• Was there a fork in our family tree?

    msnbc.com

    How did pre-humans like australopiths, shown at left in this illustration, make the transition to early members of the genus Homo, shown at right? Perhaps it happened more than once.

    By Alan Boyle, Science Editor, NBC News

    The discoverer of the famous "Lucy" fossil says fresh findings suggest that more than one ancient species made the transition to more humanlike forms in different parts of Africa.

    Arizona State University paleoanthropologist Don Johanson shook up the scientific world in 1974 when he came across the traces of a 3.2 million-year-old skeleton in Ethiopia, a pre-human ancestor that came to be called Lucy. A similar shake-up may well be in the works due to the detailed analysis of another set of 1.977 million-year-old bones found in South Africa.

    In a series of studies published this week in the journal Science, researchers make a strong case that the bones, ascribed to a species called Australopithecus sediba, illustrate how the bodies of humanlike primates became more suited for upright walking, tool-making — and bigger brains.

    The international research team, led by the University of Witwatersrand's Lee Berger, says A. sediba is a good representative of the type of creature leading to the emergence of the genus Homo, which includes us Homo sapiens types as well as Neanderthals and a host of other now-extinct species.

    Courtesy of Donald Johanson

    Anthropologist Don Johanson holds a cast of the skull of Lucy, one of the world's best-known hominid fossils.

    But Johanson told me today that few of the reports about the latest findings touch on "the real crux of the matter." Even though A. sediba is a transitional form, with features of Australopithecus as well as Homo, he said there are other specimens of the genus Homo in eastern Africa that have been dated to roughly the same time. "There is a diversity of Homo already at 1.8 million years," he said.

    In fact, at least one of the fossil bones traditionally ascribed to Homo — an upper jaw from the same area of Ethiopia where Lucy was found — has been dated to an age of 2.3 million years, Johanson said. He sees that as a sign that some primates in east Africa had completed the transition to Homo while others in southern Africa were still in the midst of that transition.

    "Right after 3 million years toward the present, we see that there is a response in eastern and southern Africa which are on two different evolutionary trajectories," Johanson said. One trajectory led to grass-eaters such as Paranthropus robustus and Paranthropus boisei, and the other trajectory led to bigger-brained species such as Homo ergaster, Homo rudolfensis and Homo habilis. He said Homo habilis appears to have existed in east Africa at the same time that australopiths in southern Africa were becoming more Homo-like.

    Courtesy of Lee Berger

    Anthropologist Lee Berger holds the cranium of Australopithecus sediba.

    "For the very first time, we've found the roots of Homo in south Africa, but it's too late to be the roots of Homo in east Africa," Johanson said.

    During a teleconference, Berger said it can be difficult to tease out the relationships between the various species along the evolutionary path leading to modern humans.

    "We're dealing with a period between, say, 2.3 million years and 1.6 milion years where the entire remainder of the fossil record could fit into a small shoebox, as opposed to these very well-preserved skeletons," Berger said. But he insisted that A. sediba "may very well be as good a model or better than the Homo habilis one, which actually only has a larger brain to go with it." He pointed out that our knowledge about Homo habilis was based on "very fragmentary fossils."

    Darryl de Ruiter, an anthropologist at Texas A&M University who is part of Berger's team, said researchers considered whether A. sediba represented nothing more than an evolutionary dead end. "But as we pointed out, and as all these papers are demonstrating, in every aspect of the skeleton — cranium, teeth, jaw, mandibles, hand, pelvis, foot, everything that we look at — we see characteristics that align this species more closely with Homo than any other australopith," he said.

    When the discovery of the A. sediba fossils was announced last year, Johanson speculated that the species might be more appropriately considered a part of the genus Homo than the genus Australopithecus. "I've actually changed my view," Johanson said. Now he agrees with Berger's team that it's an australopith. And who knows? Anthropologists may well change their minds many times as more fossils come to light.

    In any case, Johanson said, this week's revelations are "very, very interesting."

    "It does show that there are probably different ways of being an upright walker, and there are different ways of arranging the anatomy," he said. "There isn't just one strict way."

    More about human evolution:

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  • How big babies shaped society

    Getty Images file

    Relatively speaking, human babies are heavier than other infant primates - and that may have played a role in shaping us as social animals.

