(01) Ardipithecus ramidus | The Smithsonian · 2018. 9. 4. · Analysis of the skeleton reveals that humans did not evolve from knuckle-walking apes, ... reclassi/ed in 1995 because

(01) Ardipithecus ramidus | The SmithsonianInstitution's Human Origins Program

Ardipithecus ramidus

Nickname: Nickname: Ardi

Where Lived: Where Lived: Eastern Africa (Middle Awashand Gona, Ethiopia)

When Lived: When Lived: About 4.4 million years ago

Ardipithecus ramidus was rst reported in 1994;in 2009, scientists announced a partial skeleton,nicknamed ‘Ardi’. The foot bones in thisskeleton indicate a divergent large toe combinedwith a rigid foot – it's still unclear what thismeans concerning bipedal behavior. The pelvis,reconstructed from a crushed specimen, is said to

show adaptations that combine tree-climbing and bipedal activity. The discoverersargue that the ‘Ardi’ skeleton re ects a human-African ape common ancestor that was notchimpanzee-like. A good sample of canine teeth of this species indicates very littledifference in size between males and females in this species.

Ardi’s fossils were found alongside faunal remains indicating she lived in a woodedenvironment. This contradicts the open savanna theory for the origin of bipedalism,which states that humans learned to walk upright as climates became drierand environments became more open and grassy.

Year of Discovery: Year of Discovery: 1994

http://humanorigins.si.edu/evidence/human-fossils/species/ardipithecus-ramidus



History of Discovery: History of Discovery: A team led by American paleoanthropologist Tim White discovered the rst Ardipithecusramidus fossils in the Middle Awash area of Ethiopia between 1992 and 1994. Since thattime, White’s team have uncovered over 100 fossil specimens of Ar. ramidus . White andhis colleagues gave their discovery the name Ardipithecus ramidus (‘ramid’ means ‘root’ inthe Afar language of Ethiopia and refers to the closeness of this new species to the roots ofhumanity, while ‘Ardi’ means ‘ground’ or ‘ oor’). At the time of this discovery, the genusAustralopithecus was scienti cally well established, so White devised the genus nameArdipithecus to distinguish this new genus from Australopithecus. In 2009, scientistsformally announced and published the ndings of a partial skeleton (ARA-VP-6/500),nicknamed "Ardi", first found in 1994.

Height: Height: Females: average 3 ft 11 inches (120 centimeters)We don’t know everything about our early ancestors—but we keep learning more!Paleoanthropologists are constantly in the field, excavating new areas with groundbreakingtechnology, and continually filling in some of the gaps about our understanding of humanevolution.

Weight: Weight: Females: average 110 lbs (50 kg)

Below are some of the still unanswered questions about Ardipithecus ramidus that may beanswered with future discoveries:

1. Does the pelvis of Ar. ramidus support the hypothesis that this early humanspecies was bipedal? The pelvis was reconstructed from crushed fossils and, accordingto some scientists, is only suggestive of bipedalism.

2. What is the average size of male Ar. ramidus individuals? If more fossils support theoriginal nding of relatively low sexual dimorphism, how does this relate to male andfemale size di erences in other early humans at the base of our family tree -- and whatdoes it mean?




How They Survived: How They Survived: Ardipithecus ramidus individuals were most likely omnivores, which means they enjoyedmore generalized diet of both plants, meat, and fruit. Ar. ramidus did not seem to eat hard,abrasive foods like nuts and tubers.

How do we know they were omnivores?How do we know they were omnivores?The enamel on Ar. ramidus teeth remains show it was neither very thick nor very thin. Ifthe enamel was thick, it would mean Ar. ramidus ate tough, abrasive foods. If the enamelwas thin, this would suggest Ar. ramidus ate softer foods such as fruit. Instead, A. ramidushas an enamel thickness between a chimpanzee’s and later Australopithecus or Homospecies, suggesting a mixed diet. However, the wear pattern and incisor sizes indicate Ar.ramidus was not a specialized frugivore (fruit-eater). Ar. ramidus probably also avoidedtough foods, as they did not have the heavy chewing specializations of laterAustralopithecus species.

Evolutionary Tree Information: Evolutionary Tree Information: Over 100 specimens of Ardipithecus ramidus have been recovered in Ethiopia. Eventhough it has some ape-like features (as do many other early human species), it also has keyhuman features including smaller diamond-shaped canines and some evidence of uprightwalking. It may have descended from an earlier species of Ardipithecus that has been foundin the same area of Ethiopia, Ardipithecus kadabba.



(02) Ardipithecus ramidus - Australian Museum

Discovered in the 1990s, this is one of the earliestof our hominin ancestors yet discovered.

Background of discovery - Age - 4.4 to 4.2 million years ago

Important fossil discoveriesImportant fossil discoveries

Hundreds of pieces of fossilised bone wererecovered during 1992-1994, all from localitieswest of the Awash River, in Aramis, Ethiopia.The nds number over 110 specimens andrepresent about 35 individual members of thisspecies. Most of the remains are dental, but someskull and limb bones were also found. A partialhumerus (arm bone) indicates that this specieswas smaller than the average Australopithecusafarensis.

In 2005, the remains of 9 individuals were recovered from As Duma in northern Ethiopia.The remains mostly consist of teeth and jaw fragments, but also some bones from thehands and feet.

Some specimens discovered earlier in Kanapoi, Lothagam and Tabarin could also belongto this species.

Key specimensKey specimens

ARA-VP-6/1 teeth: This is the holotype for this species. It consists of teeth and jawbone and was found in Aramis in 1993.

https://australianmuseum.net.au/ardipithecus-ramidus



'Ardi' ARA-VP-6/500: A partial skeleton found in 1994, consisting of about 125pieces, was described and published in 2009. It is the oldest known skeleton of ahuman ancestor. The individual is believed to be a female and is nicknamed ‘Ardi’.She weighed about 50kg and stood about 120cm tall. The skeleton was in extremelypoor condition and it took the team 15 years to excavate, scan, make virtualreconstructions, assemble and then analyse. The results were hugely signi cant interms of how we view the evolution of the earliest hominins and the physicalappearance of the last common ancestor of humans and chimpanzees. The skeletondoes not look much like a chimp or gorilla or have the expected 'transitional'features. Instead, it may well preserve some of the characteristics of the last chimp-human ancestor.

Analysis of the skeleton reveals that humans did not evolve from knuckle-walkingapes, as was long believed. It also indicates that chimpanzee evolution underwenthigh degrees of specialisation since diverging from the last common ancestor and thusthese apes are poor models for understanding the appearance of this ancestor.

What the name meansWhat the name means

The name is derived from the local Afar language. ‘Ardi’ means ‘ground’ or ‘ oor’ and‘pithecus’ is Latinised Greek for ‘ape’. The name ‘ramid’ means ‘root’ in the Afar language.

DistributionDistribution

Fossils belonging to this species were found in eastern Africa in the Middle Awash valley,Ethiopia. Additional fossils that may also belong to this species have been collected innorthern Kenya.

Relationships with other speciesRelationships with other speciesThis species position as a direct ancestor of humans is unclear and scientists are stilldebating where it should be placed relative to our direct line. The discovers think it wasancestral to Australopithecus - it is the only putative hominin in evidence between 5.8 and4.4 million years ago - but others do not agree. Even if Ardipithecus ramidus is not on ourdirect line, it must have been closely related to the direct ancestor and probably similar inappearance and adaptation. It also o ers new insights into how we evolved from thecommon ancestor we share with chimps.




This species was originally classi ed as Australopithecus ramidu s in 1994, but wasreclassi ed in 1995 because its discoverers believed it was distinct enough to be placed intoa new genus, Ardipithecus.

Key physical featuresKey physical featuresThis species was a facultative biped and stood upright on the ground but could move on allfour limbs in trees. Features of the anatomy are extremely primitive.

