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Press Backgrounder: "Ardipithecus"
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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 “ape-man” Australopithecus, until now the most completely known early hominid genus thanks to fossils like the partial 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-VP-6/500 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 kilometer 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.
- 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.
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 meters 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, Ohio) 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 pants 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.
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 of 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 knuckle-walking. 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.
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)
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.
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 is 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.
Project co-Director and geologist, Dr. Giday WoldeGabriel, Los Alamos National Laboratory:
"These are the results of a mission to our deep African past."
Project geochronologist, Professor Paul Renne, Berkeley Geochronology Center:
"Because they were sandwiched between two volcanic horizons with virtually indistinguishable dates, the thousands of fossils collected at Aramis are among the best calibrated in the world, at 4.4 million years ago."
Project co-Director and paleoanthropologist, Dr. Berhane Asfaw, Rift Valley Research Service, Addis Ababa:
"The skull of Ardipithecus is the smallest of any fossil hominid, and really helps us understand what came before "Ardi," and how later hominids evolved."
Project member and Curator/paleontologist, Yohannes Haile-Selassie, Cleveland Museum of Natural History:
"Ardipithecus ramidus and its prevailing anatomy revolutionize the way most of us understood the earlier part of our evolutionary history."
Project anatomist and evolutionary biologist, Professor C. Owen Lovejoy, Kent State University:
"The novel anatomy that we describe in these papers fundamentally alters our understanding of human origins and early evolution."
Project co-Director and paleontologist, Prof. Tim White, Human Evolution Research Center, UC Berkeley:
"This is not an ordinary fossil. It's not a chimp. It's not a human. It shows us what we used to be."
Project paleoanthropologist, Dr. Gen Suwa, the University of Tokyo:
“With such a complete skeleton, and with so many other individuals of the same species at the same time horizon, we can really understand the biology of this hominid."
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.
Homo sapiens idaltu: three crania from Herto established that anatomically near-modern humans lived here 160,000 years ago.
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
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.
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.
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)
- Homo sapiens sapiens: an approximately 80,000 year-old anatomically modern human cranial vault with Middle Stone Age tools was found at Aduma.
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
- 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 year-around laboratory work in Addis Ababa and around the world.
- 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.
FURTHER INFORMATION AND CONTACTS
The 47 co-authors on the 11 scientific papers are specialists across a wide range of disciplines, and their contact information is available in the Science special issue. All are available for comment. Key personnel include:
- Dr. Berhane Asfaw and Dr. Yonas Beyene reside in Addis Ababa (7 hours ahead of EST) and will coordinate all Ethiopian-related public information with the Ministry of Culture and Tourism, including the only press conference on the discovery, to be held in Addis Ababa upon embargo lift. Telephones: 251-911-22-31-94 (BA); E-mail: <email@example.com> 251-911-21-68-93 (YB); E-mail: <firstname.lastname@example.org>.
- Professor Tim White directs the Human Evolution Research Center (HERC.berkeley.edu) and teaches in the Department of Integrative Biology at U.C. Berkeley. E-mail: <email@example.com>; tel. 510-642-2889 (no message machine).
- Professor Owen Lovejoy is a University Professor at Kent State University, Ohio, and is an expert in hominid paleobiology. E-mail: <firstname.lastname@example.org>; tel. 330-672-GENE.
- Professor Elisabeth Vrba is a paleontologist at Yale University (Department of Geology and Geophysics) and specializes in fossil antelopes, environment, and evolutionary biology. E-mail: <email@example.com>; tel. 203-432-5008.
- Dr. Giday WoldeGabriel is at Los Alamos National Laboratory. E-mail: <firstname.lastname@example.org>; tel. 505-667-8749.
- Professor Leslea Hlusko is a biologist at the University of California, Berkeley, and specializes in genetics and fossil monkeys. E-mail: <email@example.com>; tel. 510-643-8838.
- Professor Stan Ambrose is a Professor of Anthropology at the University of Illinois, and performed all isotopic analyses. E-mail: <firstname.lastname@example.org>; tel. 217-244-3504.
- Dr. Paul Renne the Director of the Berkeley Geochronology Center and an adjunct professor in the Department of Earth and Planetary Science at U.C. Berkeley. E-mail: <email@example.com>; tel. 510-644-1350 (9200).
- Professor Bill Hart chairs the Department of Geology at Miami University, Ohio. E-mail: <firstname.lastname@example.org>; tel. 513-529-3216.
- Professor Gen Suwa is a paleoanthropologist at the University Museum at the University of Tokyo, Japan. E-mail: <email@example.com>.
- Project-released field videotape segments and photographs are available from AAAS.
- Still photographs documenting these discoveries (including field and laboratory shots of specimens and scientists), as well as artwork by Jay H. Matternes are available via AAAS to journalists preparing breaking news coverage that will publish or broadcast before October 15, 2PM. Additional photos can be purchased through David L. Brill Photography, 552 Hwy. 279, Fayetteville, GA 30214, USA: Phone/Fax: 770-461-5488. E-mail: <firstname.lastname@example.org>. His special website with visuals has been established to help journalists and editors choose images to illustrate the story. Additional artwork can be purchased through J. H. Matternes, http://www.jay-matternes.com/
1 October 2009