    By Alan Boyle, Science Editor, NBC News

    When it comes to size, human babies are more of a handful than other infant primates, and scientists say that may have played a role in shaping us as social animals.

    Now an anthropologist is making the case that the socialization process could have started much earlier than previously thought — perhaps more than 3 million years ago, when Lucy and her Australopithecus brethren roamed Africa.

    Boston University's Jeremy DeSilva came to that conclusion after running the numbers on bones from a wide variety of primate species, extinct and living, and determining that Australopithecus babies were probably just as much a handful for Lucy's kin as modern babies are for us. "I didn't expect to see that," he told me.

    DeSilva's findings were published online today in the Proceedings of the National Academy of Sciences.

    The idea behind DeSilva's research is that human mothers gave birth to relatively large babies, weighing roughly 6 percent of adult body mass. Chimpanzees and gorillas, in contrast, give birth to young that weigh 3 percent of the mother's body mass. "Carrying a relatively large infant both pre- and postnatally has important ramifications for birthing strategies, social systems, energetics and locomotion," DeSilva wrote.

    Scientists have long observed that bigger babies mean human mothers need more help than chimp mothers to give birth, take care of their babies and carry them around. In prehistoric times, that could have been a factor behind the development of extended family ties and other characteristics of human social organization. But how far back did that trend go?

    Guessing their weight
    DeSilva reviewed the body-mass studies for humans, chimps and gorillas — and he also gathered up bone measurements for extinct hominid species ranging from Homo erectus (which lived 700,000 to 1.8 million years ago) to Ardipithecus ramidus (which existed 4.4 million years ago).

    "Estimating infant body size when you don't have a body isn't easy," DeSilva acknowledged. He used estimates of the size of an adult hominid brain to come up with an estimate for the size of the brain at birth. Then he used a standard formula to extrapolate from the infant brain size to the total body mass. (A human infant's brain is 12 percent of body mass; for a chimp, the corresponding figure is 10 percent.) Finally, he used another statistical method, based on the load-bearing capacity of leg bones, to estimate the adult mass of the now-extinct hominids.

    DeSilva expected that the baby-size estimates would get bigger around the time of Homo erectus. But instead, the figures indicated that the weight of Australopithecus infants was 5 to 6 percent the weight of their moms.

    "The difference between a chimplike 3 percent and an estimated 5 or 6 percent is a big deal," DeSilva observied. "I think it's a pretty substantial cost to the mother."

    Going farther back on the evolutionary timeline, DeSilva found that Ardipithecus' weight estimates were more in line with the chimps, in the 2 to 3 percent range. Since Ardipithecus is seen as being close to the common ancestor of chimps and humans, the figures suggest that infant body proportions increased significantly by the time Lucy lived, 1.2 million years later.

    It takes a village?
    DeSilva speculated that Australopithecus babies would have been unable to walk on their own for their first 6 to 7 months. Their mothers would have faced the challenge of finding nutrients for themselves as well as breast-feeding the babies, "and would have benefited from the help of pair-bonded males, older children or siblings, or a combination of these."

    Getty Images

    A reconstruction shows how Lucy, a member of the species Australopithecus afarensis, might have looked 3.2 million years ago.

    "The expression that 'it takes a village to raise a child' may actually go back pretty far back into this Australopithecus group," DeSilva told me.

    Although the idea that Australopithecus was more of a social animal takes some getting used to, DeSilva said it actually fits with other evidence about the species' group behavior — including studies being done on the "First Family," a collection of fossils from at least 13 Australopithecus individuals found at a site in Ethiopia, near the place where Lucy was found. But DeSilva emphasized that much more study would be needed to confirm the relationship between bigger babies and social organization. 

    "The causality arrow on this, I'm not sure," he told me. "The data I played around with just shows that this group, Australopithecus, was birthing bigger kids than we thought. I think that has implications for reconstructing their biology."

    And it also has the effect of making Lucy, the 3.2 million-year-old creature who is thought to be our distant cousin, seem more ... well, more human. But what do you think? Does DeSilva's speculation make sense? Feel free to weigh in with your comments below.