Brain - Brain - about 300-350cc, similar in size to modern female chimpanzees and bonobos

Body size and shapeBody size and shape

similar in size to modern chimpanzees. The most complete specimen, a female, stoodabout 120cm tall males were only slightly larger than females the body shape was more ape-like than humans, but di ered from living African apesin a number of significant features

LimbsLimbs

mix of primitive and derived features suggest this species was able to walk upright onthe ground yet efficiently climb trees long powerful arms that were not used for weight-bearing or knuckle-walking as withquadrupedal apes bones in the wrist (particularly the midcarpal joint) provided exibility and the palmbones were short. These features suggest this species was not a knuckle-walker andthat the palms could support the body weight when moving along branches




finger bones were long and curving, both features useful for grasping branches upper and lower legs bones (femur and tibia) have features consistent with bipedalism feet were relatively at and lacked arches, indicating this species could probably notwalk or run long distances

they had grasping abducted toe characteristic of gorillas and chimps List item #2 the foot was more rigid than chimpanzees with the bases of the four toe bonesoriented to reinforce the forefoot when pushing o . Chimps have a highly exiblemidfoot that improves their ability to grasp and climb but are less e ective forpropulsion when walking on ground

PelvisPelvis

has a mix of features useful for both climbing and upright walking and suggests thespecies still spent significant time in the trees shape of the upper blades (ilium) appear short and broad like Australopithecusafarensis, indicating that the gluteal muscles had been repositioned. This lowered thebody's centre of mass so to balance on one leg when walking the lower pelvis is large and the angle of the ischial surface does not face upward as itdoes in humans and Australopithecus. These are primitive features that suggest thisspecies had massive hindlimb muscles for climbing and did not walk like A. afarensis

the sciatic knotch is similar in size and shape to later hominins. This is a derivedfeature and is not found in chimpanzees

Jaws and teethJaws and teeth

much of the dentition is ape-like including relatively large canines and molars tooth enamel thickness is intermediate between that of chimpanzees andAustralopithecus canines are less projecting and smaller than those of all other known apes and there isno evidence of honing. The base of the canines in both sexes are similar in size tofemale chimpanzees and male bonobos, but have shorter crown heights




upper canines are shaped like diamonds, rather than the pointed shape seen in Africanapes, whch is a derived feature shared with Australopithecus afarensis . Lower caninesappear to have less derived features. the jaw displayed signi cant forward projection compared to humans, but less thanmodern African apes pre-molars have derived features that are more advanced in the human direction

canines (non-sharpened and small) and other teeth share features with Orrorintugenensis

SkullSkull

skull rests atop the spinal column, indicating this species was bipedal, although itprobably walked in a slightly different manner than humans the cranial base is short from front to back, indicating the head balanced on top of thespine the face is small and in a more vertical position than chimpanzees

the ridge above the eye socket is unlike that of a chimpanzee

LifestyleLifestyleCultureCulture

There is no evidence for any speci c cultural attributes, but they may have used simpletools similar to those used by modern chimpanzees, including:

twigs, sticks and other plant materials that were easily shaped or modi ed. These mayhave been used for a variety of simple tasks including obtaining food. unmodi ed stones, that is stones that were not shaped or altered before being used.These tools may have been used to process hard foods such as nuts.

Environment and dietEnvironment and diet

Associated animal and plant fossils indicate this species lived a in relatively moist andheavily forested woodland. Fossil species include plants such as fig, palm and hackberry andanimals like colobine and baboon-like monkeys, kudu, peafowl, bats, shrews, rodents,doves, eagles, owls and parrots.




The species, with its ape-like feet, probably spent considerable time in the trees looking forfood and shelter.

Diet may have included nuts, fruit, leaves, tubers, insects and small mammals. They wereprobably more omnivorous than chimps (based on the size, shape and enamel of theteeth), and fed both in trees and on the ground. The evidence is inconclusive, but studiessuggest the front teeth were regularly used for clamping and pulling, possibly re ecting adiet that included large amounts of leaves. Tooth enamel analysis suggests they ate fruit,nuts and leaves. Carbon-isotope studies of teeth show they ate woodland rather thangrassland plants.

Fran Dorey , Exhibition Project Coordinator Last Updated: 26 October 2015


https://australianmuseum.net.au/staff/fran-dorey

http://www.becominghuman.org/node/ardipithecus-ramidus-essay

(03) Ardipithecus ramidus essay | Becoming Human

Ardipithecus ramidus

Ardipithecus ramidus is a hominin species datingto between 4.5 and 4.2 million years ago (mya)using paleomagnetic and radioisotopic datingmethods. (Paleomagnetic uses periodic reversalsin the Earth’s magnetic eld; radioisotopicutilizes the known rate of decay of oneradioisotope into another) Importantly, Ar.ramidus represents the oldest species thatpossesses features unequivocally linked to thehominin lineage. Thus, Ar. ramidus is the bestevidence discovered thus far for the root of thehominin family tree. Fossils of this species, foundin the Middle Awash region and the site of Gonain Ethiopia, possess derived features (featuresdi erent from those found in the ancestor) in theskull and teeth. The postcranial skeleton of Ar.ramidus, however, suggests this species had not

evolved obligate bipedality ("obligate" means the skeletal anatomy limits locomotion toone means, in this case bipedality. Obligate is the oppodite of functional bibedality,possessed by Chimpanzees - Pan troglodytes - for example, who can walk upright for shortdistances or climb in trees). This combination of traits is important because scientists havelong considered obligate bipedality to be a de ning characteristic of the hominin lineage. The traits possessed by Ar. ramidus, however, demonstrate that hominin-like skulls andteeth evolved before obligate bipedality and suggest the earliest hominins were not obligatebipeds.

The skull of Ar. ramidus is represented by most of the cranial vault (the part of the skullthat covers the brain), parts of the cranial base (the part of the skull below the brain, inwhich the brain sits), and most of the right half of the face. The features of the skull link thisspecies to other hominin species, but also suggest primitive similarities shared with




living apes. For example, the skull is small relative to later hominins (the cranial capacity is300 to 350 cubic centimeters, about the size seen in female chimpanzees and bonobos[pygmy chimpanzees]). Like apes and other early hominins, Ar. ramidus exhibitssubstantial prognathism (forward projection) of the face. Unlike apes, however, Ar.ramidus does not exhibit prognathism below the nasal aperture. The posterior (towardsthe back) portion of the cranial base is shorter than in chimpanzees, a trait also seen in otherhominins. It should be noted that these two traits (i.e., lack of prognathism in the lowerpart of the face and a short cranial base) are also found in Sahelanthropus tchadensis, anearlier, purportedly hominin species.

The dentition of Ar. ramidus is well represented, including all types of teeth (incisors,canines, premolars and molars) and associated upper and lower teeth. In general, theabsolute and relative sizes of the teeth (excluding the canines) are roughly similar to thoseof chimpanzees, but the incisors are smaller and the second and third molars are larger thani n Pan. The thickness of the dental enamel in Ar. ramidus is intermediate betweenchimpanzees and other hominin species; speci cally, dental enamel is thinner than inchimpanzees but thicker than in other hominin species. The canine teeth of Ar. ramidusshow derived hominin features. Most notably they are substantially reduced relative tothat seen in living apes. In addition, Ar. ramidus lacks the canine honing complexwhereby the upper canine is sharpened on the anterior surface of the lower premolar, afeature found in all living apes and no hominin species. Ar. ramidus retains a diastema(gap) between the incisors and canines, which is seen in apes and variably in Au. afarensis;however, this diastema is much smaller than that seen in apes and more like that found inAu. afarensis.

