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67-509: Dated to 3.7 million years ago, they were the oldest known evidence of hominin bipedalism at that time. Subsequently, older Ardipithecus ramidus fossils were found with features that suggest bipedalism. With the footprints there were other discoveries excavated at Laetoli including Hominina and animal skeletal remains. Analysis of the footprints and skeletal structure showed clear evidence that bipedalism preceded enlarged brains in Hominina. At

134-467: A polygynous society, hunt cooperatively, and are the most technologically advanced non-human . However, Clark and Henneberg concluded that Ardipithecus cannot be compared to chimps, having been too similar to humans. According to French paleoprimatologist Jean-Renaud Boisserie , the hands of Ardipithecus would have been dextrous enough to handle basic tools, though it has not been associated with any tools. The teeth of A. ramidus indicate that it

201-412: A bipedal gait for very long time intervals. It may have predominantly used palm walking on the ground, Nonetheless, A. ramidus still had specialized adaptations for bipedality, such as a robust fibularis longus muscle used in pushing the foot off the ground while walking ( plantarflexion ), the big toe (though still capable of grasping) was used for pushing off, and the legs were aligned directly over

268-408: A derived trait instead of basal (it evolved later rather than earlier), and is a specialized adaptation in modern great apes as a response to a different and more physically exerting lifestyle in males than females rather than being tied to interspecific conflict. Australian anthropologists Gary Clark and Maciej Henneberg argued that such shortening of the skull—which may have caused a descension of

335-452: A disposition towards polygyny. Half of the large mammal species associated with A. ramidus at Aramis are spiral-horned antelope and colobine monkeys (namely Kuseracolobus and Pliopapio ). There are a few specimens of primitive white and black rhino species, and elephants, giraffes and hippo specimens are less abundant. These animals indicate that Aramis ranged from wooded grasslands to forests, but A. ramidus likely preferred

402-496: A forearm to upper arm ratio similar to the Golden Ratio – greater than other hominins. They exhibited greater sexual dimorphism than members of Homo or Pan but less so than Gorilla or Pongo . It is thought that they averaged heights of 1.2–1.5 metres (3.9–4.9 ft) and weighed between 30 and 55 kilograms (66 and 121 lb). The brain size may have been 350 cc to 600 cc. The postcanines (the teeth behind

469-461: A form of bipedality more primitive than Australopithecus . The discovery of such unspecialized locomotion led American anthropologist Owen Lovejoy and colleagues to postulate that the chimpanzee–human last common ancestor used a similar method of locomotion. The upper pelvis (distance from the sacrum to the hip joint ) is shorter than in any known ape. It is inferred to have had a long lumbar vertebral series, and lordosis (human curvature of

536-486: A grasping big toe adapted for locomotion in the trees (an arboreal lifestyle), though it was likely not as specialized for grasping as it is in modern great apes. Its tibial and tarsal lengths indicate a leaping ability similar to bonobos. It lacks any characters suggestive of specialized suspension , vertical climbing, or knuckle walking ; and it seems to have used a method of locomotion unlike any modern great ape, which combined arboreal palm walking clambering and

603-404: A non-human primate, but later was revealed (in 1979, by P. Andrews and T. White) as the site's first fossil hominin . In 1938 and 1939, German archaeologist Ludwig Kohl-Larsen studied the site extensively. Several hominin remains, including premolars, molars, and incisors, were identified. A later excavation in 1959 revealed no new hominins, and Laetoli went relatively unexplored until 1974—when

670-508: A period of coexistence. In 1957, an Early Pleistocene Chinese fossil tooth of unknown province was described as resembling P. robustus . Three fossilized molars from Jianshi , China (Longgudong Cave) were later identified as belonging to an Australopithecus species. However further examination questioned this interpretation; Zhang (1984) argued the Jianshi teeth and unidentified tooth belong to H. erectus . Liu et al . (2010) also dispute

737-401: A process of self domestication (becoming more and more docile which allows for a more gracile build). Because a similar process is thought to have occurred with the comparatively docile bonobos from more aggressive chimps, A. ramidus society may have seen an increase in maternal care and female mate selection compared to its ancestors. Alternatively, it is possible that increased male size is