    More about human origins:

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  • Can fingers point to sex habits?

    AAAS / Science file

    Researchers measured the length of fossilized fingers from Ardipithecus and other ancestors on humanity's family tree, then compared them with modern-day species in hopes of figuring out how aggressive and promiscuous long-gone species might have been.

    By Alan Boyle, Science Editor, NBC News

    The oldest-known species on humanity's family tree was built to be pushy and promiscuous, while another long-ago ancestor known as Lucy was lovey-dovey. Early humans and Neanderthals were more competitive than we are. At least those are the conclusions that researchers reached after sizing up the fingers of extinct and present-day primates.

    The study, published in the Proceedings of the Royal Society B, draws upon a famous and controversial indicator of social behavior: the comparative length of the index finger and the ring finger, also known as the 2D:4D ratio.

    If the ring finger is longer than the index finger, that's supposed to be correlated with higher prenatal exposure to androgens -- resulting in a higher proclivity for aggressiveness and promiscuity. The finger-length ratio also has been linked to sexual orientation as well as sporting prowess and musical ability.

    (Did you just look at your fingers?)

    Emma Nelson, an archaeologist from the University of Liverpool, extended the finger-length ratio study to a wide range of species. She and her colleagues measured bones from modern-day species such as gorillas, chimps, orangutans and the white-handed gibbon. They also looked at fossil bones or previously recorded measurements from extinct hominids ranging from Neanderthals (which co-existed with humans until about 30,000 years ago) to Australopithecus afarensis (Lucy's species, going back 3.1 million years) and Ardipithecus ramidus (the oldest human-linked fossil species, going back 4.4 million years).

    Nelson argues that comparing the finger-length ratios of extinct and present-day species is a valid technique for making an indirect assessment of our long-gone ancestors' social behavior.

    "It is believed that prenatal androgens affect the genes responsible for the development of fingers, toes and the reproductive system," she explained in a news release. "We have recently shown that promiscuous primate species have low index-to-ring finger ratios, while monogamous species have high ratios. We used this information to estimate the social behavior of extinct apes and hominins."

    Nelson previewed her findings a year ago at the Society of Vertebrate Paleontology's annual meeting, where she talked about naughty Neanderthals and monogamous australopiths. The newly published paper draws upon additional samples, including the finger lengths for Ardipithecus, or "Ardi." So here are the numbers:

    • Modern humans averaged a 0.957 index-to-ring finger ratio, and were considered to be on the line between a "pair-bonded," or monogamous, species and a middle-of-the-road species.
    • Chimps, gorillas and orangutans had index-to-ring ratios in the 0.90 to 0.92 range, and were classified as "non-pair-bonded," or promiscuous.
    • An early modern human from Israel's Qafzeh Cave, thought to be about 95,000 years old, had an index-to-ring ratio of 0.935. Based on that statistic, the researchers surmised this individual would be more promiscuous than modern humans.
    • The finger bones from five Neanderthals yielded a 0.928 ratio, associated with even greater competitiveness and promiscuity. Ardipithecus' bones took it up another notch, to 0.899. Two even older primate ancestors, Hispanopithecus and Pierolapithecus, had ratios of 0.848 and 0.908, which means they would have been tough to live with as well.
    • On the other end of the spectrum, the monogamous gibbons had a 1.009 ratio ... and the australopith sample came in with a ratio higher than that of modern-day humans (0.979). The implication, then, is that australopiths were monogamous.

    The big question is whether there's anything substantial to this analysis. Nelson acknowledged that the fossil record was sparse, and that more fossils were needed for study, but she insisted that "this method could prove to be an exciting new way of understanding how our social behavior has evolved."

    Other researchers have tried to make guesses about the social behavior of extinct hominid species by looking at sexual dimorphism -- that is, the differences between the male and the female of a species. If the males were significantly larger, the assumption is that they were built to have their way with many females in a promiscuous social setting. This has generated a fair amount of debate, particularly when it comes to assumptions about australopiths.

    Nelson and her colleagues suggest that the finger-length ratio could serve as an additional tool for making more educated guesses about ancient social behavior.

