Partial skeleton from Lucy's species shows human ancestors walked like we do 3.6 million years ago
Meet Lucy's great-great-great grandfather.
On Monday, a team of Northeast Ohio researchers announced a rare and important find – the partial skeleton of a 3.6 million-year-old early human ancestor belonging to the same species as, but much older than, the iconic 3.2 million-year-old Lucy fossil discovered in 1974.
Less than 10 such largely intact skeletons 1.5 million years or older have been found. Greater Cleveland researchers have played leading roles in three of those discoveries, reinforcing the region's prominence in the search for humanity's origins.
The new specimen is called Kadanuumuu (pronounced Kah-dah-NEW-moo). The nickname means "big man" in the language of the Afar tribesmen who helped unearth his weathered bones from a hardscrabble Ethiopian plain beginning in 2005.
"Big" is an apt description of both Kadanuumuu's stature and his significance. The scientists who analyzed the long-legged fossil say it erases any doubts about stubby Lucy and her kind's ability to walk well on two legs, and reveals new information about when and how bipedality developed.
"It's all about human-like bipedality evolving earlier than some people think," said Cleveland Museum of Natural History anthropologist Yohannes Haile-Selassie, the lead author of the analysis appearing online in the journal Proceedings of the National Academy of Sciences. (To see a museum-produced video of Haile-Selassie describing the discovery, click here.)
"This is an incredible find," said Boston University paleoanthropologist Jeremy DeSilva, who was not involved in the discovery. "Researchers are going to be mining information from this skeleton for years and years. It raises a gazillion new and pretty exciting questions." Lucy still has the edge in celebrity status, with a three-decade head start and the advantage of being the first of her species to be found. But at 30 to 40 percent complete, Kadanuumuu is almost as intact as Lucy, and his skeleton includes some key parts, such as the shoulder blade, collar bone and much of the rib cage, that in Lucy did not survive the ravages of time.
Lucy "is always going to be the icon of her species," said Haile-Selassie. But with Kadanuumuu, "we have the most informative [skeletal] elements, the ones that can actually talk about function, biology, locomotion."
"I really tend to stay away from ranking things . . . [but] it certainly is an important specimen," said paleoanthropologist Donald Johanson, who discovered Lucy while serving as curator of physical anthropology at the Cleveland museum, the position Haile-Selassie now holds. Johanson now is at Arizona State University's Institute of Human Origins.
Johanson's team subsequently found parts of at least 13 other members of Lucy's species, Australopithecus afarensis. The fossil collection became known as the "First Family." Today scientists have more than 400 fossilized bones and teeth from various A. afarensis specimens, making it the best-known early human ancestor, but until now, there was no individual that rivaled the famous female skeleton's completeness.
At an estimated 5 to 5 1/2 feet tall, Kadanuumuu would have towered over the diminutive Lucy, who was nearly 2 feet shorter. Both were adults, but Lucy's tiny size, particularly her short legs, had caused some scientists to question whether she could easily and routinely walk upright – a pivotal development in evolution and the defining feature of the human lineage.
Kadanuumuu's relatively long legs, as well as some of its other anatomical features not preserved in Lucy's skeleton, show that members of the A. afarensis species could not only walk, but run, practically as well as modern humans do, say the study's authors. It's a claim that likely will be contentious.
"If Kadanuumuu were walking down the street and a human male were walking down the street, there might be a difference, but it would be really subtle," said Kent State University anthropologist Owen Lovejoy. The veteran scientist helped analyze the new partial skeleton, as he did with Lucy's remains three decades ago.
Kadanuumuu has "a very modern pelvis and it's 3.6 million years old," said Lovejoy, "which tells you that upright walking is really old." Also judging by its pelvis and the way the hamstring attached to it, "there's no doubt that this thing had a human-like style of running."
The only hitch might have been Kadanuumuu's left ankle, which was broken in childhood, judging by a scarred ring of knit bone. "It must have hurt like hell," said paleoanthropologist Bruce Latimer, a co-author of the new study and director of Case Western Reserve University's Center for Human Origins.
