Ardi displaces Lucy as oldest hominid skeleton

By | October 3, 2009

skeletonhumanoidNearly 17 years after plucking the fossilized tooth of a new human ancestor from a pebbly desert in Ethiopia, an international team of scientists today (Thursday, Oct. 1) announced their reconstruction of a partial skeleton of the hominid, Ardipithecus ramidus, which they say revolutionizes our understanding of the earliest phase of human evolution.

The female skeleton, nicknamed Ardi, is 4.4 million years old, 1.2 million years older than the skeleton of Lucy, or Australopithecus afarensis, the most famous and, until now, the earliest hominid skeleton ever found. Hominids are all fossil species closer to modern humans than to chimps and bonobos, which are our closest living relatives.

“This is the oldest hominid skeleton on Earth,” said Tim White, University of California, Berkeley, professor of integrative biology and one of the co-directors of the Middle Awash Project, a team of 70 scientists that reconstructed the skeleton and other fossils found with it. “This is the most detailed snapshot we have of one of the earliest hominids and of what Africa was like 4.4 million years ago.”

White and the team will publish the results of their analysis in 11 papers in the Oct. 2 issue of the journal Science, which has Ardi on the cover. They announced their findings at press conferences held simultaneously today in Washington, D.C., and Addis Ababa, Ethiopia.

The team’s reconstruction of the 4-foot-tall skeleton and of Ardi’s environment – a woodland replete with parrots, monkeys, bears, rhinos, elephants and antelope – alters the picture scientists have had of the first hominid to arise after the hominid line that would eventually lead to humans split about 6 million years ago from the line that led to living chimpanzees.

Based on a thorough analysis of the creature’s foot, leg and pelvis bones, for example, the scientists concluded that Ardi was bipedal – she walked on two legs – despite being flat-footed and likely unable to walk or run for long distances.

In part, this primitive ability to walk upright is because Ardi was still a tree-dweller, they said. She had an opposable big toe, like chimpanzees, but was probably not as agile in the trees as a chimp. Unlike chimps, however, she could have carried things while walking upright on the ground, and would have been able to manipulate objects better than a chimp. And, contrary to what many scientists have thought, Ardi did not walk on her knuckles, White said.

“Ardi was not a chimpanzee, but she wasn’t human,” stressed White, who directs UC Berkeley’s Human Evolution Research Center. “When climbing on all fours, she did not walk on her knuckles, like a chimp or gorilla, but on her palms. No ape today walks on its palms.”

Ardi’s successor, Lucy, was much better adapted for walking on the ground, suggesting that “hominids became fundamentally terrestrial only at the Australopithecus stage of evolution,” he said.

Based on Ardi’s small, blunt, upper canine teeth, the team also argues that the males of that species did not engage in the same fearsome, teeth-baring threat behavior common in chimpanzees, gorillas and orangutans. Instead, they must have had a more amicable relationship, the scientists said, implying that several pair-bonded couples lived together in social units. Males may even have helped in gathering food for sharing.

“The novel anatomy that we describe in these papers fundamentally alters our understanding of human origins and early evolution,” said anatomist and evolutionary biologist C. Owen Lovejoy of Kent State University, a scientist with the project. In a summary article in Science, Lovejoy wrote that these and other behaviors “would have substantially intensified male parental investment – a breakthrough adaptation with anatomical, behavioral, and physiological consequences for early hominids and for all of their descendants, including ourselves.”

Until now, the oldest fossil skeleton of a human ancestor was the 3.2-million-year-old partial skeleton of Lucy, discovered in the Afar depression of Ethiopia, near Hadar, in 1974 and named Au. afarensis.

In 1992, however, while surveying a site elsewhere in the Afar, near the village of Aramis, 140 miles northeast of Addis Ababa, Middle Awash Project scientist Gen Suwa discovered a tooth from a more primitive creature more than 1 million years older than Lucy. After more fossils of the creature were found in the area from some 17 individuals, Suwa, White and project co-leader Berhane Asfaw published the discovery in the journal Nature in 1994.

mapAlthough that first paper initially conservatively placed the chimp-like creature in the Australopithecus genus with Lucy, the team subsequently created a new genus – Ardipithecus – for the hominid because of the fossils’ significantly more primitive features.