    "Social behaviors are notoriously difficult to identify in the fossil record," one of Nelson's fellow authors, the University of Oxford's Susanne Shultz, said in the news release. "Developing novel approaches, such as finger ratios, can help inform the current debate surrounding the social systems of the earliest human ancestors."

    When this research first came to light last year, University of Wisconsin anthropologist John Hawks cautioned against reading too much into fossilized fingers. He said the index-to-ring ratio "may be correlated with mating system in primates, but that doesn't mean it's a good predictor of mating system. ... As fossil hominins go, I wouldn't expect the story to go any further -- there just aren't many hands, so there's never going to be a significantly predictive result."

    Be sure to read Hawks' posting from last year, and feel free to weigh in with your comments below ... that is, after you've finished checking out your fingers.

    Update for 2 a.m. ET Nov. 3: John Hawks provided some additional thoughts in response to my e-mail inquiry:

    "The 2D:4D ratio really is a subject of a lot of research in psychology and developmental biology, and it really does reflect prenatal hormone exposure. However, it is not a good predictor of any social behaviors.

    "In addition to the problem of using a poor predictor, this study has another problem that we often face with fossils -- there are very few of them, and it's not obvious which sample of living primates we should be comparing with them.

    "The living apes do vary in mating structure, but they also have huge differences in hand anatomy because of locomotion. Those anatomical differences between species do not necessarily have any relationship to the neurological correlates of prenatal hormones -- even though the variation in hormone exposure is an important cause of variation within species.

    "For example, Ardipithecus has fingers and hand proportions that are right within the range of other apes. So when we see that they have a 2D:4D ratio right in the range of other apes, the natural hypothesis is that this reflects their overall hand proportions. Australopithecus, Neandertals and modern humans obviously had humanlike hand proportions, and their 2D:4D ratio may simply reflect this.

    "If you were going to do this study right, you would look far beyond the apes to take in many kinds of primates with different social systems. Then you could see whether closely related species have 2D:4D ratios that track their mating systems. Without this, we are really looking at a single evolutionary event -- the rise of the hominins -- which may be unique for many reasons besides mating system."

    In addition to Nelson and Shultz, the authors of "Digit Ratios Predict Polygyny in Early Apes, Ardipithecus, Neanderthals and Early Modern Humans but Not in Australopithecus"  include Campbell Rolian and Lisa Cashmore.

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  • How the penguin changed its feathers

    Katie Browne / UT-Austin

    The color scheme for the feathers of a 36 million-year-old penguin was likely different from what it is today, based on an analysis of fossil feathers.

    Katie Browne / UT-Austin

    The Inkayacu paracasensis skeleton suggests how ancient penguins gradually adapted to their aquatic environment.

    A 36 million-year-old fossil found in Peru suggests that the feathers of ancient giant penguins followed a different color scheme — and may not have been as hardy as they are today.

    Instead of sporting the classic tuxedo look of modern penguins, the fossil species known as Inkayacu paracasensis ("Water King of Paracas" in the Quechua language) had reddish brown and gray feathers, paleontologists report in a research paper published online today by the journal Science. The creature was nearly 5 feet tall, which outdoes the height of today's largest living penguin, the Emperor.

    "Before this fossil, we had no idea about the feathers, colors and flipper shapes of ancient penguins," lead author Julia Clarke, a paleontologist at the University of Texas at Austin, said in a news release. "We had questions, and this was our first chance to start answering them."

    The fossil was discovered by a Peruvian student, Ali Altamirano, in the Paracas National Reserve on the Peruvian coast south of Lima. When the researchers noticed that there was scaly soft tissue preserved on an exposed foot, they nicknamed the specimen "Pedro," after a sleazy, scaly character from a Colombian soap opera.

    The fossil preserved not only the shapes of Pedro's flippers and the feathers, but also the fine patterns of color-producing nanostructures known as melanosomes. Those patterns could be compared with a vast database of melanosome structures for living birds. The comparisons are what led Clarke and her colleagues to conclude that Pedro's color scheme was gray and red, because melanosomes with those colors matched the fossilized structures best.