While scientists are virtually unanimous that Lucy and her kin walked upright in some fashion, there's been widespread and spirited disagreement about how well and how often the creatures did so.
One camp insists that the A. afarensis species, which lived in eastern Africa between 3 million and 3.7 million years ago, was anatomically "fully committed" to moving about on the ground, and did so with a striding, modern gait.
There's circumstantial evidence of that from the Laetoli footprints, a ghostly set of tracks left in wet volcanic ash by two, possibly three, individuals 3.6 million years ago, the same time that Kadanuumuu lived. The impressions were made in what is now northern Tanzania, about 1,100 miles from where Kadanuumuu was found.
The tracks show that the walkers, presumably Kadanuumuu's and Lucy's species, had arched foot bones, a vital shock-absorbing mechanism that enables long-distance walking. Chimpanzees and gorillas lack that adaptation.
This spring, researchers compared the Laetoli footprints to those of some test subjects walking normally, and others mimicking apes' bent-kneed, bent-hip step. Analysis of the footprints' weight-transfer patterns showed that the 3.6 million-year-old Laetoli walkers closely matched the extended-leg gait of modern humans.
The dissenting A. afarensis camp contends that Lucy and her relatives retained some skeletal remnants of their tree-dwelling ancestry – a sign they still spent time in the branches, and that their walking style while on the ground was much different and less efficient than ours.
Related disputes about the creatures' male-female body size, mating behavior and social organization have further divided the paleoanthropology community. Some have dubbed the standoff "the great afarensis wars."
Complicating matters is Lucy's small stature and odd proportions. Her short legs – much shorter than a human pygmy's – and relatively longer arms made her species seem chimp-like, an impression that couldn't be evaluated without something to compare her with.
"If you only have one individual, you have no appreciation for the variation in a population," DeSilva said. "Imagine if, a million years from now, the one skeleton that paleontologists find is Shaquille O'Neal's. Or Danny Devito's. You could have a very skewed look."
Hence, the debate.
"People have been arguing forever about did Lucy have short legs, did she have long arms," said Latimer. "The idea being that if Lucy had long arms, she was in the trees, and if she had short legs, she wasn't walking very well." Kadanuumuu clarifies things, the Cleveland researchers say.
It "has relatively long legs," Latimer said, "not as long as yours and mine, but longer than a chimp's and a gorilla's." Its rib cage is decidedly not ape-like, lacking the funnel shape that enables chimps and gorillas to pivot their shoulder downward to knuckle-walk. Kadanuumuu's shoulder blade – a fragile bone that rarely survives being buried for millions of years – looks much more human than ape-like.
Like "Ardi," the 4.4 million-year-old partial skeleton of an even older human ancestor unveiled last October by some of the same Cleveland researchers, Kadanuumuu reinforces the idea that chimps can't be used as the model for what we evolved from, even though they're our closest genetic relative.
Instead, the last common ancestor of chimps and humans seems to have been a tree-dwelling generalist whose body plan was more akin to a small monkey's. Chimps did a lot of changing after they split with our lineage 5 to 7 million years ago, the study's authors say.
"What Ardi tells us, and Kadanuumuu confirms, is that what chimpanzees and gorillas have done for their climbing ability is to greatly elongate their forelimbs and greatly abbreviate their hind limbs," Lovejoy said.
"Everyone thought that [human ancestors] started out with chimpanzee hind limbs and we really elongated them and it was this dramatic event in human evolution," Lovejoy said. "And it turns out it was not a major adaptation. "We didn't have to lengthen our hind limbs that much to get to modern proportions. They were never short."
That premise – that leg elongation was largely done by 3.6 million years ago, that modern bipedality was firmly in place, and that whatever leg lengthening took place later was not that important, evolution-wise – doesn't sit well with researchers such as William Jungers, a paleoanthropologist at New York's Stony Brook University.