A digital representation of Ardi's skullA digitally rendered composite image of Ardi's hand After preparing their first report, the scientists continued to find more Ar. ramidus fossils in the Aramis area. A hand-bone discovered in 1994 by project scientist Yohannes Haile-Selassie, a paleontologist and curator at the Cleveland Museum of Natural History, eventually led the team to the partial skeleton now known as Ardi, which they excavated during three subsequent field seasons. The skeleton was disarticulated and scattered, and broken into smaller pieces: 125 fragments of skulls, teeth, arms, hands, the pelvis, legs and feet. In addition to this skeleton, the area yielded a total of 110 other catalogued specimens representing body parts of at least 36 other Ardipithecus individuals.

After the bones were excavated at the site, they were molded and painstakingly removed from their protective plaster jackets in the laboratory in Addis Ababa, where they were then photographed and reconstructed. Micro-CT scanners were used to study the inner and outer anatomy of the bones and teeth, and scanning electron microscopes were used to study the structure and surface details. The 5,000 micro-CT slices through the broken skull allowed the team to reconstruct it on a computer and then “print” it on a 3-D stereolithic printer at the University of Tokyo. A cast of Ardi’s skull, along with video and comparisons, can be seen now in the Human Evolution display on the second floor of UC Berkeley’s Valley Life Sciences Building.

In all, 47 scientists from 10 countries contributed to the 11 Science papers, providing detailed analyses of the feet, pelvis, teeth and general anatomy of Ar. ramidus and reconstructions of the geology and biology of the area where Ardi lived 4.4 million years ago. Two of the papers analyze more than 150,000 plant and animal fossils – including 6,000 individually catalogued vertebrate fossils – to reconstruct the large and small mammals and birds of the area. Among these are 20 species new to science, including shrews, bats, rodents, hares and carnivores.

“We had to do a lot of work to bring this world back to life, but by merging the skeletal information with the data on biology and geology, we end up with a very, very high-resolution snapshot of Ardi’s world,” White said. “It was a very cold case investigation.”

CTs of the tooth enamel, for example, revealed that Ardi was an omnivore, eating a diet different from that of living African apes, such as chimps, which eat primarily fruit, and gorillas, which eat primarily leaves, stems and bark. The team suggests that Ardipithecus spent a lot of time on the ground looking for nutritious plants, mushrooms, invertebrates and perhaps small vertebrates.

It wasn’t until 1 million years after Ardi that hominids like Lucy were able to range extensively into the savannas and develop the robust premolar and molar teeth with thick enamel needed to eat hard seeds and roots. One of these species then started scavenging and using stone tools to butcher larger mammals for meat, “paving the way to the evolution and geographic expansion of Homo, including later elaboration of technology and expansion of the brain,” White said.

White said Ardi, who probably weighed about 110 pounds, had a brain close to the size of today’s chimpanzees – one-fifth that of Homo sapiens – and a small face. Males and females were about the same size. The hominid’s lack of resemblance to either chimp or modern humans indicates that the last common ancestor of apes and humans looked like neither, he said, and that both lines have evolved significantly since they split 6 million years ago.

White admits that the relationship between Ar. ramidus and the Australopithecus fossils the team has found about 80 meters higher in the strata of the Ethiopian desert is tentative. Nevertheless, he said Ardi’s species could be the direct ancestor of Lucy’s species, which could be the direct ancestor of modern humans. Without additional fossil evidence, however, connecting the individual or species dots is hazardous, White said.

Ardipithecus ramidus is only known from this one productive site in Ethiopia,” White said. “We hope others will find more fossils, in particular fossils from the period of 3-5 million years ago, to test this hypothesis of descent.”

via Ardi displaces Lucy as oldest hominid skeleton.

