CMNH hominid timeline
New York Times
The Upright Ape by Aaron Filler
``Museum Scientists Play Key Role in Discovery, Analysis of Early Human Ancestor
Scientists from The Cleveland Museum of Natural History and Case Western Reserve University were part of an international team that discovered and published new research describing the 4.4 million-year-old hominid species Ardipithecus ramidus.
Working in the Afar Rift of Ethiopia since 1981, the Middle Awash research team found a partial skeleton of a female Ardipithecus ramidus in 1994. The specimen was found by Dr. Yohannes Haile-Selassie, curator and head of physical anthropology at The Cleveland Museum of Natural History. Nicknamed "Ardi," the specimen is the earliest skeleton known from the human branch of the primate family tree. Its discovery provides new insights into human evolution.
The Middle Awash paleoanthropological research project, which includes Dr. Yohannes Haile-Selassie; Dr. Scott Simpson, associate professor, Case Western Reserve University, Department of Anatomy, School of Medicine; and Dr. Bruce Latimer, associate professor, Case Western Reserve University, Department of Anthropology, excavated "Ardi" for three continuous field seasons and recovered key specimens of the partial skeleton, including the skull with teeth, arms, hands, pelvis, legs and feet. Dr. Linda Spurlock, director of human health at The Cleveland Museum of Natural History, created a sculpture reconstruction of the hominid's pelvis.
The Middle Awash paleoanthropological research project is led by Dr. Tim White of the University of California, Berkeley.
Following years of analysis, results from the team's research will be published in the October 2, 2009 special issue of Science in the form of 11 detailed, peer-reviewed papers and general summaries.
Science Cover Image Caption: Partial skeleton of Ardipithecus ramidus, a hominid species living about 4.4 million years ago in Ethiopia. This female stood about 1.2 meters high. Eleven papers from an international team of authors published in print and online in this special issue describe the anatomy of this species and its habitat and discuss the implications for understanding human evolution. One result is that extant great apes are poor models for our last common ancestor with chimpanzees.''
The Cleveland Museum of Natural History | 1 Wade Oval Drive University Circle Cleveland OH 44106-1767 U.S.A. | 216.231.4600 | 800.317.9155
``1974 Dr. Donald Johansen, then Curator of Physical Anthropology, discovers a partial skeleton of a more than 3 million years old female in Ethiopia. He nicknamed her "Lucy." In 1997, scientists prove that the fossils were a new hominid species described as Australopithecus afarensis.
1999 Dr. Bruce Latimer, Curator of Physical Anthropology, is a member of an international team who publish an article in the journal Science about a new hominid species, Australopithecus garhi, which they discovered at Bouri on the Middle Awash River in Ethiopia.
2004 Curator of Physical Anthropology Dr. Yohannes Haile-Selassie and his scientific team working in the Middle Awash valley of the Afar Region in Ethiopia have found dental evidence that Ardipithecus kadabba was the earliest species of its genus, dating between 5.54 and 5.77 million years ago.
2005 Dr. Yohannes Haile-Selassie, head of a scientific team working in Korsi-Dora in the vicinity of Mille town located in the Northern Afar Region, along with his colleagues, have found a partial fossil skeleton of a hominid that is probably around 3.8 to 4 million years old, based on associated animal remains. Drs. Yohannes Haile-Selassie and Bruce Latimer lead a team to Ethiopia and discover 12 early hominid fossil specimens from four localities in Afar Region.''
ARTICLE from The New York Times, 10-1-09, By JOHN NOBLE WILFORD
``Fossil Skeleton From Africa Predates Lucy
Lucy, meet Ardi.
A fairly complete skeleton of Ardipithecus ramidus, which replaced Lucy as the earliest known skeleton from the human branch of the primate family tree. More Photos »
Ardi, short for Ardipithecus ramidus, is the newest fossil skeleton out of Africa to take its place in the gallery of human origins. At an age of 4.4 million years, it lived well before and was much more primitive than the famous 3.2-million-year-old Lucy, of the species Australopithecus afarensis.
Since finding fragments of the older hominid in 1992, an international team of scientists has been searching for more specimens and on Thursday presented a fairly complete skeleton and their first full analysis. By replacing Lucy as the earliest known skeleton from the human branch of the primate family tree, the scientists said, Ardi opened a window to "the early evolutionary steps that our ancestors took after we diverged from our common ancestor with chimpanzees."
The older hominid was already so different from chimps that it suggested "no modern ape is a realistic proxy for characterizing early hominid evolution," they wrote.