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804-401: A specialized diet. Also, the origins of bipedality were thought to have occurred due to a switch from a forest to a savanna environment, but the presence of bipedal pre- Australopithecus hominins in woodlands has called this into question, though they inhabited wooded corridors near or between savannas. It is also possible that Ardipithecus and pre- Australopithecus were random offshoots of

871-428: A species level, the identity of the Hominina who made the trace is difficult to construe precisely; Australopithecus afarensis is the species most commonly proposed. Laetoli was first recognized by western science in 1935 through a man named Sanimu, who convinced archeologist Louis Leakey to investigate the area. Several mammalian fossils were collected with a left lower canine tooth originally identified as that of

938-489: A subspecies of A. ramidus by Ethiopian paleoanthropologist Yohannes Haile-Selassie . In 2004, Haile-Selassie, Suwa and White split it off into its own species, A. kadabba . A. kadabba is considered to have been the direct ancestor of A. ramidus , making Ardipithecus a chronospecies . The exact affinities of Ardipithecus have been debated. White, in 1994, considered A. ramidus to have been more closely related to humans than chimpanzees, though noting it to be

1005-543: A then-novel way of preservation. The site was re-vegetated by acacia trees, which later gave rise to fears over root growth. In mid-1992, a GCI-Tanzanian team investigated this by opening a three-by-three meter trench, which showed that roots had damaged the footprints. However, the part of the trackway unaffected by root growth showed exceptional preservation. The success of the experiment led to an increased practice in reburials for preserving excavated sites. In 1993, measures were taken to prevent erosion. The original trackway

1072-542: Is a 75-foot (24-meter) line of Hominina fossil footprints, preserved in powdery volcanic ash originally thought to have been from an eruption of the nearby (20 km) Sadiman volcano . However, recent study of the Sadiman volcano has shown that it is not a source for the Laetoli Footprints Tuff (Zaitsev et al. 2011). Soft rain cemented the ash-layer (15 cm thick) to tuff without destroying

1139-406: Is a serious problem. Another problem presents itself in the fact that it has been very difficult to assess which hominid [now "hominin"] represents the first member of the genus Homo . Without knowing this, it is not possible to determine which species of australopithecine may have been ancestral to Homo . Marc Verhaegen has argued that an australopithecine species could have also been ancestral to

1206-424: Is ancestral to the genus Homo is a question that is a top priority for many paleoanthropologists, but one that will likely elude any conclusive answers for years to come. Nearly every possible species has been suggested as a likely candidate, but none are overwhelmingly convincing. Presently, it appears that A. garhi has the potential to occupy this coveted place in paleoanthropology, but the lack of fossil evidence

1273-450: Is correlated to increased parental care and monogamy in primates. It has also been suggested that it was among the earliest of human ancestors to use some proto-language, possibly capable of vocalizing at the same level as a human infant. This is based on evidence of human-like skull architecture, cranial base angle and vocal tract dimensions, all of which in A. ramidus are paedomorphic when compared to chimpanzees and bonobos. This suggests

1340-452: Is not enough evidence to assign Ardipithecus to Hominini (comprising both humans and chimps), but its closer affinities to humans have been reaffirmed in following years. White and colleagues consider it to have been closely related to or the ancestor of the temporally close Australopithecus anamensis , which was the ancestor to Au. afarensis . Before the discovery of Ardipithecus and other pre- Australopithecus hominins, it

1407-583: Is seen in some of the hottest, driest parts of East Africa. Carbon isotope analyses of the herbivore teeth from the Gona Western Margin associated with A. ramidus indicate that these herbivores fed mainly on C4 plants and grasses rather than forest plants. The area seems to have featured bushland and grasslands. Hominina Hominina Gray 1825 sensu Andrew & Harrison 2005 The australopithecines , formally Australopithecina or Hominina , are generally any species in

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1474-534: Is the species of the three hominins who made the footprints at Laetoli. This conclusion is based on the reconstruction of the foot skeleton of a female A. afarensis hominin by anthropologists Tim D. White and Gen Suwa of the University of California, as well as detailed footprint analysis by Russel Tuttle of the University of Chicago; he compared human and other bipedal animals such as bears and primates, including gaits and foot structure, and taking into account