16 thoughts on “Ardi displaces Lucy as oldest hominid skeleton

  1. Pingback: links for 2009-10-03 « Fantasising Zombies

  2. Cole

    You know what I think is ridiculous? The fact that South Africa, a second world country with many people without food or shelter, spent a ton of money on a museum of evolution. That’s money that could have been used to help all these people, and it was used to build a museum honoring an idea that hasn’t even been proven! How stupid can some people be?

    1. Xeno Post author

      Poverty is often inversely related to education. Also some countries survive on mostly tourism, so I think that long term this museum may help South Africa. Bring in people from all over the world with money and you will help the about 30 million people living below the poverty line in this nation which may be the birthplace of us all. I’d like to see the museum of evolution.

      People visit churches around the globe to honor faith based views. Faith, by definition, is a firm belief in something for which there is no proof. Why do people who choose to belong to a “no proof” group complain about proof?

      Science is not a vast conspiracy of people who hate Christians and are therefore plotting to subvert the truth of the bible. If the observable facts supported the biblical interpretation it would be taught rather than evolution… but that is not the case. Instead the fossil and genetic evidence shows that evolution best explains life on earth as it is today.

      More than a “theory” evolution is an observed fact, like gravity. Yes, there is physical evidence for evolution. We’ve seen the process happen. We know it happens.

      Are we humans the result of the same evolutionary process? Seems likely.

      1. Cole

        I know science isn’t just a group who hate Christians. I’m a Christian and I love science. I was ready to counter for the “observed fact” remark. Have we ever observed one species evolve into another. We have witnessed micro-evolution, the adaption of species to better survive in an environment, but never macro-evolution. We only see what we believe to be remnants of what we think happened, but, as it would have happened in the past, there is no indisputable proof of evolution.

        1. Xeno Post author

          Hello,
          We can observe a second, a week, or a month, or a year… but neither of us can observe 1,000 years, or a million years, or a billion years. Prove to me that 1,000 years exists. You can’t. 😉

          Yes, we have observed one species evolve into another. Micro-evolution is macro-evolution. The only difference is the time scale. A cat will not become a bird, but birds and cats had a common ancestor, a long time ago. We can see this by looking at their shared genetics and at the fossil record. Fossils of transitional species are observable physical evidence showing how current species on earth came to be.

          If you want to get creative, there is actually no “indisputable proof” for anything. No one can prove that the entire Universe is not a dream by a brain in a vat.

        2. Cole

          I wish this site would allow for more replies to a single comment. Anyways, I don’t want to go there. I look forward to future posts.

        3. Xeno Post author

          Agreed, it makes the conversations more difficult to follow.

          The brain in the vat dreamed that you would not want to go there and that I would write this about you not wanting to go there and that thousands of people would read this. We all have once again done exactly what the brain dreamed we did. I can not prove that God is not a brain that dreams us.

  3. bluefly

    You can’t even prove there is a God. At least with science we do have physical evidence. Any religion is classified as an occult. A group of people who believe in whatever they are worshiping. But you can’t deny the physical proof of evolution. With genome typing and other forms of DNA we are proving our theories. I agree with xeno.

  4. Ajeetkunedodude

    Ardi???
    Come ooon we all know that evolution of the biological is a joke.
    It is a shame for us real scientists to witness such distortion of truth.
    An Ape is all Ardi is with opposing toes ardi could not walk far at all.
    Perfect for tree climbing though.
    The bones would crumble they were in such poor condition thus taking years of manipulating by EVOLUTIONISTS.
    Then we have the typical short legs long arms.
    The face is guess work also.
    Hairy body etc.
    What is this nonsense a Vagina?
    Where in the hell did that come from?
    This is just another deception to fit a presupposition.

    Who said there was no physical evidence for proof of God?
    WE are the evidence you fool.
    Have you never researched the chance of one earth species alone forming from chemical formula?
    The chances scientifically speaking are zero.
    You lot have been brain washed.
    You lot support a lie that confirms your lie which you have been lied into believeing.

    Evolution theory is DEAD.
    Research cambrian explosion, Chances of life from the Bang, Speed of light slowing and stoping then being froze etc etc.