[In other words, the great apes branched off from our line of descent. We did not descend from the great apes. who could only partially go from being bipeds to being quadripeds with knuckle walking.]
The Ardipithecus specimen, an adult female, probably stood four feet tall and weighed about 120 pounds, almost a foot taller and twice the weight of Lucy. Its brain was no larger than a modern chimp's. It retained an agility for tree-climbing but already walked upright on two legs, a transforming innovation in hominids, though not as efficiently as Lucy's kin.
Ardi's feet had yet to develop the arch-like structure that came later with Lucy and on to humans. The hands were more like those of extinct apes. And its very long arms and short legs resembled the proportions of extinct apes, or even monkeys.
Tim D. White of the University of California, Berkeley, a leader of the team, said in an interview this week that the genus Ardipithecus appeared to resolve many uncertainties about "the initial stage of evolutionary adaptation" after the hominid lineage split from that of the chimpanzees. No fossil trace of the last common ancestor, which lived some time before six million years ago, according to genetic studies, has yet come to light.
The other two significant stages occurred with the rise of Australopithecus, which lived from about four million to one million years ago, and then the emergence of Homo, our own genus, before two million years ago. The ancestral relationship of Ardipithecus to Australopithecus has not been determined, but Lucy's australopithecine kin are generally recognized as the ancestral group from which Homo evolved.
Scientists not involved in the new research hailed its importance, placing the Ardi skeleton on a pedestal alongside notable figures of hominid evolution like Lucy and the 1.6-million-year-old Turkana Boy from Kenya, an almost complete specimen of Homo erectus with anatomy remarkably similar to modern Homo sapiens ...
The first comprehensive reports describing the skeleton and related findings, the result of 17 years of study, are being published Friday in the journal Science. Eleven papers by 47 authors from 10 countries describe the analysis of more than 110 Ardipithecus specimens from a minimum of 36 different individuals, including Ardi.
The paleoanthropologists wrote in one of the articles that Ardipithecus was "so rife with anatomical surprises that no one could have imagined it without direct fossil evidence."
A bounty of animal and plant material -- "every seed, every piece of fossil wood, every scrap of bone," Dr. White said -- was gathered to set the scene of the cooler, more humid woodland habitat in which these hominids had lived.
This was one of the first surprises, said Giday WoldeGabriel, a geologist at Los Alamos National Laboratory, because it upset the hypothesis that upright walking had evolved as an adaptation to life on grassy savanna.
This article has been revised to reflect the following correction:
Correction: October 13, 2009 An article on Oct. 2 about fossils of a new human ancestor, Ardipithecus ramidus, described incorrectly the contribution of C. Owen Lovejoy, an anatomist at Kent State University, to the 11 reports on the fossils published that day in the journal Science. Dr. Lovejoy was the lead author of five of the journal reports, not two.''
ARTICLE from Science News, January 16th, 2010; Vol.177, #2 (p. 22), By Bruce Bower
``Evolution's Bad Girl Ardi shakes up the fossil record
Standing tallIn this artist's illustration, Ardi stands amid Ardipithecus ramidus comrades in once-forested East Africa.Illustration: Jay Matternes
She's the ultimate evolutionary party crasher. Dubbed Ardi, her partial skeleton was unearthed in Ethiopia near the scattered remains of at least 36 of her comrades. Physical anthropologists had known about the discovery of this long-gone gal for around 15 years, but few expected to see the 4.4-million-year-old hell-raiser that was unveiled in 11 scientific papers in October.
Like a biker chick strutting into a debutante ball, Ardi brazenly flaunts her nonconformity among more-demure members of the human evolutionary family, known as hominids. She boasts a weird pastiche of anatomical adornments, even without tattoos or nose studs. In her prime, she moved slowly, a cool customer whether upright or on all fours. Today, she's the standard bearer for her ancient species, Ardipithecus ramidus.
And in true biker-chick fashion, Ardi chews up and spits out conventional thinking about hominid origins, according to a team -- led by anthropologist Tim White of the University of California, Berkeley -- that unearthed and analyzed her fragile bones (SN: 10/24/09, p. 9).
First, White and his colleagues assert, Ardi's unusual mix of apelike and monkeylike traits demolishes the long-standing assumption that today's chimpanzees provide a reasonable model of either early hominids or the last common ancestor of people and chimps -- an ancestor which some scientists suspect could even have been Ardi, if genetics-based estimates of when the split occurred are borne out.
Second, the team concludes, Ardi trashes the idea that knuckle-walking or tree-hanging human ancestors evolved an upright gait to help them motor across wide ancient savannas. Her kind lived in wooded areas and split time between lumbering around on two legs hominid-style and cruising carefully along tree branches on grasping feet and the palms of the hands.
