new fossil evidence with other independent data drawn from a wide
range of biological sciences, Professor Owen Lovejoy of Kent State University outlines
an "adaptive suite" for Ardipithecus and its implications for the evolution of early
hominid anatomy and behavior in one of the 11 papers published in Science.
SOME ADDITIONAL IMPLICATIONS
What are the implications for the evolution of living great apes and the last common
ancestor that chimpanzees and humans shared?
• The timing of divergence between lines leading to chimps and hominids has been
suggested to lie anywhere between 5 and 10 million years ago. Ardipithecus ramidus is
obviously too geologically young to be that common ancestor.
• However, Ardipithecus ramidus important because it is the closest we have ever come
to this still-unfound "last common ancestor" that hominids and chimpanzees once shared.
Armed with the new Ardipithecus fossils, we can now better infer what that creature was
like.
• Ardipithecus ramidus exhibits a much more primitive anatomy all through its body and
head than seen in Australopithecus. It is very probable that in most (if not all) important
ways, Ardipithecus ramidus represents the general adaptation of even earlier hominids,
now extending back to at least 6 million years ago.
• Ardipithecus ramidus suggests that after the last common ancestor we shared with
chimpanzees and gorillas, the body structures of these apes became specialized (evolved)
in peculiar ways. The combination of large body size and climbing underlies these
adaptations of living apes: the arms and palms elongated, the back became stiffer, and
the wrists and palms evolved protections from damage while supporting their large body
mass. This also led to knuckle-walking when on the ground.
• Another implication is that the upright body postures of humans and modern apes were
acquired independently. Extreme upright body posture evolved in apes because of
frequent vertical climbing and suspension, and in humans because of bipedality.
Understanding one of our closest relatives, the chimpanzee.
• Ardipithecus gives clues as to how chimpanzees might have evolved from the last
common ancestor. Ardipithecus shows that throughout the body--from head and teeth, to
torso, hands, and feet--chimps have some very highly evolved, specialized features.
Many of these features appear to be linked to a dietary preference for ripe fruits.
• Chimps have exceptionally large incisors and a projecting mouth particularly suitable
for eating fruits. Their molars are also specialized to combine crushing and shredding.
They have specialized backs, limbs, hands, and feet, and are adapted to both terrestrial
movement on the forest floors (and between forest patches) via knuckle-walking, and to
climbing high into the trees and hanging from branches when necessary. All this can be
seen as probably related to chimpanzees specializing on ripe fruits as a main food item,
and having to cope with patchy and dispersed distributions of their preferred fruits.
• Chimpanzee social system and behavior may also be linked with this. Chimps have
canines that are probably secondarily enlarged, and their faces are very projecting, also a
unique elaboration. So, the chimpanzee's aggressive social behavior is, in part, highly
specialized, and was probably not shared by the last common ancestor of hominids and
chimpanzees.
What are the implications for later hominids (Australopithecus)?
• There are several alternative hypotheses about evolutionary relationships described and
illustrated in the lead (summary) paper in Science. Australopithecus may have evolved
directly and rapidly from Ardipithecus ramidus between 4.4 and 4.1 million years ago.
Another possibility is that Ardipithecus ramidus was a relict species that may have
persisted alongside its descendant Australopithecus.
• Testing these hypotheses will require additional fossils from other sites. So far,
however, Ardipithecus has always been found in older strata than Australopithecus, and
the two have not yet been found at the same time horizon.
• Ardipithecus shows that hominids became fundamentally terrestrial only at the
Australopithecus stage of evolution. Australopithecus had forfeited much of its climbing
ability (they were almost as bad at climbing in trees as are humans), and were probably
the first hominids to range extensively into more open habitats. Their skulls and teeth
indicate that their broader niche included more hard/tough and abrasive savanna foods
(hard fruits, seeds/nuts, abrasive roots and corms, so on). Scavenging and capturing
small mammals for meat might also have started with Australopithecus, paving the way
to the evolution and geographic expansion of Homo, including later elaboration of
technology and expansion of the brain.
THE FAMILY TREE
Is Ardipithecus the fossil "Missing Link?"
• The concept of a "missing link" was long ago abandoned in science for several reasons.
There NEVER WAS a link between living forms. We did NOT evolve from living
monkeys or apes. Darwin correctly conceived evolution as a branching tree of life, on
which living species were the growing and sometimes dividing twigs on ever-spreading
branches.
• All discovered fossils represent only a very minute fraction of the species that they
represent. So depicting any individual fossil as a "special link" is absurd. The fossils we
find simply allow inferences about the extinct species to which they belonged; the more
and the better preserved the fossils, the better the inferences about the paleobiology of the
species they represent.
• The Ardipithecus fossils are one of three known hominid genera. Genus Homo is the
one we are in. Australopithecus is the one that "Lucy was in." These genera each
represent stages of our evolution. Ardipithecus now becomes the earliest known stage on
our family branch of the primate evolutionary tree.
Is the "Ardi" skeleton a human ancestor?
If she didn't have offspring, as an individual, she could not have been a human ancestor,
because her specific DNA would not have been passed on. We cannot tell whether she
had children or not.
Is the species Ardipithecus ramidus our direct ancestor?
We cannot tell that yet, because we do not have enough fossils from different places and
time periods. We will need many more fossil recoveries from the period of 3-5 million
years ago to confidently answer that question in the future. But if Ardipithecus ramidus
was not actually the species directly ancestral to us, she must have been closely related to
it, and would have been similar in appearance and adaptation.
Is the genus Ardipithecus our ancestor?