    The shapes of the feathers and the flippers were very similar to what is seen in penguins today. But the patterns of the fossilized melanosomes had less in common with today's penguins and more in common with other types of aquatic birds. Modern-day penguins have giant melanosomes that are broader than the ones that were found in the giant penguin fossil. In fact, today's penguins have bigger melanosomes than the ones found in all the other living bird species that were surveyed. What's more, a modern penguin's melanosomes are grouped into clusters like bunches of grapes.

    This information led the researchers to put together the evolutionary story of how the penguin changed its feathers.

    They theorize that penguins initially adapted to their aquatic environment by developing strong, streamlined feathers that were stacked on top of each other to create stiff, narrow flippers. Then, long after Pedro bit the dust, the melanosomes took on larger sizes and a clustered arrangement. But why would the melanosomes change?

    It turns out that the coloring agent contained in the melanosomes, melanin, makes the feathers more resistant to wear and fracturing. Birds with bigger melanosomes would find it easier to keep their feathers in shape during those long, hard days of swimming.

    The color change itself might have been a side effect of the shift in melanosome structure, or it might have had more to do with a protective response to relatively recent predators as leopard seals. Maybe gray and red made the penguin stand out too much, compared with the more austere black-and-white scheme.

    "Insights into the color of extinct organisms can reveal clues to their ecology and behavior," said Yale University's Jakob Vinther, one of the research paper's co-authors. "But most of all, I think it is simply just cool to get a look at the color of a remarkable extinct organism, such as a giant fossil penguin."

    Update for 4 p.m. ET: As you can imagine, a lot of people are talking (and writing) about this story. Over at LiveScience, Stephanie Pappas quotes Gerald Mayr, a paleornithologist at the Senckenberg Museum of Natural History, as saying that the action of hydrodynamic forces on feathers may not totally explain why penguins evolved to have bigger melanosomes. He pointed out that a penguin's white feathers containe no melanosomes and yet would be subject to the same forces as the black ones. "The main question certainly is, if not due to hydrodynamic forces, why do penguins have such strange melanosomes?" he said.

    Ker Than's piece for National Geographic explains the modern penguin's camouflage: A swimming predator looking up from below would see the bird's white belly blending in with the sky, while the bird's black back would blend in with the dark watery depths when viewed from above. At Not Exactly Rocket Science, Ed Yong puts the Water King in context alongside other ancient penguins discovered in Paracas Park. Yong also links in turn to March of the Fossil Penguins, a blog which would have to be the definitive source on this subject. The blog's author? None other than Daniel Ksepka, one of the co-authors of the Science paper.

    More about penguins:


    In addition to Clark, Altamirano, Vinther and Ksepka, the authors of "Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers" include Rodolfo Salas-Gismondi, Matthew Shawkey, Liliana D'Alba, Thomas DeVries and Patrice Baby. The paper will appear later in Science's print edition. The National Geographic Society and the National Science Foundation provided funding for the research.

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  • How the 'terror bird' tore its prey

    Marcos Cenizo / Museo de la Plata

    In this artist's conception, the terror bird known as Andalgalornis brings its powerful beak down in a hatchetlike jab to attack its prey, a cat-sized herbivorous mammal called Hemihegetotherium. Andalgalornis was an extinct, 4.5-feet-tall, flightless predatory bird that lived in northwestern Argentina. Watch a computer animation of the terror bird's bite.

    Millions of years ago, the most fearsome predator in South America wasn't Tyrannosaurus rex or a raging mammoth - but a flightless bird with an enormous beak. The creatures known as "terror birds" held sway starting about 60 million years ago, and dominated the continent until only about 2 million years ago. But it wasn't clear exactly how the terror birds killed their prey. Until now.

    Paleontologists can now say with confidence that the terror birds, known formally as phorusrhacids, wielded their beaks like hatchets. They repeatedly hacked at their foes, rather than chomping at them and shaking them from side to side as T. rex might have done.

    These birds weren't built to wade into the fray like a feathered version of former boxing champ Joe Frazier. Instead, they took after Muhammad Ali, who famously defeated Frazier by floating like a butterfly and stinging like a ... well, like a terror bird.

    Paleontologists can say all this thanks to a detailed analysis of three-dimensional X-ray scans, documenting the structure of a terror bird's 6 million-year-old skull. The results were reported today in the open-access journal PLoS ONE.