1541-851: The genera Ardipithecus , Orrorin , Sahelanthropus , and Graecopithecus are the possible ancestors of the australopithecines. Classification of subtribe Australopithecina according to Briggs & Crowther 2008 , p. 124. Phylogeny of Hominina/Australopithecina according to Dembo et al . (2016). Sahelanthropus tchadensis Ardipithecus Australopithecus anamensis Australopithecus afarensis Australopithecus garhi Kenyanthropus platyops Plesianthropus transvaalensis ( Australopithecus africanus ) Paranthropus aethiopicus Paranthropus robustus Paranthropus boisei Homo (including "Australopithecus" sediba ) The post-cranial remains of australopithecines show they were adapted to bipedal locomotion , but did not walk identically to humans. They had

1608-407: The larynx —as well as lordosis—allowing better movement of the larynx—increased vocal ability, significantly pushing back the origin of language to well before the evolution of Homo . They argued that self domestication was aided by the development of vocalization, living in a pro-social society, as a means of non-violently dealing with conflict. They conceded that chimps and A. ramidus likely had

1675-499: The "gracile australopithecines", while Paranthropus are called the "robust australopithecines". The australopithecines occurred in the Late Miocene sub-epoch and were bipedal , and they were dentally similar to humans, but with a brain size not much larger than that of modern non-human apes , with lesser encephalization than in the genus Homo . Humans (genus Homo ) may have descended from australopithecine ancestors and

1742-530: The 4.4-million-year-old (Ma) deposits of the Afar region in Aramis, Ethiopia from 1992 to 1993, making them the oldest hominin remains at the time, surpassing Australopithecus afarensis . They initially classified it as Australopithecus ramidus , the species name deriving from the Afar language ramid "root". In 1995, they made a corrigendum recommending it be split off into a separate genus, Ardipithecus ;

1809-597: The Naibadad Beds, but they are correlated with a bed layer at Olduvai Gorge based on mineral content. Pleistocene fauna and Acheulean artifacts have been found in the Olpiro Beds. Based on a trachytic tuff which occurs within the beds, the Ngaloba Beds may therefore be dated between 120,000 and 150,000 years BP. The principal discovery, made by Mary Leakey and her team in 1976 (and fully excavated by 1978),

1876-455: The animals are represented by skeletal remains discovered in the area. No artifacts have been found in the vicinity, at least within the ancient Laetolil Beds that contain the trackway. However, artifacts from the younger Olpiro and Ngaloba Beds, also preserved at Laetoli, have been found. Before the discovery of the Laetoli footprints, there was much debate as to which developed first in

1943-406: The ankles instead of bowing out like in non-human great apes. The reduced canine size and reduced skull robustness in A. ramidus males (about the same size in males and females) is typically correlated with reduced male–male conflict, increased parental investment, and monogamy . Because of this, it is assumed that A. ramidus lived in a society similar to bonobos and ateline monkeys due to

2010-548: The canines) were relatively large, and had more enamel compared to contemporary apes and humans, whereas the incisors and canines were relatively small, and there was little difference between the males' and females' canines compared to modern apes. Most scientists maintain that the genus Homo emerged in Africa within the australopithecines around two million years ago. However, there is no consensus on within which species: Determining which species of australopithecine (if any)

2077-504: The cats Dinofelis and Megantereon , the dog Eucyon , and crocodiles. Bayberry , hackberry and palm trees appear to have been common at the time from Aramis to the Gulf of Aden ; and botanical evidence suggests a cool, humid climate. Conversely, annual water deficit (the difference between water loss by evapotranspiration and water gain by precipitation) at Aramis was calculated to have been about 1,500 mm (59 in), which

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2144-503: The characteristics of obligate bipedalism: pronounced heel strike from deep impressions, lateral transmission of force from the heel to the base of the lateral metatarsal , a well-developed medial longitudinal arch, adducted big toe, and a deep impression for the big toe commensurate with toe-off. Two dating techniques were used to arrive at the approximate age of the beds that make up the ground layers at Laetoli: potassium-argon dating and analysis of stratigraphy . Based on these methods,