The Ar. ramidus forelimb is known from several specimens including one nearly completeforelimb fossil. Fossils of the Ar. ramidus humerus (the bone in the upper arm) closelyresemble humeri of other hominin species, including an elliptically-shaped humeral head(the part of the humerus that connects to the shoulder blade to form the shoulder joint)and a shallow groove for the long head of the biceps brachii muscle. In these ways, thehumerus of Ar. ramidus also differs from those of living apes. Fragmentary radii and ulnae




(lower arm bones; ‘radii’ is the plural of ‘radius.’ the bone on the outside of the lower arm;‘ulnae’ is the plural of ‘ulna,’ the bone on the inside of the lower arm ) are also representedand possess features not exhibited by living African apes. For example, the part of the ulnathat connects with the humerus faces forward, unlike that of African apes, which facesupward. In addition, the metacarpals (hand bones) are di erent from those of the livingapes in that they lack prominent ridges and grooves where the hand bones connect to thebones of the wrist. The Ar. ramidus hand phalanges ( nger bones), by contrast, are longerthan those of other hominins, being intermediate in length between chimpanzees andgorillas—i.e., the Ar. ramidus hand phalanges are shorter than those of chimpanzees, butlonger than those of gorillas

The Ar. ramidus hindlimb is represented by a partial, but damaged, pelvis, two partialfemora (thigh bones), and most of the foot. Unlike apes, the Ar. ramidus ilium (the upper,fan-shaped bone of the pelvis) is ared out to the side of the body. In this way, the pelvis isof this species is like all other hominin pelves (plural of pelvis). The aring of the iliumshifts the gluteal muscles more to the outside of the body, which, in turn allows weight tobe borne on one foot during bipedal walking. Interestingly, in contrast to its hominin-likeilium, the Ar. ramidus ischium (lower bone of the pelvis) more closely resembles those ofthe African apes. In particular, the shape and size of the ischium in Ar. ramidus suggeststhe hamstring muscles were strongly developed. Remains of the foot demonstrate that,unlike all known hominin species, Ar. ramidus had an opposable big toe (a big toe that,like those of living apes, is mobile like a human thumb). In addition, like later, obligatelybipedal hominins, the four other toes of Ar. ramidus are at and rigid. It should bementioned, however, that in this way the foot of Ar. ramidus is also similar to manyextinct apes and living monkeys. The foot phalanges (toe bones) of this species areintermediate in length between chimpanzees and species in the genus Homo.

The extensive fossil record of Ar. ramidus permits reconstruction of the behavior of thisspecies. For instance, the dental remains suggest the Ar. ramidus’ diet constituted tougherfoods than those of later hominins but less tough than those of chimpanzees. The relatively




small incisors and large molars may indicate Ar. ramidus relied less on ripe fruit thanchimpanzees. Furthermore, dental wear indicates Ar. ramidus likely had a less abrasivediet than did the later Au. afarensis. The small size of the canines (relative to living apes)suggests male-male competition using canines in ghting or threat displays was lessimportant in Ar. ramidus (and all later hominins) than in other primate species.

The locomotor behavior (behavior involved with traveling from place to place) of Ar.ramidus can also be reconstructed. In particular, scientists argue that the forelimb of Ar.ramidus lacks the specializations related to suspensory locomotion (moving around whilesuspended below branches) and knuckle-walking. In particular, these researchers argue Ar. ramidus lacked the sti ness of the wrist (which facilitates knuckle walking) that isexhibited by knuckle-walking apes. Instead, these researchers suggest that the Ar. ramiduswrist was mobile (like that on living monkeys). The shape and size of the ischium suggestthat the hamstring muscles were well-developed, a condition seen in living primates thatemphasize climbing in their locomotor behaviors. Based on these observations, researchersargue that Ar. ramidus emphasized climbing and spent most of its time walking on all fourlimbs above branches.

The evolutionary relationships between Ar. ramidus and other hominin species are ofgreat interest to paleoanthropologists. An older hominin taxon, Ardipithecus kadabba,which is also found in the Middle Awash of Ethiopia, is argued by some researchers to be adirect ancestor of Ar. ramidus because both species share many features, such as thin dentalenamel and larger canines. Furthermore, some researchers argue Ar. ramidus is on a singleline of descent in eastern Africa, beginning with Ar. kadabba to Ar. ramidus toAustralopithecus anamensis and ending with Au. afarensis. This hypothesis, however,would imply that a large amount of morphological change would have had to occurbetween Ar. ramidus and Au. anamensis in a very short period of time (approximately 200thousand years). Many scientists do not believe this amount of morphological changecould occur in a single lineage in such a short time. Paleoanthropologists are also interested




in Ar. ramidus because at 4.4 mya, it provides the first extensive fossil evidence that extendsour understanding of the last common ancestor we shared with chimpanzees. Scientistsargue that the morphology of Ar. ramidus demonstrates that great ape adaptations forforelimb suspension and knuckle-walking were not present in the last common ancestor ofhominins. This argument also implies that living great apes evolved suspensoryadaptations separately and that none is a good model of the anatomy and behavior of thelast common ancestor of chimpanzees and humans.

The two sites from which Ar. ramidus fossils have been recovered (i.e., Middle Awash andGona) o er slightly di erent habitat reconstructions. At Gona, many large mammalfauna associated with Ar. ramidus are intense grazers, which would indicate a habitat witha signi cant grassy component. Other indicators from Gona, however, suggest that theenvironment was a more mosaic habitat, consisting of closed woodlands and more open,grassy environments. Similar evidence from the parts of the Middle Awash region whereAr. ramidus has been found, in contrast, lead to reconstructions of a closed woodland.Although the Aramis reconstruction suggests a more closed environment, both habitatreconstructions are consistent with idea that bipedality initially evolved in a woodlandenvironment rather than in a more open savanna grassland.


https://www.scientificamerican.com/article/ardi-hominid-human-ancestor/

Credit: J.H. MATTERNESBy Katherine Harmon, 1 October, 2009

10/01/200110/01/2001 The rst full analysis of a 4.4-million-year-old early human paints a clearerpicture of what the last common ancestor of humans and chimpanzees may have lookedlike, which is not, after all, that much like a chimp at all. The ancient Ardipithecus ramidus("Ardi", as the most complete female specimen is known) is described in 11 research paperspublished online today in Science. The prodigious research e ort combines Ardi's fossilswith those from many other Ar. ramidus individuals—both male and female—found nearthe Awash River in the Afar Rift region of Ethiopia.

Ar. ramidus, although likely millions of years more recent than the so-called missing linkbetween chimpanzees and humans, represents "coming as close as we've ever come to thatlast common ancestor," Tim White of the University of California, Berkeley, one of thestudies' lead authors, said in a recorded interview for Science.

Ardi is, in fact, "so rife with anatomical surprises, that no one could have imagined itwithout direct fossil evidence," wrote C. Owen Lovejoy, a professor of anthropology atKent State University in Ohio, and his colleagues in a summary of one of the papers.


(05) Long-Awaited Research on a 4.4-Million-Year-Old Hominid Sheds New Light on Last Common Ancestor

!"#$ %& %' ()* +, -./.00. 1*./%'2,

3%4(**' 5*.1& %' ()* 6.7%'28 . /9&&%*1 94 :.:*1& 9' ; +1/%; :<0=%&)*/ %' >?%*'?* &<22*&( ().( =%7* )<6.'&8 ? )%6:.'@**& ).A* <'/*129'* &<0&(.'(%.= *A9=<(%9'.15 ? ).'2*


Among the surprises: Ardi's jaw and limbs show she was a forest-dwelling omnivore, not afruit-eater like today's chimps or an open savanna–dweller like other early hominids. Ardihad a brain about the size of a modern chimp's relative to body size (about a third the sizeof a modern human's). And Ar. ramidus's foot is strikingly unlike that of a modernchimpanzee, the authors of another paper (led by Lovejoy) explain.

For a primitive cousin who likely stood at only about 120 centimeters and weighed about50 kilograms, Ardi is likely to make a big impact in the eld of paleoanthropology. Forinstance, Ardi's physical form also has implications for many other ancient animals,including the controversial six-million- to seven-million-year-old Sahelanthropustchadensis, discovered in Chad in 2001. The similarities in skull size and shape among thesetwo species now has prompted the researchers of one of the new papers (led by Gen Suwa,a professor at the University of Tokyo) to conclude that S. tchadensis was, indeed, an earlyhominid, rather than a female ape as others have suggested.