As far back as 1982, Jungers published some of the earliest scientific doubts about Lucy's ability to walk as well as modern humans. While he praised Kadanuumuu as an important discovery, it hasn't changed his mind.
In an interview last week after reviewing the new research, Jungers said it shortchanges the considerable body alterations that took place after A. afarensis lived, a biped-boosting makeover that appeared only with the rise of our own family grouping, the genus Homo.
"What you see with the emergence of Homo erectus about 2 million years ago is quite a different skeletal design, and I don't think that's by chance," Jungers said. "You've got a reorganization that's telling us something new has happened in the adaptation for bipedality."
Those later, post-Lucy changes, which included more robust joints, taller, narrower bodies, wide shoulders, short toes, a more well-balanced head and bigger butt muscles, aided not only walking, but the advent of long-distance running, probably for hunting or scavenging, researchers Dan Lieberman of Harvard and Dennis Bramble of the University of Utah reported in 2004.
Lacking such adaptations, Kadanuumuu and his kind were still "good bipeds," Jungers said. "I just don't think they were identical in capabilities . . . to modern humans."
Without more fossils as old or older than Ardi, Lucy and Kadanuumuu for comparison, the afarensis wars will rage on.
Haile-Selassie will return to his native Ethiopia later this year in hopes of discovering them. The study area where his team unearthed Kadanuumuu's bones has exposed rocks both slightly younger and older than 3.6 million years which may contain more fossils, possibly even a new species different than A. afarensis.
For most researchers, finding a partial skeleton like Lucy is a career-capping moment. Haile-Selassie has done it twice now, spying Ardi's initial bones in the dirt in 1994 as a young graduate student, and identifying Kadanuumuu's arm in 2005.
"Maybe for some people it's not a once-in-a-lifetime experience," he mused. "There's no formula to finding a partial skeleton. It's just being at the right place at the right time."
Latimer, his colleague, isn't buying the chance angle. "Has this guy got the golden touch or what?" he said. "It's not luck any more."
On Monday, a team of Northeast Ohio researchers announced a rare and important find – the partial skeleton of a 3.6 million-year-old early human ancestor belonging to the same species as, but much older than, the iconic 3.2 million-year-old Lucy fossil discovered in 1974.
Less than 10 such largely intact skeletons 1.5 million years or older have been found. Greater Cleveland researchers have played leading roles in three of those discoveries, reinforcing the region's prominence in the search for humanity's origins.
The new specimen is called Kadanuumuu (pronounced Kah-dah-NEW-moo). The nickname means "big man" in the language of the Afar tribesmen who helped unearth his weathered bones from a hardscrabble Ethiopian plain beginning in 2005.
"Big" is an apt description of both Kadanuumuu's stature and his significance. The scientists who analyzed the long-legged fossil say it erases any doubts about stubby Lucy and her kind's ability to walk well on two legs, and reveals new information about when and how bipedality developed.
"It's all about human-like bipedality evolving earlier than some people think," said Cleveland Museum of Natural History anthropologist Yohannes Haile-Selassie, the lead author of the analysis appearing online in the journal Proceedings of the National Academy of Sciences. (To see a museum-produced video of Haile-Selassie describing the discovery, click here.)
"This is an incredible find," said Boston University paleoanthropologist Jeremy DeSilva, who was not involved in the discovery. "Researchers are going to be mining information from this skeleton for years and years. It raises a gazillion new and pretty exciting questions." Lucy still has the edge in celebrity status, with a three-decade head start and the advantage of being the first of her species to be found. But at 30 to 40 percent complete, Kadanuumuu is almost as intact as Lucy, and his skeleton includes some key parts, such as the shoulder blade, collar bone and much of the rib cage, that in Lucy did not survive the ravages of time.
Lucy "is always going to be the icon of her species," said Haile-Selassie. But with Kadanuumuu, "we have the most informative [skeletal] elements, the ones that can actually talk about function, biology, locomotion."