    "One of the things that was surprising about this study is that we were actually able to find out quite a bit," one of the study's co-authors, Lawrence Witmer of the Ohio University College of Osteopathic Medicine, told me in advance of today's publication.

    Witmer has been studying the fossilized skulls of terror birds and other ancient creatures for some time now, trying to figure out how their brains worked. When he heard that other researchers were also looking into how terror birds did their thing, he linked up with them and providing the CT scans of a skull from a phorusrhacid species known as Andalgalornis. The scans allowed researchers to create a computer model suggesting what the skull was capable of doing ... as well as what it couldn't do.

    The skulls of modern-day birds have lots of light, mobile joints. Not so for the terror bird: "They evolutionarily transformed many of these joints into rigid, dense beams and struts," Witmer explained.

    The structure was optimized for a downward hacking motion of the beak. The bird could also conceivably bite down and crush its prey. But there was no way it could hang on and shake its victim from side to side. "It actually looked like that would cause catastrophic failure [of the skull], which is about as dramatic as it sounds," Witmer said.

    "A lot of animals just wade into battle, wrestle and battle to subdue their prey," he said. "That's pretty tough. What we found is that weakness from side to side really prevented these animals from doing that going into battle. Instead, it would attack and retreat, attack and retreat, making these almost surgical precision strikes."

    Once the terror bird felled its victim, it could tear the critter (most likely some sort of mammal) into bite-size pieces, or just swallow it whole.

    Other researchers behind the study - including the lead author, Federico Degrange of the Museo de la Plata/CONICET in Argentina - worked with zookeepers to study the bite strength of an eagle as well as a seriema, a bird thought to be the closest living relative of the terror bird. All the findings were consistent with the Muhammad Ali strategy.

    Degrange said the study provides the best explanation yet for why the terror bird was so terrible. "We need to figure out the ecological role that these amazing birds played if we really want to understand how the unusual ecosystems of South America evolved over the past 60 million years," he said in a news release about the research.

    Skulls compared

    Ohio University

    The fossil skull of the terror bird Andalgalornis is significantly larger than the skull of a modern-day golden eagle and a human skull. Andalgalornis lived 6 million years ago.

    Terror birds had few equals in their ecosystem. Witmer said its closest rival may well have been a saber-toothed marsupial known as Thylacosmilus. The bird that was analyzed for the PLoS ONE study stood about 4.5 feet (1.4 meters tall), but other terror birds are thought to have stood as tall as 7 feet (2.1 meters), dwarfing modern-day eagles. Most of them ranged over South America when it was an island continent, before its tectonic linkup with North America. At least one species, Titanis walleri, invaded North America millions of years ago in the Great American Interchange.

    The fall of the terror birds appears to have been as dramatic as its reign, but it's not yet clear exactly what caused them to go extinct. Paleontologists are pretty sure about one thing: Humans didn't kill them off. The birds may have been done in by big cats coming down into South America. Climate change may have played a role as well. "The extinction of successful animals is very rarely due to one factor, but a combination of events," zoologist Ross Piper observed in a posting on Scrubmuncher's Blog.

    Witmer said the study published today is a great example showing how paleontologists are "teasing everything we can out of these dusty bones."

    "Making these comparisons really starts to give us a broader view of what predators were like," he told me. "We're talking about a different world, a whole different dynamic. It's really a different window on the past, and terror birds wind up providing a pretty exciting view through that window."

    Watch a computer animation of the terror bird's bite. Join the Cosmic Log corps by signing up as my Facebook friend or hooking up on Twitter with @b0yle. And if you really want to be friendly, ask me about "The Case for Pluto."

  • Earliest traces of complex life?

    © El Albani - Mazurier

    A virtual reconstruction shows the outer (left) and inner (right) structure of a 2.1 billion-year-old fossil specimen from Gabon. Watch a TODAY video about the discovery.

    Scientists say they've discovered cookie-shaped fossils in Gabon that may represent the earliest-known multicellular life, dating back 2.1 billion years. But when you go that far back, claims about fossilized life get complicated.