Fragile fossilsFragile fossils

First announced 15 years ago with only scant tooth and jaw fragments, Ar. ramidus hadremained a relative paleoanthropological secret amidst growing literature on other earlyhominids, such as the well-known Lucy, a 3.2-million-year-old Australopithecus afarensis.

For the new papers, an international team of researchers assembled and described the morethan 110 pieces of Ardi's skeleton, including portions of the skull, hands, feet, arms, legsand pelvis, and those of other Ar. ramidus specimens and surrounding plants and animals.

"It's an amazing amount of material," says Carol Ward, an associate professor andintegrative anatomy specialist at the University of Missouri–Columbia (M.U.). "That initself is astonishing."


!"#$ %&'()*+,-./0 1/2/,345 &' , 676)8-99-&'):/,3);90 <&=-'-0 >5/02 ?/+ %-(5. &' %,2. @&==&' *'4/2.&3


The recovery e orts themselves took some "heroic e orts," says Brian Richmond, ofGeorge Washington University's Center for the Advanced Study of HominidPaleobiology (CASHP), in Washington, D.C. Poorly fossilized, many of the bones wouldcrumble with a normal human touch, so they were carefully removed, cast and scanned.

Long before the fossils were unearthed, they sustained quite a bit of damage, leaving theskull and the pelvis crushed and distorted. Close study and computer modeling helpedresearchers put the pieces back together, but, Richmond notes, "it takes a substantialamount of reconstruction," and a bit of guesswork to assemble the body—and movements—of a creature long extinct.

By hand or by footBy hand or by foot

Perhaps one of the biggest questions that remains in the eld of human evolution is howthe modern two-legged gait came to be, and Ardi complicates some common assumptionsmade in the past by anthropologists.

Today's chimpanzees and gorillas get around on the ground by walking on the hind feetand the knuckles of their hands, leaving many to speculate that early humans may wellhave done the same. "It has long been assumed that our hands must have evolved fromhands like those of African apes," Lovejoy and his co-authors wrote in one paper summary.Other early specimens have lacked su cient hand bones to establish if they weretransitioning from knuckle walking, note the authors of one of the papers.

The more complete hands of Ardi, however, throw another wrench into this theory. Thesti but strong hands of modern great apes are well-adapted to navigating life in thetreetops. Humans, however, have weaker but more exible hands, allowing for betterdexterity and tool use. The hands of Ar. ramidus were indeed strong enough to hang fromtree branches but don't show any indication of knuckle-walking, and in some ways theymay have been more flexible than our own, Lovejoy and co-authors note.


!"#$ %&'()*+,-./0 1/2/,345 &' , 676)8-99-&'):/,3);90 <&=-'-0 >5/02 ?/+ %-(5. &' %,2. @&==&' *'4/2.&3


So does that mean that Ardi was walking on two legs? By the time Lucy came along about3.2 million years ago, her cadre was already fairly well-adapted to bipedal walking(although not quite so well as modern humans). The researchers suggest that Ardi was, infact, an upright walker and that "Ar. ramidus could walk without shifting its center of massfrom side to side," a hallmark of latter hominids, wrote Lovejoy and his colleagues.

M.U.'s Ward is not convinced that Ardi was quite as steady on her feet as the authorssuggest. After examining some of the gures, Ward notes that the specimen's knees mayactually have been spaced farther apart, making Ardi less able to ow from one foot toanother without making the large adjustment of body weight.

She is not alone in her skepticism. "There is precious little to indicate that it was an uprightwalker," Richmond says, which actually surprised him, noting that there is other evidenceof bipedality going back some four million years ago (work on fossils of Orrorin tugenensiseven suggests bipedality going back some six million years). He also cites the lack of a kneejoint as an unknown key to the species's locomotion capabilities.

Its hips do, however, appear to be moderately adjusted to accommodate some uprightwalking. But they were not as similar to modern human hips as those of Australopithecus.And the feet, although more primitive than a chimpanzee's, "certainly would have beencapable of bipedal walking," Richmond says, although the presence of a large grasping toeand other aspects make it less well-suited to getting around upright.

Perhaps more fossil evidence will help to clarify the path from the tree branch to thesavannah, but in the meantime, Ardi has brought some welcome new evidence to the eld,Ward notes. "The question is no longer, 'Why did our ancestors stand upright?'" she says."It's, 'Why did they never drop down on all fours when they came out of the trees?'"


!"#$ %&'()*+,-./0 1/2/,345 &' , 676)8-99-&'):/,3);90 <&=-'-0 >5/02 ?/+ %-(5. &' %,2. @&==&' *'4/2.&3


Forest dwellerForest dweller

Challenging long-held assumptions about where—and why—early humans droppeddown from the trees and stretched their legs, Ar. ramidus appears to have lived not in asavanna but in a forest.

Previous excavation of early humans has often been in areas in which ancient deluges hadmixed various biomes and layers together, providing a convoluted picture of eachindividual's original environment, U.C. Berkeley's White et al. wrote in one of the newpapers. Ethiopia's Afar Rift location, however, had experienced no such archaicamalgamation, providing paleoanthropologists with a clearer picture of Ardi's world.

Analysis of the area's geology and other nearby fossils revealed ancient g and hackberrytrees as well as new species of mammals and birds. These ndings, along with the dearth ofgrassland-dwelling species, such as the larger hoofed species found elsewhere, led theauthors of one of the papers (led by Giday WoldeGabriel, a geologist at Los AlamosNational Laboratory in New Mexico) to propose that the area "was humid and cooler thanit is today, containing habitats ranging from woodlands to forest patches," they wrote in asummary.

Given that they did inhabit a largely wooded area, however, means that ground-basedtravel was probably secondary, Ward says. "The most important way of getting around forthese animals was climbing trees." Nevertheless, it raises questions as to why these animalsmay have started perambulating upright before later hominids moved onto the grasslands,whereas ancestors of chimpanzees and other great apes eventually retreated deeper into theforest.

Social speculationsSocial speculations

What can the outlines of Ardi's frame reveal about the daily lives of this species?


!"#$ %&'()*+,-./0 1/2/,345 &' , 676)8-99-&'):/,3);90 <&=-'-0 >5/02 ?/+ %-(5. &' %,2. @&==&' *'4/2.&3


Researchers found an important indicator in the canine teeth from male Ar. ramidusspecimens. Modern male chimpanzees and gorillas have long, sharp canine teeth, whichthey use in ghts with other males to obtain female mates. Ar. ramidus—and to an evenlesser extent, humans—don't have such fearsome teeth. In the papers, Lovejoy suggeststhat this may be a sign of the absence of such male-to-male competition and aggression overfemale mates and perhaps an indication that the males were starting to be more involved inthe rearing process.

These ancient Ar. ramidus males also appear to have been nearly the same size of thefemales, another indication that they likely had a di erent social system than modernchimpanzees, whose aggression-based hierarchy had long been the foil for early hominids.

As White noted in his interview, the absence of these two key gender di erences seems tobe “signaling a new social structure.”

Others in the eld agree that these two signatures are likely indicators of a di erent type ofmating system than the one seen in modern African apes. However, recreating the detailsof a social system purely on fossil evidence is tricky, if not impossible, says Michael Plavcan,an associate professor of Anthropology at the University of Arkansas in Fayetteville. Somenew world monkeys, for example also show little sexual body size or canine toothdimorphism and pair o for life—“the family counsel’s animal of the year,” says Plavcan—others, with similar characteristics are, he explains, “intensely promiscuous.”