    1. Xeno Post author

      Come ooon, we all know that denying evolution is a joke.
      It is a shame for us real scientists to witness such distortion of truth.
      Apes did not have opposing toes.
      If things that would crumple are not allowed as evidence, then we need to throw out some very old scrolls upon which things biblical in nature are written.
      Hamsters have short arms too, so Ardi must be a hamster.
      Reconstruction of faces from bone fragments is somewhat of an art, but they’ve been at it for years.
      Cats have hairy bodies, so Ardi must be a cat.
      Where did vaginas come from? They evolved, man. Anatomists can tell gender from things like teeth and bone fragments due to the vast number of samples available.
      Your presupposition that evolution is false ignores the physical evidence.

      We are evidence of evolution, my friend.
      You are correct, the chance of anything evolving from a chemical formula is ZERO.
      But things do evolve from chemicals. With the building blocks of life spread throughout the universe and with physical laws that govern local interactions of atoms, the rise of self replicating systems is inevitable.

      Evolution is an observed fact, very much alive and very real.
      Research cambrian explosion, panspermia, and … what are you talking about with regard to light? Yes, of course it can slow and stop and even be frozen. What does that have to do with evolution?

      1. Cole

        Regardless of who is correct, it is futile to argue on a topic such as this because both sides in this worldwide debate never give up, no matter how much scrutiny they are faced with. It is human nature to hang on to things you believe in, and have believed in, and to want to discover the unknown.

        As we’ve seen from the past, people tend to fill in what can’t or has not been discovered with their own ideas, which is how some religions formed, along with other scientific beliefs such as geocentricity.

        This blog is for the discussion of strange and interesting things, don’t smother it in arguments.

      2. Xeno Post author

        I think of it as healthy debate.

        I don’t know if you believe this, but I know in my heart of hearts that I would change my views about creation and evolution *right now* if someone had evidence beyond name calling, dogma, faulty logic and old stories.

        It would be really great news to learn that there is a creator after all! This is why I listen carefully to people and examine each point they make. I’d like to be convinced … but all of the evidence and arguments I’ve examined show no proof for the one and a lot of proof for the other.

        I feel our creation, how humans came to be, is one of the strangest and most interesting things about this planet.

      3. Xeno Post author

        I don’t think of it as a difficult road. I relish the hunt for the truth. I really enjoy finding out when I’m wrong about something and updating my views.

      4. Cole

        True. And sometimes even views on views can change.

        Atheism can easily be defined as religion. There are many ways to define religion, but this one sums up every possibility: “A religion is a system of human thought which usually includes a set of narratives, symbols, beliefs and practices that give meaning to the practitioner’s experiences of life through reference to a higher power, deity or deities, or ultimate truth.” Ultimate truth, there’s the keyword. An ultimate truth is a truth that applies to all existence. So, if there’s no deity or supreme being, then obviously that applies everywhere. So, atheism is, by definition, a religion.

        However, definitions are not always absolute. What you said earlier about faith being defined as a firm belief in something for which there is no proof is a prime example. Obviously, if this was how Christians, or any other religion for that matter, defined this, why would they believe it. Religions obviously believe they have proof of their beliefs, and yet they still call it faith. Therefore, faith has multiple definitions. And obviously, atheists don’t define themselves as a religion.

        The question is, how can a universal definition be written for these things? Perhaps the most-common usage? In which case, faith would be defined in a religious sense, because that is how most people use it, and not the technical definition we have now, that you provided. Also, if defined by most-common usage, atheism would not be considered a religion. And yet, ultimately it is, because it still must maintain the original religion definition I mentioned earlier, because it is impossible for there to be a single definition for anything, at all. By the same logic, faith could not maintain it’s religious meaning without also maintaining it’s technical definition. No one definition can exist, because as long as one person calls uses any word in a way it is not normally used, it becomes a valid definition. By this reasoning, I could easily pick up my “cellphone” and start clipping my toenails.

        So, atheism both is and isn’t a religion, just as faith both is and isn’t as you defined it. The only problem with atheism being a religion is that I’m not sure if I want to be writing it with a capital “A.”;)

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