One member of White's team argues for a controversial possibility: that two-legged walking evolved because Ardipithecus males had small canine teeth. Many living and fossil male apes fight for mates by wielding formidable canines, but Ardi's male counterparts had to band together and forage over long distances to obtain mates, his thinking goes.
In a third slap at scientific convention, Ardi fits a scenario in which a few closely related hominid lineages preceded the larger-brained Homo genus that emerged around 2.4 million years ago, White says. In contrast, many anthropologists think of hominid evolution as a bush composed of numerous lineages that, for the most part, died out.
Each of Ardi's challenges draws plenty of fire. While lauding the new finds and the painstaking reconstruction of Ardi's bony frame, some critics dismiss White and company's reading of the fossils as incomplete and speculative.
Presentations at the Royal Society of London in October by several members of the Ardi excavation team produced "much sparring," says anthropologist William McGrew of the University of Cambridge in England.
"There's legitimate disagreement," White says. "But Ardi provides a perspective on early hominid evolution that was previously missing. This is a really bizarre primate."
Ardi sports a peculiar skeletal medley that pushes chimps and gorillas out of the evolutionary spotlight, says anthropologist Owen Lovejoy, a member of White's team. Ardi's ancient remains indicate that the last common ancestor of humans and chimps must not have looked much like living chimps, as many researchers have assumed, asserts Lovejoy, of Kent State University in Ohio.
Since a split 8 million years ago or so, chimps and gorillas have evolved along evolutionary paths that eventually produced specialized traits such as knuckle-walking, he says.
In his opinion, Ardi indicates that a human-chimp ancestor had monkeylike limb proportions and feet, a flexible and unchimplike lower back, and an ability to move along tree branches on all fours, rather than swinging chimp-style from branch to branch and hanging by outstretched arms.
"Ardipithecus, not living chimps, offers a remarkably good perspective on the last common ancestor," he says. "We can't modify the truth to make chimps more important." ...
Questions remain about whether Ardi had the build for regular upright walking -- a clear marker of hominid status -- or for primarily moving through trees, with occasional two-legged jaunts on the ground, adds anthropologist John Hawks of the University of Wisconsin, Madison.
Consider Oreopithecus, an ape that lived on an island near Italy between 9 million and 7 million years ago. This creature possessed a pelvis, legs and feet that supported tree climbing as well as slow and somewhat stilted walking.
"Oreopithecus shows that there are alternate pathways to evolving a ground-based skeleton from the ape body plan," Hawks says.
But Oreopithecus differed from Ardi in critical ways, Lovejoy responds, such as having extremely long arms. "Locomotion differed vastly between Oreopithecus and Ardi," he says.
If Ardipithecus adopted upright walking in a big way and was a precursor of the human lineage, Hawks posits, "it could be the first hominid or perhaps even the common ancestor of humans and chimps -- if we take genetic studies seriously." DNA analyses suggest that people and chimps split from a common ancestor between 5 million and 4.5 million years ago, around Ardi's time.
Lovejoy regards those genetic estimates as unreliable. DNA studies rest on doubtful assumptions, he says, such as constant rates of genetic mutation in the human and chimp lineages. Fossil evidence places the human-chimp split at more like 8 million to 10 million years ago, in his view.
Hominid family values
Disputes over Ardi's evolutionary relationships to living and extinct apes seem cordial compared with debate over her sexual relationships and their implications for ancient hominid social life.
This fracas goes back to 1981, when Lovejoy published a paper in Science about the sex life of what was, at that time, the earliest known hominid species, Australopithecus afarensis.
The most famous member of that species is Lucy, a 3.2-million-year-old partial female skeleton found at another Ethiopian site in 1974. Lovejoy proposed that Lucy's kind possessed traits consistent with what amounted to a sexual revolution in the ape world (SN: 6/11/05, p. 379).
In most ape species, males are much larger than females and fight viciously to mate with fertile females, who advertise their availability with swollen red tissue. Females raise offspring on their own.
Lucy's kind upended that arrangement, Lovejoy argued. Males grew only slightly larger than females and had small canines. Adults of both sexes favored long-term relationships as a matter of survival, he theorized. Males supplied food to regular partners with whom they had children, allowing females to spend more time raising their own children.
Monogamy worked, in Lovejoy's view, because female anatomy evolved to mask obvious signs of ovulation that signal sexual readiness to males, instead developing features such as permanently enlarged breasts. Hit-and-run unions stood a good chance of yielding no offspring and thus became unappealing to both sexes.