Next StepsNext Steps

Like any signi cant scienti c discovery, Ar. ramidus raises more questions than it answers."It's going to keep generations of students busy," CASHP's Richmond says of the research.It will also likely usher in a change in the common understanding that modern humansdescended directly from chimpanzees—as popularized by the illustrated "quadrupedal


!"#$ %&'()*+,-./0 1/2/,345 &' , 676)8-99-&'):/,3);90 <&=-'-0 >5/02 ?/+ %-(5. &' %,2. @&==&' *'4/2.&3


monkey to upright man" sequence. Accepting the new view of human evolution that theArdi analyses suggest, says Ward, will mean "tearing that [depiction] up and throwing itout the window."

This new evidence calls into question many assumptions that have been made aboutHomo sapiens's assumed privileged evolution. Indeed, if anything, Ardi reveals thatchimpanzees, too, have been on quite an evolutionary odyssey in the past seven million to10 million years.

It also points the way toward more work outside of Ardi's clan. "This just highlights theneed for more research to nd the last common ancestor of chimpanzees and humans,"Richmond says. "Ultimately we want to know where we rst came from and what werethe factors that let us take our unique steps toward humanity," he says. But the fossil recordwill have to be the nal arbitrator. "I think at this point it's premature to make conclusionsabout the common ancestor without having evidence," he says.

Indeed, even White noted that it is still too early to say for sure exactly how theseevolutionary lines are related and how the hominids came to start walking upright.

The analysis of Ardi gives new poignancy to the notion, set forth nearly 150 years ago byCharles Darwin and Thomas Huxley, that there was likely a common ancestor quitedi erent from both modern humans and great apes. Darwin knew, White noted in therecorded interview that, "the only way we're really going to know what this last commonancestor looked like is to go and find it."


!"#$ %&'()*+,-./0 1/2/,345 &' , 676)8-99-&'):/,3);90 <&=-'-0 >5/02 ?/+ %-(5. &' %,2. @&==&' *'4/2.&3

http://content.time.com/time/magazine/article/0,9171,1927289,00.html

T. White

Science magazine with the skeleton ofArdipithecus ramidus, aka "Ardi."

The path of just such a discovery began in November 1994 with the unearthing of twopieces of bone from the palm of a hominid hand in the dusty Middle Awash region ofEthiopia. Within weeks, more than 100 additional bone fragments were found during anintensive search-and-reconstruction e ort that would go on for the next 15 years andculminate in a key piece of evolutionary evidence revealed this week: the 4.4 million–year–old skeleton of a likely human ancestor known as Ardipithecus ramidus (abbreviatedAr. ramidus).

In a series of studies published in the Oct. 2 special issue of Science — 11 papers by a totalof 47 authors from 10 countries — researchers unveiled Ardi, a 125-piece hominidskeleton that is 1.2 million years older than the celebrated Lucy (Australopithecusafarensis) and by


(06) Ardi Fossil Discovery: New Human-Evolution Puzzle Piece

!"#"!#$""% &'()*'+( ,)- -./ 0-,*1 ,2 .)34+

,*'('+0 '0 5'6/ 400/375'+( 4 .)(/8 9,3:5'94-/;

<'(04= :)>>5/ -.4- .40 5,0- 3,0- ,2 '-0 :'/9/0? @4+1 ='55 +/A/* 7/ 2,)+;8 4+; -.,0/ -.4- ;, -)*+ ): 4*/ 0,3/-'3/0 .4*; -, :549/? BA/*1 0, ,2-/+8 -.,)(.8 2,00'5 .)+-/*0 0-)375/ ):,+ 4 ;'09,A/*1 -.4- C550 '+ 4 7'( 9.)+6 ,2 -./ :)>>5/ 455 4- ,+9/ D 4+; 0'3)5-4+/,)051 */0.4:/0 -./ A/*1 :'9-)*/ -./1 -.,)(.- -./1 =/*/ 7)'5;'+(?


far the oldest one ever found. Tim White of the University of California, Berkeley, a co-leader of the Middle Awash research team that discovered and studied the new fossils, says,"To understand the biology, the parts you really want are the skull and teeth, the pelvis, thelimbs and the hands and the feet. And we have all of them."

That is the beauty of Ardi — good bones. The completeness of Ardi's remains, as well asthe more than 150,000 plant and animal fossils collected from surrounding sediments ofthe same time period, has generated an unprecedented amount of intelligence about oneof our earliest potential forebears. The skeleton allows scientists to compareArdipithecus directly with Lucy's genus, Australopithecus, its probable descendant.Perhaps most important, Ardi provides clues to what the last common ancestor shared byhumans and chimps might have looked like before their lineages diverged about 7 millionyears ago.

Ardi is the earliest and best-documented descendant of that common ancestor. But despitebeing "so close to the split," says White, the surprising thing is that she bears littleresemblance to chimpanzees, our closest living primate relatives. The elusive commonancestor's bones have never been found, but scientists, working from the evidenceavailable — especially analyses of Australopithecus and modern African apes — envisionedGreat-Great-Grandpa to have looked most nearly like a knuckle-walking, tree-swingingape. But "[Ardi is] not chimplike," according to White, which means that the last commonancestor probably wasn't either. "This skeleton ips our understanding of humanevolution," says Kent State University anthropologist C. Owen Lovejoy, a member of theMiddle Awash team. "It's clear that humans are not merely a slight modi cation of chimps,despite their genomic similarity."

So what does that mean? Based on Ardi's anatomy, it appears that chimpanzees mayactually have evolved more than humans — in the scienti c sense of having changed moreover the past 7 million years or so. That's not to say Ardi was more human-like thanchimplike. White describes her as an "interesting mosaic" with certain uniquely humancharacteristics: bipedalism, for one. Ardi stood 47 in. (120 cm) tall and weighed about110 lb. (50 kg), making her roughly twice as heavy as Lucy. The structure of Ardi's upper




pelvis, leg bones and feet indicates she walked upright on the ground, while still retainingthe ability to climb. Her foot had an opposable big toe for grasping tree limbs but lackedthe exibility that apes use to grab and scale tree trunks and vines ("Gorilla and chimp feetare almost like hands," says Lovejoy), nor did it have the arch that allowed Australopithecusand Homo to walk without lurching side to side. Ardi had a dexterous hand, moremaneuverable than a chimp's, that made her better at catching things on the ground andcarrying things while walking on two legs. Her wrist, hand and shoulder bones show thatshe wasn't a knuckle walker and didn't spend much time hanging or swinging ape-style intrees. Rather, she moved along branches using a primitive method of palm-walking typicalof extinct apes. "[Ardi is] a lovely Darwinian creature," says Penn Statepaleoanthropologist Alan Walker, who was not involved in the discovery. "It has featuresthat are intermediate between the last common ancestor and australopithecines."

Scientists know this because they've studied not only Ardi's fossils but also 110 otherremnants they uncovered, which belonged to at least 35 Ar. ramidus individuals.Combine those bones with the thousands of plant and animal fossils from the site and theyget a remarkably clear picture of the habitat Ardi roamed some 200,000 generations ago. Itwas a grassy woodland with patches of denser forest and freshwater springs. Colobusmonkeys chattered in the trees, while baboons, elephants, spiral-horned antelopes andhyenas roamed the terrain. Shrews, hares, porcupines and small carnivores scuttled in theunderbrush. There were an assortment of bats and at least 29 species of birds, includingpeacocks, doves, lovebirds, swifts and owls. Buried in the Ethiopian sediments werehackberry seeds, fossilized palm wood and traces of pollen from g trees, whose fruit theomnivorous Ar. ramidus undoubtedly ate.

This tableau demolishes one aspect of what had been conventional evolutionary wisdom.Paleoanthropologists once thought that what got our ancestors walking on two legs in the

rst place was a change in climate that transformed African forest into savanna. In such anenvironment, goes the reasoning, upright-standing primates would have had the advantageover knuckle walkers because they could see over tall grasses to nd food andavoid predators. The fact that Lucy's species sometimes lived in a more woodedenvironment began to undermine that theory. The fact that Ardi walked upright in a

http://content.time.com/time/magazine/article/0,9171,1927289-2,00.html


https://www.scientificamerican.com/article/how-humanlike-was-ardi/

similar environment many hundreds of thousands of years earlier makes it clear that theremust have been another reason.