"I really tend to stay away from ranking things . . . [but] it certainly is an important specimen," said paleoanthropologist Donald Johanson, who discovered Lucy while serving as curator of physical anthropology at the Cleveland museum, the position Haile-Selassie now holds. Johanson now is at Arizona State University's Institute of Human Origins.
Johanson's team subsequently found parts of at least 13 other members of Lucy's species, Australopithecus afarensis. The fossil collection became known as the "First Family." Today scientists have more than 400 fossilized bones and teeth from various A. afarensis specimens, making it the best-known early human ancestor, but until now, there was no individual that rivaled the famous female skeleton's completeness.
At an estimated 5 to 5 1/2 feet tall, Kadanuumuu would have towered over the diminutive Lucy, who was nearly 2 feet shorter. Both were adults, but Lucy's tiny size, particularly her short legs, had caused some scientists to question whether she could easily and routinely walk upright – a pivotal development in evolution and the defining feature of the human lineage.
Kadanuumuu's relatively long legs, as well as some of its other anatomical features not preserved in Lucy's skeleton, show that members of the A. afarensis species could not only walk, but run, practically as well as modern humans do, say the study's authors. It's a claim that likely will be contentious.
"If Kadanuumuu were walking down the street and a human male were walking down the street, there might be a difference, but it would be really subtle," said Kent State University anthropologist Owen Lovejoy. The veteran scientist helped analyze the new partial skeleton, as he did with Lucy's remains three decades ago.
Kadanuumuu has "a very modern pelvis and it's 3.6 million years old," said Lovejoy, "which tells you that upright walking is really old." Also judging by its pelvis and the way the hamstring attached to it, "there's no doubt that this thing had a human-like style of running."
The only hitch might have been Kadanuumuu's left ankle, which was broken in childhood, judging by a scarred ring of knit bone. "It must have hurt like hell," said paleoanthropologist Bruce Latimer, a co-author of the new study and director of Case Western Reserve University's Center for Human Origins.
While scientists are virtually unanimous that Lucy and her kin walked upright in some fashion, there's been widespread and spirited disagreement about how well and how often the creatures did so.
One camp insists that the A. afarensis species, which lived in eastern Africa between 3 million and 3.7 million years ago, was anatomically "fully committed" to moving about on the ground, and did so with a striding, modern gait.
There's circumstantial evidence of that from the Laetoli footprints, a ghostly set of tracks left in wet volcanic ash by two, possibly three, individuals 3.6 million years ago, the same time that Kadanuumuu lived. The impressions were made in what is now northern Tanzania, about 1,100 miles from where Kadanuumuu was found.
The tracks show that the walkers, presumably Kadanuumuu's and Lucy's species, had arched foot bones, a vital shock-absorbing mechanism that enables long-distance walking. Chimpanzees and gorillas lack that adaptation.
This spring, researchers compared the Laetoli footprints to those of some test subjects walking normally, and others mimicking apes' bent-kneed, bent-hip step. Analysis of the footprints' weight-transfer patterns showed that the 3.6 million-year-old Laetoli walkers closely matched the extended-leg gait of modern humans.
The dissenting A. afarensis camp contends that Lucy and her relatives retained some skeletal remnants of their tree-dwelling ancestry – a sign they still spent time in the branches, and that their walking style while on the ground was much different and less efficient than ours.
Related disputes about the creatures' male-female body size, mating behavior and social organization have further divided the paleoanthropology community. Some have dubbed the standoff "the great afarensis wars."
Complicating matters is Lucy's small stature and odd proportions. Her short legs – much shorter than a human pygmy's – and relatively longer arms made her species seem chimp-like, an impression that couldn't be evaluated without something to compare her with.
"If you only have one individual, you have no appreciation for the variation in a population," DeSilva said. "Imagine if, a million years from now, the one skeleton that paleontologists find is Shaquille O'Neal's. Or Danny Devito's. You could have a very skewed look."