Lovejoy's evidence for minimal size differences between A. afarensis sexes has been sharply criticized. Critics charge that he's underestimated the size disparities.
Detractors add that upright males with diminutive canines could have found plenty of ways to pummel one another in mating battles, even if they had to resort to fisticuffs.
With Ardi in tow, Lovejoy has now elaborated on his argument. A transition to monogamous relationships, expanded child care by mothers and hidden female ovulation first occurred before Lucy, in Ardipithecus, he proposes. Ardi's kind displays even smaller sex differences in canine size than Lucy's species. "Australopithecus represents a more intense version of what was already evolving in Ardipithecus," Lovejoy says.
Cooperation among males later expanded in A. afarensis, he posits. Male bands scoured forests and savannas for food and worked together to avoid and defend against predators.
A social puzzle
Ardipithecus canines excavated by White's team validate Lovejoy's scenario, remarks anthropologist Robert Tague of Louisiana State University in Baton Rouge. Male canines are slightly larger than those of females, but all the canines are about the size of female chimps' canines, he says.
"Although Lovejoy's theory is widely cited and presented in almost all biological anthropology textbooks, it is also widely rejected," Tague acknowledges.
And for good reason, argues J. Michael Plavcan of the University of Arkansas in Fayetteville. Using a different statistical approach, he estimates that Lucy was actually considerably smaller than her male cohorts.
To portray early hominids as a peaceful, monogamous crowd "is phenomenally speculative," Plavcan says. Although large-bodied primate males with fanglike canines usually fight over mates, minimal sex differences can result in any of a variety of mating arrangements, he contends.
What's more, Ardipithecus ramidus fossils do display size differences between the sexes sufficient to assume that males mated with several females, as in many other primates with size disparities, McGrew remarks.
"Lovejoy's social hypothesis is an interesting just-so story," Richmond asserts. "He's winning the competition for the title of the Rudyard Kipling of paleoanthropology."
Primatologist Frans de Waal of Emory University in Atlanta doesn't dismiss Lovejoy's social hypothesis but faults him for comparing Ardi's kind with common chimps while ignoring pygmy chimps, or bonobos. Bonobos have small canines relative to common chimps, a largely peaceful social life and a fondness for sexual activity.
"It's high time for a new look at the bonobo," de Waal wrote in a published commentary shortly after the Ardi papers appeared in Science. "What if we descend not from a blustering chimplike ancestor but from a gentle, empathic, bonobo-like ape?"
That's doubtful, since bonobos differ in some critical ways from Ardi's kind, Lovejoy responds. In particular, he says, bonobo males display moderately larger canines and body sizes than females.
"Ardipithecus ramidus preserves some of the ancestral characteristics of the last common ancestor (of humans and chimps) with much greater fidelity than does any living African ape," Lovejoy says.
If Ardi cuts a singular figure that sets her apart from living apes, she also bolsters an argument for cutting back the expanding number of proposed early hominid lineages, White says. Since 1994, fossil discoveries have led to reports of four new genera from eastern Africa and Chad:
7-million to 6-million-year-old Sahelanthropus (SN: 7/13/02, p. 19),
6-million-year-old Orrorin (SN: 7/14/01, p. 20),
3.5-million-year-old Kenyanthropus (SN: 3/24/01, p. 180)
and Ardipithecus, including fragmentary remains of 5.8-million to 5.2-million-year-old Ardipithecus kadabba.
White's team folds Sahelanthropus, known only from skull remains, and Orrorin, known from fossil teeth and leg-bone pieces, into the better-described Ardipithecus genus.
"Ardipithecus may represent a long period of stasis in hominid evolution," Lovejoy says.
From about 6 million to 4.2 million years ago, he proposes, Ardipithecus evolved as a set of separate hominid groups in East Africa that interbred enough to maintain biological unity.
After that, Ardi's kind possibly evolved into the first Australopithecus species. Or, one Ardipithecus group may have settled in an isolated area where it alone evolved into Australopithecus. It's also possible that Australopithecus derived from a hominid lineage that researchers haven't found, relegating Ardipithecus to an evolutionary side branch.
Anthropologists, in particular those who have excavated and named other early hominid genera, have not jumped on the Ardipithecus bandwagon. Proponents of bushy hominid evolution, such as Richmond, rely on computerized models that divvy up species by distinguishing between shared and distinctive skeletal traits across fossil sets, an approach that White and Lovejoy have criticized (SN: 11/25/00, p. 346).