2211-418: The closed habitats, specifically riverine areas as such water sources may have supported more canopy coverage. Aramis as a whole generally had less than 25% canopy cover. There were exceedingly high rates of scavenging, indicating a highly competitive environment somewhat like Ngorongoro Crater . Predators of the area were the hyenas Ikelohyaena abronia and Crocuta dietrichi , the bear Agriotherium ,

2278-489: The common assumption of a nuclear family . Roberto Sáez claims that this 27-metre trail of about 70 footprints was left by two Australopithecus walking in front, while the third hominid walked behind, superimposing its steps on the footprints left by one of the two in front. He acknowledges that it will never be possible to prove that this is true. The footprints demonstrate that the Hominina habitually walked upright as there are no knuckle-impressions. The feet do not have

2345-475: The conclusion that the recognition of australopithecines in Asia would not confuse but could help to clarify the early evolution of hominids ["hominins"] on that continent. This concept would explain the scanty remains from Java and China as relic of an Asian offshoot of an early radiation of Australopithecus , which was followed much later by an [African] immigration of Homo erectus , and finally became extinct after

2412-537: The discovery of a hominin premolar by George Dove revived interest in the site. Mary Leakey returned and almost immediately discovered the well-preserved remains of hominins. In 1978, Leakey's 1976 discovery of hominin tracks—"The Laetoli Footprints"—provided convincing evidence of bipedalism in Pliocene hominins and gained significant recognition by both scientists and laymen. Although much debated, researchers have tentatively concluded that Australopithecus afarensis

2479-480: The extinct, close relatives of modern humans and, together with the extant genus Homo , comprise the human clade . Members of the human clade, i.e. the Hominini after the split from the chimpanzees, are called Hominina ( see Hominidae; terms "hominids" and hominins ). While none of the groups normally directly assigned to this group survived, the australopithecines do not appear to be literally extinct (in

2546-493: The genus Pan (i.e. chimpanzees). A minority view among palaeoanthropologists is that australopithecines moved outside Africa. One proponent of this theory is Jens Lorenz Franzen , formerly Head of Paleoanthropology at the Research Institute Senckenberg . Franzen argued that robust australopithecines had reached not only Indonesia, as Meganthropus , but also China: In this way we arrive at

2613-470: The hominin line. Assuming subsistence was primarily sourced from climbing in trees, A. ramidus may not have exceeded 35–60 kg (77–132 lb). "Ardi," a larger female specimen, was estimated to have stood 117–124 cm (3 ft 10 in – 4 ft 1 in) and weighed 51 kg (112 lb) based on comparisons with large-bodied female apes. Unlike the later Australopithecus but much like chimps and humans, males and females were about

2680-456: The human evolutionary time line: a larger brain or bipedalism. The discovery of these footprints settled the issue, proving that the Laetoli hominins were fully bipedal long before the evolution of the modern human brain, and were bipedal close to a million years before the earliest known stone tools were made. The footprints were classified as possibly belonging to Australopithecus afarensis . Some analysts have noted in their interpretations that

2747-524: The layers have been named as follows, starting with the deepest: Lower Laetolil Beds, Upper Laetolil Beds, Lower Ndolanya Beds, Upper Ndolanya Beds, Ogol lavas, Naibadad Beds, Olpiro Beds, and Ngaloba Beds; it is the ancient Laetolil Beds that contain the footprints trackway. The upper unit of the Laetolil Beds dated back 3.6 to 3.8 million years ago. The beds are dominantly tuffs and have a maximum thickness of 130 meters. No mammalian fauna were found in

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2814-644: The lower unit of the Laetolil Beds, and no date could be assigned to this layer. The Ndolanya Beds, which are located above the Laetolil Beds and underlie the Ogol lavas, are clearly divisible into upper and lower units separated by a widespread deposit of calcrete up to one meter thick. However, like the Lower Laetolil Beds, no date can be assigned to the Ndolanya Beds. The Ogol lavas date back 2.4 million years. No fauna or artifacts are known from