Hence, the debate.
"People have been arguing forever about did Lucy have short legs, did she have long arms," said Latimer. "The idea being that if Lucy had long arms, she was in the trees, and if she had short legs, she wasn't walking very well." Kadanuumuu clarifies things, the Cleveland researchers say.
It "has relatively long legs," Latimer said, "not as long as yours and mine, but longer than a chimp's and a gorilla's." Its rib cage is decidedly not ape-like, lacking the funnel shape that enables chimps and gorillas to pivot their shoulder downward to knuckle-walk. Kadanuumuu's shoulder blade – a fragile bone that rarely survives being buried for millions of years – looks much more human than ape-like.
Like "Ardi," the 4.4 million-year-old partial skeleton of an even older human ancestor unveiled last October by some of the same Cleveland researchers, Kadanuumuu reinforces the idea that chimps can't be used as the model for what we evolved from, even though they're our closest genetic relative.
Instead, the last common ancestor of chimps and humans seems to have been a tree-dwelling generalist whose body plan was more akin to a small monkey's. Chimps did a lot of changing after they split with our lineage 5 to 7 million years ago, the study's authors say.
"What Ardi tells us, and Kadanuumuu confirms, is that what chimpanzees and gorillas have done for their climbing ability is to greatly elongate their forelimbs and greatly abbreviate their hind limbs," Lovejoy said.
"Everyone thought that [human ancestors] started out with chimpanzee hind limbs and we really elongated them and it was this dramatic event in human evolution," Lovejoy said. "And it turns out it was not a major adaptation. "We didn't have to lengthen our hind limbs that much to get to modern proportions. They were never short."
That premise – that leg elongation was largely done by 3.6 million years ago, that modern bipedality was firmly in place, and that whatever leg lengthening took place later was not that important, evolution-wise – doesn't sit well with researchers such as William Jungers, a paleoanthropologist at New York's Stony Brook University.
As far back as 1982, Jungers published some of the earliest scientific doubts about Lucy's ability to walk as well as modern humans. While he praised Kadanuumuu as an important discovery, it hasn't changed his mind.
In an interview last week after reviewing the new research, Jungers said it shortchanges the considerable body alterations that took place after A. afarensis lived, a biped-boosting makeover that appeared only with the rise of our own family grouping, the genus Homo.
"What you see with the emergence of Homo erectus about 2 million years ago is quite a different skeletal design, and I don't think that's by chance," Jungers said. "You've got a reorganization that's telling us something new has happened in the adaptation for bipedality."
Those later, post-Lucy changes, which included more robust joints, taller, narrower bodies, wide shoulders, short toes, a more well-balanced head and bigger butt muscles, aided not only walking, but the advent of long-distance running, probably for hunting or scavenging, researchers Dan Lieberman of Harvard and Dennis Bramble of the University of Utah reported in 2004.
Lacking such adaptations, Kadanuumuu and his kind were still "good bipeds," Jungers said. "I just don't think they were identical in capabilities . . . to modern humans."
Without more fossils as old or older than Ardi, Lucy and Kadanuumuu for comparison, the afarensis wars will rage on.
Haile-Selassie will return to his native Ethiopia later this year in hopes of discovering them. The study area where his team unearthed Kadanuumuu's bones has exposed rocks both slightly younger and older than 3.6 million years which may contain more fossils, possibly even a new species different than A. afarensis.
For most researchers, finding a partial skeleton like Lucy is a career-capping moment. Haile-Selassie has done it twice now, spying Ardi's initial bones in the dirt in 1994 as a young graduate student, and identifying Kadanuumuu's arm in 2005.
"Maybe for some people it's not a once-in-a-lifetime experience," he mused. "There's no formula to finding a partial skeleton. It's just being at the right place at the right time."
Latimer, his colleague, isn't buying the chance angle. "Has this guy got the golden touch or what?" he said. "It's not luck any more."
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