"More time is needed to study Ardi and compare her to living primates," Hawks says. "White's team had 15 years to study this skeleton that the rest of us saw for the first time in October."
Complaints have circulated in anthropological circles over the past decade that White has inappropriately kept outside investigators from studying Ardi's remains. White vehemently denies those charges, saying that he has abided by Ethiopian law by publishing an initial description of the finds before making them available for others to study.
Researchers can now examine casts of the Ardipithecus fossils or, in certain cases, the fragile bones themselves, White says.
"These finds are phenomenally important and will keep many of us busy for years to come," says anthropologist Carol Ward of the University of Missouri in Columbia.
In other words, the evolutionary shindig that Ardi crashed has just started. The night is young. Party hearty, Ardi.
Bower, B. 2009. Aping the Stone Age. Science News 176(Nov. 21):24.
Bower, B. 2009. Partial skeleton gives ancient hominids a new look. Science News 176(Oct. 24):9.
Bower, B. 2005. Faithful ancestors. Science News 167(June 11):379.
Bower, B. 2002. Evolution's surprise: Fossil find uproots our early ancestors. Science News 162(July 13):19.
Bower, B. 2001. Fossil skull diversifies family tree. Science News 159(March 24):180.
Bower, B. 2000l. Out on a limb. Science News 158(Nov. 25):346.
Lovejoy, O. 1981. The origin of man. Science 211:341 Bower, B. 2001. Earliest Ancestor Emerges in Africa. Science News
Citations & References:
White, T., et al. 2009. Ardipithecus ramidus and the paleobiology of early hominids. Science 326:75. doi:10.1126/science.1175802
Lovejoy, O. 2009. Reexamining human origins in light of Ardipithecus ramidus. Science 326:74e1. doi:10.1126/science.1175834
Suwa, G., et al. 2009. The Ardipithecus ramidus skull and its implications for hominid origins. Science 326:68e1. doi:10.1126/science.1175825
Lovejoy, O., et al. 2009. Careful climbing in the miocene: The forelimbs of Ardipithecus ramidus and humans are primitive. Science 326:70e1. doi:10.1126/science.1175827
Lovejoy, O., et al. 2009. The pelvis and femur of Ardipithecus ramidus: The emergence of upright walking. Science 326:71e1. doi:10.1126/science.1175831
Lovejoy, O., et al. 2009. Combining prehension and propulsion: The foot of Ardipithecus ramidus. Science 326:72e1. doi:10.1126/science.1175832
Suwa, G., et al. 2009. Paleobiological implications of the Ardipithecus ramidus dentition. Science 326:94. doi:10.1126/science.1175824
Lovejoy, O., et al. 2009. The great divides: Ardipithecus ramidus reveals the postcrania of our last common ancestors with African apes. Science 326:100. doi:10.1126/science.1175833
White, T., et al. 2009. Macrovertebrate paleontology and the pliocene habitat of Ardipithecus ramidus. Science 326:87. doi:10.1126/science.1175822
Louchart, A., et al. 2009. Taphonomic, avian, and small-vertebrate IIndicators of Ardipithecus ramidus habitat. Science 326:66e1. doi:10.1126/science.1175823
WoldeGabriel, G., et al. 2009. The geological, isotopic, botanical, invertebrate, and lower vertebrate surroundings of Ardipithecus ramidus. Science 326:65e1. doi:10.1126/science.1175817. Special issue on Ardipithecus. Science. October 2, 2009.''
Excerpt from "The Upright Ape: A New Origin of the Species"
by Aaron G. Filler MD, PhD
``An Upright Ancestor for the Apes
The discovery of an ancient fossil in Moroto, Uganda from 21 million years ago was the first sign of a major flaw in our models of human evolution. It is almost identical to a modern human lumbar vertebra.
But it was just one fossil against a world full of scientific opinion that humans, with their upright bipedal walking did not emerge until the chimpanzee-human split 6 million years ago.
Then fossils of another upright bipedal ape - Oreopithecus - were found. Then another - Pierolapithecus. And then Sahelanthropus.
First there was one. Now there are four upright bipedal species of apes before the chimp-human split.
Paleoanthropology as a field has not yet come to grips with the revolutionary implications. The first "human" was probably Morotopithecus and probably lived 21 million years ago. The existing apes have a human ancestor.
For fifty years we have defined the first humans by the acquisition of upright bipedal posture in creatures like Lucy (Australopithecus afarensis) who had brains like other apes. However, it now appears that based on this definition human history must reach back to the Miocene of 21 million years ago.''
Avon to 1974