No one knows what that reason was, but a theory about Ardi's social behavior may hold aclue. Lovejoy thinks Ar. ramidus had a social system found in no other primates excepthumans. Among gorillas and chimps, males viciously ght other males for the attention offemales. But among Ardipithecus, says Lovejoy, males may have abandoned suchcompetition, opting instead to pair-bond with females and stay together in order to reartheir o spring (though not necessarily monogamously or for life). The evidence of thisharmonious existence comes from, of all things, Ardipithecus' teeth: its canine teeth arerelatively stubby compared with the sharp, dagger-like upper fangs that male chimps andgorillas use to do battle. "The male canine tooth," says Lovejoy, "is no longer projecting orsharp. It's no longer weaponry."

That suggests that females mated preferentially with smaller-fanged males. In order forfemales to have had so much power, Lovejoy argues, Ar. ramidus must have developed asocial system in which males were cooperative. Males probably helped females, and theirown o spring, by foraging for and sharing food, for example — a change in behavior thatcould help explain why bipedality arose. Carrying food is di cult in the woods, after all, ifyou can't free up your forelimbs by walking erect.

Deducing such details of social behavior is, admittedly, speculative — and severalresearchers are quick to note that some of the authors' other major conclusions needfurther discussion as well. One problem is that some portions of Ardi's skeleton werefound crushed nearly to smithereens and needed extensive digital reconstruction. "Tim[White] showed me pictures of the pelvis in the ground, and it looked like an Irish stew,"says Walker. Indeed, looking at the evidence, di erent paleoanthropologists may havedi erent interpretations of how Ardi moved or what she reveals about the last commonancestor of humans and chimps.


!"#$ %&'( )*++(, -(+.*/0&12 304 56789:;/*,6<(*9 =6>>,0 =(0.0


But Science doesn't put out special issues very often, and the extraordinary number andvariety of fossils described in these new papers mean that scientists are arguing over realevidence, not the usual single tooth here or bit of foot bone there. "When we started ourwork [in the Middle Awash]," says White, "the human fossil record went back to about 3.7million years." Now scientists have a trove of information from an era some 700,000 yearscloser to the dawn of the human lineage. "This isn't just a skeleton," he says. "We've beenable to put together a fantastic, high-resolution snapshot of a period that was a blank." Thesearch for more pieces continues, but the outlines of the puzzle, at least, are coming intofocus.


!"#$ %&'( )*++(, -(+.*/0&12 304 56789:;/*,6<(*9 =6>>,0 =(0.0


For such a petite creature, the 1.2-meter-tall "Ardi"(Ardipithecus ramidus) has made big waves in thepaleoanthropology world. The momentous nd—announced 15 years ago and formally described inScience this October—has deepened academicdebates about when bipedalism evolved, what ourlast common ancestor with chimpanzees lookedlike, and how some ancient primates gave way tomodern humans.

"This is a fascinating fossil not matter what sideyou come down on," says William Jungers, aprofessor and chairman of the Department ofAnatomical Sciences at the Stony Brook UniversityMedical Center in Long Island, N.Y. The 11-paper Science analysis has, indeed, sharpened moredifferences than it has smoothed over.

The authors of the papers, including Tim White of the University of California, Berkeley,propose that Ardipithecus was "an e ective upright walker" and that it "resolves manyuncertainties about early human evolution, including the nature of the last commonancestor." But many others in the eld propose that some of these statements may beoverblown. In fact, Jungers says, "I think some of the things they said might have been foreffect."

So, does Ardi represent a true step toward humanity, or should she remain up in the sidebranches of the evolutionary tree? White and his fellow authors do not propose to have ade nitive answer, but through painstaking analysis of the fossil data and surroundings,they conclude in the overview paper that, "There are no apparent features su cientlyunique to warrant the exclusion of Ar. ramidus as being ancestral to Australopithecus,"thus

proposing she might indeed be an early hominin (the ever-changing nomenclatural groupthat usually includes living humans and our close extinct relatives, also referred to byWhite et al. as hominids—although the latter title now often includes the great apes, aswell)


!"#$ %&' %()*+,-./ 0*1 2345-26 7 89-/+:-;-9 3)/4-9*+


But piecing together how Ardipithecus ts into the evolutionary story of humanity mayprove even more difficult than reconstructing Ardi's fragmented and fragile bones, and theprocess has already turned out to be a contentious one.

Able biped?Able biped?

Because the traditional hallmark of an early human has been the adaptation for uprightwalking, much of the debate over Ardipithecus's status hinges on how her lower bodybones t together—in particular, the position of her damaged ilium, the winglike upperpelvis bone. Depending on how this bone is oriented, muscles around the hip joints workdi erently, explains David Begun, a professor in the Department of Anthropology at theUniversity of Toronto.

The summary in one of the Science papers, led by Owen Lovejoy of Kent State Universityin Ohio, argues that by Ardi's time, "the gluteal muscles had been repositioned so that Ar.ramidus could walk upright without shifting its center of mass from side to side" (unliketoday's lumbering great apes), but a di erent interpretation of the ilium could change allof that.Despite the numerous images and descriptions put forth by the researchers, others arereluctant to take the reconstructions without a grain of salt. Begun says: "Maybe the piecesdo t together nicely, but the reality is they start out with a very damaged specimen, andthey end up with something very similar to an australopithecine" (the group that includes"Lucy," the 3.2-million-year-old Australopithecus as well as a 2.7-million-year-oldParanthropus). "It's very di cult not to make them look like something you have in yourmind if there's any chance of play," he says. Jungers also notes the perils of reconstruction,which in a case like Ardi's "requires a lot of guesswork."As the upper pelvis appears like it could belong to an early human, the bottom part looksmore like a quadrupedal, nonhuman primate, says Jungers, who recently met with Whiteand examined photos of the bones. White asserts, however, that after working with thefossils himself, there is no way that they could belong to "an animal that wasn't oftenwalking on its hind legs," unless the data "were deliberately ignored, or if we had madethem up," he argues.


!"#$ %&' %()*+,-./ 0*1 2345-26 7 89-/+:-;-9 3)/4-9*+


Comfortable climberComfortable climber

Even if Ardi's reconstructed hips don't convince everyone, her feet could provide someimportant insights into the species's locomotion. In a summary to one of the Sciencepapers led by Lovejoy, the authors note that, "although the foot anatomy of Ar. ramidusshows that it was still climbing trees, on the ground it walked upright." Ardi's feet do pointto a comfort with life in the trees. Her big toe, which Jungers calls "remarkably primitive,"is quite divergent—even more so than the grasping digit in modern-day chimpanzees—which would help with climbing.

None of the known foot components, no matter how well adapted to climbing, precludeArdipithecus from walking upright on the ground. Jungers, however, thinks "it reallydoesn't show any adaptations for bipedalism at all." In fact, he says, many components ofAr. ramidus don't make Ardi look that much more adept at walking upright thanchimpanzees—a primate that White et al. disavow as a model for early human evolution.In a summary paper led by Lovejoy, the authors describe Ardipithecus as a "facultativeupright walker," one that can walk on two legs if needed (to carry something in theforearms, for example) but that isn't necessarily prone to do so.

"What's ironic is that that's how you would describe bipedality in chimpanzees," Jungerssays—"they're facultative bipeds." Homo erectus, on the other hand, which lived about 2.6million years after Ardi, were obligate bipeds, and he points out, "even humans arefacultative climbers."

No matter how some of Ardi's bones are assembled or reassembled, the debate about howthe species got around on the ground may not be settled by further analysis of thisspecimen. Even though hundreds of bones were uncovered, the species still lacks a kneejoint. "I think a knee joint would seal the deal one way or another," Begun says. And morefoot bones wouldn't hurt either, Jungers notes.