There is no evidence available to refute the hypothesis that a species of Ardipithecus was
the ancestor of Australopithecus, (or, indeed, that some species of Australopithecus was
the ancestor of Homo). These genera can be thought of as three, mostly successive
"adaptive zones" or "plateaus" or "phases" that hominid species occupied during their
evolution.
WHY DOES ANY OF THIS MATTER?
• We can now discern in much greater detail the basic steps in our evolution from ancient
apes. The details of our evolutionary past increasingly show the complex
interrelationship of environmental change, habitat transformation, and biological
adaptation.
• All indications are that our biological and social roots are evolutionarily deep.
• Ardipithecus bridges the early gap between Australopithecus and more ancient apes,
and shows that chimpanzees, bonobos, and gorillas have each been evolving on their own
unique evolutionary pathways while we hominids have taken different evolutionary
trajectories.
• Ardipithecus connects us with the rest of life's tree in ways that living apes cannot.
• Living apes and modern genetics provide valuable windows on human evolution, but
the Ardipithecus discoveries demonstrate the unique power of the fossil record to reveal
the vanished worlds of our ancient African past.
THE MIDDLE AWASH RECORD
• The Ethiopian Afar Region has yielded the longest record of human evolution on planet
Earth, now with hominid fossils sampled across six million years.
http://middleawash.berkeley.edu
• The Middle Awash project has been active since 1981 and has published ~170 books,
monographs, and journal articles, totaling ~6,600 printed pages.
• The Middle Awash study area has the longest, most continuous record of human
evolution anywhere on earth. Here, a total of ~300 total hominid specimens are known
from 14 separate superimposed stratigraphic horizons sampling the last six million years.
Thousands of stone tools and animal fossils have been recovered. All these antiquities
are national treasures of global significance, permanently curated at the National Museum
of Ethiopia as world heritage. They provide strong evidence for biological and
technological evolution.
• The Middle Awash team’s previous hominid discoveries include (youngest to oldest):
• Homo sapiens sapiens: an approximately 80,000 year-old anatomically modern
human cranial vault with Middle Stone Age tools was found at Aduma.
(AJPA 2004)
• Homo sapiens idaltu: three crania from Herto established that anatomically nearmodern humans lived here 160,000 years ago.
(Nature 2003)
• Homo erectus: a calvaria and three thighbones of Homo erectus dated to 1 million
years ago were found with Acheulean stone tools at Bouri Daka
(Nature 2002)
• Australopithecus garhi: a 2.5 million-year-old species of Australopithecus was
found in the same strata with evidence of early stone tool making and butchery of
large animals at Bouri Hata.
(Science 1999)
• Australopithecus afarensis: 3.4 million-year-old teeth, jaws and limb bones from
the "Lucy" species were found at Maka.
(Nature 1984, 1993)
• Au. anamensis: 4.0-4.2 million-year-old teeth, jaws and limb bones from the
earliest known Australopithecus species, found at Asa Issie. Also found at Aramis,
but only in layers 80 meters above Ar. ramidus.
(Nature 2006)
• Ardipithecus ramidus: a 4.4 million-year-old species was named on the basis of a
small sample of fragments in 1994. A massive research effort at the site followed
this and the recovery of a partial skeleton, culminating with the current set of
publications.
(Nature 1994; Science, 2009)
• Ardipithecus kadabba: a 5.7 million-year-old hominid that is similar to those found
in Chad and Kenya from similar time horizons, found on the western escarpment
of the Middle Awash.
(Nature 2001; Science 2004)
THE MIDDLE AWASH PROJECT
• The Middle Awash research team includes over 70 scientists from 19 different
countries, specializing in geology, archaeology, paleontology, and evolutionary biology.
• The Middle Awash project operates under a permit from the Ethiopian Authority for
Research and Conservation of Cultural Heritage of the Ethiopian Ministry of Culture and
Tourism. The team conducts field research each autumn.
• The discovery of these fossils over several different field seasons was a result of
careful scheduling by the Middle Awash project to revisit and resurvey rich fossil
localities. Each locality in the study area is monitored for possible freshly eroded fossils
to "harvest" after a given time interval. Erosional conditions in this region insure the
success of such site re-visitation. The Aramis discoveries witness the effectiveness of
such site management.
• The Middle Awash research project was initiated in 1981 by the late J. Desmond Clark.
See tributes at http://middleawash.berkeley.edu
• All fossils found in Ethiopia are prepared, studied, and permanently curated at the
National Museum of Ethiopia where important new museum facilities will soon open.
• For more details see the project website: http://middleawash.berkeley.edu
WHAT'S NEXT
• Books in a series published by the University of California Press are currently
published (2008, 2009), or in preparation or production.
• The project continues its normal annual cycle of ongoing autumn fieldwork and yeararound laboratory work in Addis Ababa and around the world.
SUPPORT
• The international field research effort in the Middle Awash is supported by grants from
the U.S. National Science Foundation (Physical Anthropology Program) and the Institute
of Geophysics and Planetary Physics of the University of California at Los Alamos
National Laboratory.
• Additional research contributions were made by the Hampton Fund for International
Initiatives at Miami University, by the Japan Society for the Promotion of Science, and
by the NSF HOMINID program (Revealing Hominid Origins Initiative).
• Generous seed funding for the documentary was provided by The Fernbank Museum of
Natural History, Atlanta [Susan Neugent President & CEO; Jesse Crawford, former
Chairman of the Board (in 1999)]. fernbankmuseum.org
• See additional acknowledgements at the end of the published papers.
OTHER RESOURCES
http://middleawash.berkeley.edu
http://rhoi.berkeley.edu/
http://www.discovery.com/ardi