    For one thing, we're talking about multicellular life: The traces of microbial life appear to go even further back in time - to 3.45 billion years ago, based on the way that mats of organic material have built up in ancient sediment. In the multicellular category, the oldest candidate has been a 2 billion-year-old, centimeter-scale, coil-shaped fossil known as Grypania spiralis, which might have been a giant bacterial or algal creature.

    The new discoveries, described in today's issue of the journal Nature, show more evidence of structure and measure as large as 12 centimeters (4.7 inches) in size. "On the surface, the fossils resemble irregularly shaped cookies with split edges and a lumpy interior," the researchers, led by Abderrarazak El Albani of the University of Poitiers, report in a news release.

    El Albani and his colleagues collected more than 250 fossils from a well-known geological formation in the West African country of Gabon, and put them through rounds of micro-CT scans to chart their 3-D structure. Based on that structure, the researchers deduce that the organisms were built up through cell-to-cell signaling - and not merely deposited together as a microbial mat.

    Gabon fossil

    © CNRS Photothèque / Kaksonen

    Many of the fossils found in Gabon measure more than an inch wide. Watch a video report about the discovery from TODAY's Dara Brown.

    "The relative complexity of the fossils ... lead El Albani and colleagues to conclude that they are unlike any living bacterium," Philip Donoghue and Jonathan Antcliffe of the University of Bristol write in a Nature commentary on the research. However, Donoghue and Antcliff say additional work will have to be done to confirm that these cookies are more than mere assemblages of one-celled organisms, as well as to verify they were living 2.1 billion years ago rather than during a later age.

    The 2.1 billion-year mark is significant because scientists think Earth's atmosphere made a major transition around 2.4 billion years ago. Before that time, there appears to have been no oxygen in the air. Even 2.1 billion years ago, "the atmosphere was still a toxic mix of greenhouse gases, with oxygen making up only a few percent of modern levels," Donoghue and Antcliff note.

    "This bacterial world was undergoing the greatest episode of climate change in the history of the planet: pumping out oxygen, drawing down carbon dioxide, slowly transforming the Earth into the world we know," they say.

    The bottom line is that these rock-hard cookies could shed light on how life as we generally know it arose from the alien-seeming, one-celled organisms that predated our planet's Great Oxidation Event. But this is still just a tiny piece in a puzzle that will take years of hard work to put together.

    In addition to El Albani, the authors of the Nature study, "Large Colonial Organisms With Coordinated Growth in Oxygenated Environments 2.1 Gyr Ago," include Stefan Bengtson, Donald E. Canfield, Andrey Bekker, Roberto Macchiarelli, Arnaud Mazurier, Emma U. Hammarlund, Philippe Boulvais, Jean-Jacques Dupuy, Claude Fontaine, Franz T. Fursich, Francois Gauthier-Lafaye, Philippe Janvier, Emmanuelle Javaux, Frantz Ossa Ossa, Anne-Catherine Pierson-Wickmann, Armelle Riboulleau, Paul Sardini, Daniel Vachard, Martin Whitehouse and Alain Meunier.

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  • Lucy's 'great-grandfather' found

    Dave Einsel / Getty Images file

    A sculptor's rendering shows how the 3.2-million-year-old hominid called Lucy might have looked in life. A more recently found fossil known as Kadanuumuu is from the same species, but 400,000 years older.

    Anthropologists say they have discovered the 3.6 million-year-old partial skeleton of a creature that came from the same species as Lucy, but was 400,000 years older and at least as good at walking upright. Their analysis suggests that upright walking, the trademark trait for humans and their extinct kin, goes back further in time than some might have assumed.

    This skeleton, described in the Proceedings of the National Academy of Sciences, has a much longer name than Lucy: It was dubbed Kadanuumuu, which means "big man" in Ethiopia's Afar language. Like the 3.3 million-year-old Lucy skeleton, Kadanuumuu was found in the East African country's Afar region, and shares the species name Australopithecus afarensis.

    Australopiths are fossil species that share some traits with chimpanzees - for instance, protruding faces and small brains - but share other traits with humans. Most importantly, their skeletons appear to have been built for upright walking. Arizona State University paleoanthropologist Donald Johanson, who discovered Lucy back in 1974, said the latest discovery adds to a "treasure trove" of hundreds of australopith fossils from East Africa.

    "It's like the El Dorado of paleoanthropology," he told me.