!"#$ %&' %()*+,-./ 0*1 2345-26 7 89-/+:-;-9 3)/4-9*+


Cranial cluesCranial clues

Rather than continue the lineage debate below the belt, Ardi's most important featuresmight rest above her shoulders, Jungers says. "We have to abandon bipedality as thehallmark of being a 'hominin' sensu stricto if we hope to keep Ardi in our clade," he wrotein an e-mail to ScientificAmerican.com

"If we had just found the fossils below the neck, it's possible we wouldn't be talking aboutArdi as a hominin at all," he says.

The numerous cranial pieces that the research team uncovered might, however, help swaythe debate toward the early human camp. In a conversation with White, Jungers says, hewas compelled by the dental evidence—especially the upper canine teeth, which weresmaller and more humanlike than those of chimpanzees—to consider Ardi as an early stepin human evolution. The small canines and minimal size di erence between males andfemales of the species are "indicative of minimal social aggression," the authors of one ofthe Science summaries (led by White) wrote. If males didn't compete for females throughphysical aggression, co-author Lovejoy has argued, they might have been more involved inraising offspring—a key component of later human evolution.

The skull itself also raises questions about how similar Ardi was to our other ancestors,such as Lucy. The authors of the Science papers make note of the smaller lower face inArdipithecus, which doesn't project as much as a chimpanzee's and is shaped more like thato f Australopithecus. But outside researchers focus on the similarity in size to othernonhuman primates, such as extinct Miocene epoch apes.

White, however, prefers to take the specimen in full, calling pointedly piecemeal analysis"entirely hypothetical, and actually unrealistic." He grants that "if only an intermediatehand phalanx had been found, then it would not have been possible to ascertain thephylogenetic relationships of the species," but he concludes that, "the characters of the


!"#$ %&' %()*+,-./ 0*1 2345-26 7 89-/+:-;-9 3)/4-9*+

http://content.time.com/time/health/article/0,8599,1992115,00.html

dentition, skull and postcranial skeleton…are all uniquely shared by Ar. ramidus and laterhominids, to the exclusion of all other extant and extinct apes," he wrote in an e-mail."Even without the cranium and dentition," he maintains, "the same case would still besupported because of the shared derived traits in the hip and the foot."

He and his collaborators do not insist on upright walking as the only indicator that Ardiand her clade were indeed early humans, but he notes that so far it is part of the picture. Hesays that although their group's de nition of the family "Hominidae" was "not based onbipedality, per se," the designation "appears consistent with both bipedality and SCC[sectorial canine complex] loss happening close to the time of divergence" of the humanand chimpanzee lines.

A place in the evolutionary treesA place in the evolutionary trees

Long an evolutionary mystery, the last common ancestor shared by humans andchimpanzees may be at least partially clari ed by the discovery of Ar. ramidus, argued theauthors of the 600-plus pages of material submitted to Science about the species.

Begun and others are perhaps slower to propose a place for Ardi in the direct human linethan are the project researchers, who note that even though the species is "substantiallymore primitive than Australopithecus" (as they wrote in a summary led by White), "itappears…to have occupied the basal adaptive plateau of hominid natural history" (asanother summary, led by Lovejoy, noted).

But as di cult as it has been to claim Ardi as a close relative, it has also been di cult todismiss her. "I don't think its unfair to say that Ardi's precise phylogenic position is unclearand debatable at this time," Jungers comments. Even White notes that "the three mostlikely possibilities" are that Ardipithecus is either in the human line, chimpanzee line orpredates

both. "We assign it to the hominid [aka hominin] clade based on a series of newly evolvedcharacters that it shares exclusively with all other members of that clade—Australopithecusspecies and Homo sapiens," he says.


!"#$ %&' %()*+,-./ 0*1 2345-26 7 89-/+:-;-9 3)/4-9*+


From studying the published data in Science, Begun found "very little in the anatomy ofthis specimen that leads directly to Australopithecus, then to Homo sapiens," he says. "Thiscould very easily be a side branch."

Broader analyses of Ardi's place in the primate family tree and her role in the move toupright walking may have to wait until the original fossils and their casts become availablefor other researchers to examine. "We're raring to go to see how Ardi ts in," Jungers says.White himself seems anxious to let others see for themselves the evidence that he iscon dent in: "We welcome these investigators to have a close comparative look at thefossils before drawing conclusions on something as important as bipedality."

Opportunities to have a close look at the originals are being granted on a case-by-case basis.A more complete analysis of the nd is forthcoming in publications on the larger MiddleAwash Project (to be published by the University of California Press).*

Regardless of the eagerness to lay eyes on Ardi and the other specimens as well as lingeringquestions about the species's status as a hominin, most researchers applaud the signi cantwork involved in excavating and analyzing the fossils. "What those guys did was prettyamazing," Jungers says. The extensive documentation of Ar. ramidus' context has "set anew standard," which, he says, is "truly extraordinary."

*Correction (11/19/09): This paragraph was changed after publication to re ect thecurrent Middle Awash Project policies for viewing.


!"#$ %&' %()*+,-./ 0*1 2345-26 7 89-/+:-;-9 3)/4-9*+

http://middleawash.berkeley.edu/middle_awash.php


A reconstructed frontal view of Ardi

05/27/2010 05/27/2010 At a little over 4 ft. tall, she wassmall by human standards. But when Ardi, the4.4 million-year-old hominid fossil found inEthiopia in 1992, was nally introduced to theworld last October in a series of 11 audaciousstudies in the journal Science, she caused big

waves in evolutionary circles. Both TIME and Science named her the "Scienti cBreakthrough of the Year." But now Ardi has found herself in a spot of controversy. Twonew articles being published by Science question some of the major conclusions of Ardi'sresearchers, including whether this small, strange-looking creature is even a humanancestor at all.

Neither article challenges the veracity of the evidence published by the team of scientists,led by paleoanthropologist Tim White of the University of California, Berkeley, whichpainstakingly pieced Ardi together from more than 100 crushed fossil fragments. But theydo dispute the conclusions White and his colleagues reached from that evidence.

In the rst article, titled "Comment on the Paleobiology and Classi cation of Ardipithecusramidus," Esteban Sarmiento, a primatologist at the Human Evolution Foundation,argues that many of the "characters" — the scienti c term for physical traits — used byWhite to place Ardi on the human lineage are also shared by other primates. He argues thatthe


!"#$ %&'() *+(,-.(/./ 01233,-4, 5672- %-+,/.8& 08--,+.(8-


evidence suggests Ardi belongs to a species that evolved before the moment when humans,apes and chimps diverged along di erent evolutionary paths. That is signi cant becauseone of the things that made Ardi interesting scienti cally was that she had been identi edby White as the earliest known descendant of the last common ancestor of humans andAfrican apes — thus her physiology could o er clues to what makes humans di erentfrom their nearest relatives.

"[White] showed no evidence that Ardi is on the human lineage," Sarmiento says. "Thosecharacters that he posited as relating exclusively to humans also exist in apes and ape fossilsthat we consider not to be in the human lineage."

The biggest mistake White made, according to the paper, was to use outdated charactersand concepts to classify Ardi and to fail to identify anatomical clues that would rule herout as a human ancestor. As an example, Sarmiento says that on the base of Ardi's skull, theinside of the jaw joint surface is open as it is in orangutans and gibbons, and not fused tothe rest of the skull as it is in humans and African apes — suggesting that Ardi divergedbefore this character developed in the common ancestor of humans and apes.

White, no surprise, has defended his analysis, publishing a written response of his own inScience. In an e-mail exchange with TIME, he says, "Dr. Sarmiento's views appear to beuniquely his own. Most notable in Dr. Sarmiento's comment is his refusal to recognize assigni cant the multiple and independently derived features of the Ardipithecus cranium,dentition, and postcranial skeleton. These features uniformly align this primate with alllater hominids to the exclusion of any other ape — living or fossil. Has Dr. Sarmientoshown how the Ardipithecus evidence better ts his interpretation than the one wepublished? Not here."

But Sarmiento's is not the only attack on White's and his colleagues' work. In a separatecomment in Science, eight geologists and anthropologists from seven universities questionWhite's conclusion that Ardi lived in a wooded area rather than on open grassland. At thelaunch of the Ardi papers, White had argued that the wooded terrain Ardi called home


!"#$ %&'() *+(,-.(/./ 01233,-4, 5672- %-+,/.8& 08--,+.(8-


disproved the "savanna hypothesis" of bipedalism — the theory that what got our ancestorswalking on two legs in the rst place was a change in climate that transformed Africanforest into savanna. In such an environment, goes the reasoning, upright primates wouldhave had the advantage over knuckle walkers because they could see over tall grasses toavoid predators and search for food and carry it back to their homes.

Reached by Internet chat in Kenya, University of Utah geochemist Thure Cerling, leadauthor of the Science critique, accuses the Ardi team of misinterpreting its data. Carbonmeasures and other studies on the rock around the Ardi site suggest that tropical grassescontributed up to 77% of Ardi's ecosystem, Cerling says. While acknowledging that therewas evidence that woodland existed around Ardi as well, Cerling tells TIME that "earlyhumans had available to them, at no great distance, the resources of the savanna andprobably those of the riparian woodland as well." The savanna hypothesis, he adds, remains"a viable idea."

Responding to the critique, White accuses Cerling and his co-authors of "downplaying andignoring" evidence of forests around Ardi in order to "accommodate their long-heldhypothesis that earliest hominid evolution was savanna-driven." He adds that "we havenever claimed that there was no grass in Ardi's world," but rather that early hominidssimply had "preferences for — and adaptations to — woodland habitats."

While Sarmiento regards the hype around Ardi to have been overblown, Cerling says hestill feels the discovery and re-creation of the ancient specimen to be a monumentalbreakthrough. But, he says, the science was in the evidence collected by White andcolleagues, and not in their conclusions. "Many students will thoroughly examine the dataand will come to their own independent evaluations," he says. In other words, scienceworks a bit like evolution, and asking whether Ardi will survive as a major advancement israther like going into the distant past and asking what the fate of her species would be:Only time will tell.

MALCOLM RITTER, Associated Press


!"#$ %&'() *+(,-.(/./ 01233,-4, 5672- %-+,/.8& 08--,+.(8-

http://www.cleveland.com/nation/index.ssf/2010/05/ardi.html

NEW YORK -- Last fall, a fossil skeleton named"Ardi" shook up the eld of human evolution.Now, some scientists are raising doubts aboutwhat exactly the creature from Ethiopia was andwhat kind of landscape it inhabited.

New critiques question whether Ardi reallybelongs on the human branch of theevolutionary tree and whether it really lived inwoodlands. That second question hasimplications for theories about what kind ofenvironment spurred early human evolution.

The new work is being published by the journalScience, which last year declared the originalpresentation of the 4.4 million-year-old fossil tobe the magazine's breakthrough of the year.

Ardi, short for Ardipithecus ramidus, is a million years older than the famous "Lucy" fossil.Last October, it was hailed as a window on early human evolution.

Researchers concluded that "Ardi" walked upright rather than on its knuckles like chimps,for example, and that it lived in woodlands rather than open grasslands. It didn't lookmuch like today's chimps, our closest living relatives, even though it was closer than Lucyto the common ancestor of humans and chimps.


!"#$ %&'()*+,( -'*,. /0*('1 0-+&) 23/1*42

http://sciencemag.org/ardipithecus


Several Cleveland-area scientists played central roles in the discovery and analysis of theArdipithecus fossils, including Yohannes Haile-Selassie and Linda Spurlock of theCleveland Museum of Natural History; Case Western Reserve University professors BruceLatimer and Scott Simpson; and Kent State University anthropologist Owen Lovejoy.

Questioning of such discoveries isn't unusual; big scienti c nds are typically greeted thatway. Until more scientists can study the fossil and other work can be done, broadconsensus may be elusive.

Tim White of the University of California, Berkeley, one of the scientists who describedArdi last year in Science, said he isn't surprised by this week's debate.

"It was completely expected," he said. "Any time you have something that is as di erent asArdi, you're probably going to have it."

Esteban Sarmiento of the Human Evolution Foundation in East Brunswick, N.J., wrote inthe new analysis that he's not convinced Ardi belongs on the evolutionary tree branchleading to modern humans.

Instead, he said in an interview, he thinks it came along earlier, before that human branchsplit off from the ancestors of chimps and gorillas.

The speci c anatomical features of teeth, the skull and elsewhere that the researchers citedjust don't make a convincing case for membership on the human branch, he argued. Some,like certain features in the wrist and where the lower jaw connects to the skull, indicateinstead that Ardi arose before humans split off from African apes, he said.

In a written rebuttal in Science and in a telephone interview, White disagreed withSarmiento's conclusion. "The evidence is very clear that in Ardipithecus, there arecharacteristics shared only by later hominids . . . and humans," White said.


!"#$ %&'()*+,( -'*,. /0*('1 0-+&) 23/1*42


If Ardi were really ancestral to chimps, certain features of its teeth, pelvis, and skull wouldhave had to later evolve back to their more ape-like conditions, an "evolutionary reversalthat's highly unlikely," White said in an interview.

Two other experts, however, said in interviews that they think it's too early to tell whereArdi fits on the evolutionary tree.

Will Harcourt-Smith, a research associate at the American Museum of Natural Historyand a member of the anthropology department at Lehman College in New York, said hecould not say whether Sarmiento was right or wrong.

"It's early days" in the analysis of Ardi, he said. "Until there is a more complete descriptionof the skeleton, one has to be cautious about interpreting the initial analyses one way oranother . . . I still think it's open season."

Harcourt-Smith said he did disagree with Sarmiento's assertion that Ardi was probably tooold to belong to the human branch of the evolutionary tree.

Rick Potts, head of the human origins program at the Smithsonian Institution's NaturalHistory Museum, said Ardi is known chie y from just one site. And it lived during adimly understood period of evolution when there might have been "a lot ofexperimentation," he said.

Potts said that makes it hard to draw conclusions about how the species relates to Lucy andmodern humans.

"I think it's just too soon to tell exactly where it stands in relationship to the branchingpoint of humans from other African apes," he said.

The second critique focuses on Ardi's environment. Last year's analysis said it waspredominantly a woodland setting. So that argued against the "savanna hypothesis," theidea that early human ancestors started to walk upright because they lived on grassy plainsand savannas.


!"#$ %&'()*+,( -'*,. /0*('1 0-+&) 23/1*42


In this week's critique, geochemist Thure Cerling of the University of Utah and otherscientists said their reading of the evidence shows Ardi roamed in a savanna with no morethan 25 percent covered by a woody canopy. So they disagreed with last year's emphasis onthe leafy setting.

The critique focused on evidence like analysis of ancient soils, tooth enamel from animalsfound at the site and tiny silica grains found in plants.

In a published rebuttal and the interview, White agreed that Ardi's environment includedgrasslands but said the totality of the evidence shows Ardi preferred living in its woodedareas instead.

For example, the skeleton shows adaptations for climbing and "it wasn't climbing grass," hesaid. And animals found with Ardi's remains are mostly woodland creatures like leaf-eatingmonkeys, he said.

Potts said he thinks White is right about the environment of the site in dispute. But again,he said, that's just one site, and not enough for drawing conclusions about the generalenvironmental conditions of early human evolution -- if indeed White is also right aboutArdi's place on the family tree.


!"#$ %&'()*+,( -'*,. /0*('1 0-+&) 23/1*42


http://humanorigins.si.edu/evidence/human-family-tree

https://www.sciencenews.org/blog/context/human-ancestor-lucy-celebrates-40th-anniversary

Documents

(01) Ardipithecus ramidus | The Smithsonian · 2018. 9. 4. · Analysis of the skeleton reveals that humans did not evolve from knuckle-walking apes, ... reclassi/ed in 1995 because