    Piecing together the evidence
    The first bone of Kadanuumuu's skeleton was found in 2005 in the Woranso-Mille area of the Afar region, about 30 miles north of where Lucy was discovered. Over the three years that followed, more than 30 additional bones were unearthed and pieced together for analysis.

    Hominid fossil

    CMNH / PNAS

    Elements of the partial australopith skeleton known as Kadanuumuu are arranged here anatomically.

    The head of the research team, Yohannes Haile-Selassie of the Cleveland Museum of Natural History, told me that Kadanuumuu's skeleton was clearly made for walking, based on measurements of bones including the limbs, clavicle and shoulder blade, the rib cage and the pelvis. In fact, its arrangement was better-suited for upright walking than Lucy's, even though it came from an earlier time in evolutionary history. The key measurement indicated that Kadanuumuu's lower limbs were more elongated than Lucy's - which would make walking easier.

    When Lucy was found, scientists thought her species was in the midst of a transition from tree-climbing to upright walking, but Kadanuumuu's larger skeleton suggests that the transition was already made hundreds of thousands of years earlier. (Haile-Selassie and his colleagues assume that Kadanuumuu was male, based on his size as well as the configuration of his pelvis.)

    "There is good grounds that advanced humanlike walking actually evolved long before people thought," Haile-Selassie said.

    So why did Lucy seem less-suited for upright walking? Haile-Selassie says it's because she was exceptionally small. Over the past 35 years, other specimens of Australopithecus afarensis have been found that suggested a body size larger than Lucy, and even larger than Kadanuumuu. "This individual is among the largest, but not the largest of all the specimens that we've found so far," Haile-Selassie said.

    Kadanuumuu is thought to have stood 5 to 5½ feet tall, while Lucy stood only 3½ feet tall. That's not unusual: Anthropologists have found that A. afarensis exhibited significant size differences between the male and the female of the species, a quality known as sexual dimorphism. The diminutive stature of Lucy, which is still the most complete australopith skeleton found to date, may have initially led some scientists down the wrong path, Haile-Selassie said. "Most of the misinterpretations were largely based on the size of Lucy and her sex," he told me.

    Findings fit in with ancient footprints
    If the conclusions made by Haile-Selassie and his colleagues are correct, the saga of how we became human is much more ancient than some might have thought. But in fact, the conclusions are consistent with another famous find, the 1976 discovery of the Laetoli footprints in Tanzania. Those prints, which were preserved in volcanic ash 3.6 million years ago, led scientists to suggest that upright walking was mastered well before Lucy's time. "What we have now is the skeletal evidence to complement those footprints," Haile-Selassie said.

    Johanson agreed. "This supports much of what we've known before" about the ability of australopiths to walk upright, he told me. He's not fully convinced, however, that Kadanuumuu was significantly better-built for walking than Lucy was. "I'm not quite sure they really have enough to say that the lower limb is elongated," he said.

    All this could lead anthropologists to look further back for the origins of upright walking. Perhaps Australopithecus anamensis, which lived in East Africa between 4.2 million and 3.9 million years ago, was the species that picked up the trick. Perhaps it all started with Ardipithecus ramidus, which is thought to have split its time between the trees and the ground in Ethiopia 4.4 million years ago (though there's some controversy over that claim).

    That doesn't mean Australopithecus afarensis is out of the spotlight when it comes to studying human origins. Johanson said Lucy and her kin provide an "important reference for assessing other hominid species," in large part because so many specimens have been found over such a wide span of evolutionary time. Going forward, paleoanthropologists may well turn to Lucy, Kadanuumuu and other members of the species to unravel the deeper secrets of ancient human development.

    "You can begin to look at the minutiae of microevolution over time," Johanson said, "which is where we're heading."

    More on the human origin story:

    In addition to Haile-Selassie, the authors of "An Early Australopithecus Afarensis Postcranium From Woranso-Mille, Ethiopia" include Bruce M. Latimer, Mulugeta Alene, Alan L. Deino, Luis Gilbert, Stephanie M. Melillo, Beverly Z. Saylor, Gary R. Scott and C. Owen Lovejoy.

    This report was last updated at 9 p.m. ET.

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