2881-429: The making of the footprints. Pliocene sediments show that the environment was more moist and productive than now. Climate changes that caused a shift from forest to grassland environments have a strong correlation with upright posture and bipedalism in hominins. This could have initiated the evolution to bipedalism of the hominins found at Laetoli. In 1979, after the Laetoli footprints were recorded, they were re-buried as

2948-439: The mobile big toe of apes; instead, they have an arch (the bending of the sole of the foot) typical of modern humans. The hominins seem to have moved in a leisurely stroll. Computer simulations based on information from A. afarensis fossil skeletons and the spacing of the footprints indicate that the Hominina were walking at 1.0 m/s or above, which matches human walking speeds. The results of other studies have also supported

3015-441: The most ape -like fossil hominin to date. In 2001, French paleontologist Brigitte Senut and colleagues aligned it more closely to chimpanzees , but this has been refuted. In 2009, White and colleagues reaffirmed the position of Ardipithecus as more closely related to modern humans based on dental similarity, a short base of the skull , and adaptations to bipedality . In 2011, primatologist Esteban Sarmiento said that there

3082-491: The name stems from Afar ardi "ground" or "floor". The 4.4-million-year-old female ARA-VP 6/500 (" Ardi ") is the most complete specimen. Fossils from at least nine A. ramidus individuals at As Duma , Gona Western Margin , Afar, were unearthed from 1993 to 2003. The fossils were dated to between 4.32 and 4.51 million years ago. In 2001, 6.5- to 5.5-million-year-old fossils from the Middle Awash were classified as

3149-411: The prints. In time, they were covered by other ash deposits. The fossil footprints were rather whimsically discovered by Yale's Andrew Hill when visiting Mary Leakey in 1976. While walking back to camp one evening, Hill fell trying to avoid a large ball of elephant dung thrown at him by a colleague. With his face only inches from the rock, he recognized footprints made by antelopes and rhinos preserved in

3216-666: The related genera of Australopithecus and Paranthropus . It may also include members of Kenyanthropus , Ardipithecus , and Praeanthropus . The term comes from a former classification as members of a distinct subfamily, the Australopithecinae. They are classified within the Australopithecina subtribe of the Hominini tribe . These related species are sometimes collectively termed australopithecines , australopiths or homininans . They are

3283-410: The rest of the body into adulthood; and considered this evidence of a switch from a gross skeletal anatomy trajectory to a neurological development trajectory due to selective pressure for sociability. Nonetheless, their conclusions are highly speculative. American primatologist Craig Stanford postulated that A. ramidus behaved similarly to chimps, which frequent both the trees and the ground, have

3350-406: The same as the human foot, which is much different from the feet of chimpanzees and other non-bipedal beings. The footprint impression has been interpreted as the same as the modern human stride, with the heel striking first and then a weight transfer to the ball of the foot before pushing off the toes. Based on stratigraphic analysis, the findings also provide insight into the climate at the time of

3417-426: The same size. A. ramidus had a small brain, measuring 300–350 cc (18–21 cu in). This is slightly smaller than a modern bonobo or chimp brain, but much smaller than the brain of Australopithecus — about 400–550 cc (24–34 cu in)—and roughly 20% the size of the modern human brain. Like chimps, the A. ramidus face was much more pronounced ( prognathic ) than modern humans. The size of

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3484-541: The same underlying changes in skull architecture. A. ramidus appears to have inhabited woodland and bushland corridors between savannas, and was a generalized omnivore . The first remains were described in 1994 by American anthropologist Tim D. White , Japanese paleoanthropologist Gen Suwa , and Ethiopian paleontologist Berhane Asfaw . The holotype specimen , ARA-VP-6/1, comprised an associated set of 10 teeth; and there were 16 other paratypes identified, preserving also skull and arm fragments. These were unearthed in

3551-402: The same vocal capabilities, but said that A. ramidus made use of more complex vocalizations, and vocalized at the same level as a human infant due to selective pressure to become more social. This would have allowed their society to become more complex. They also noted that the base of the skull stopped growing with the brain by the end of juvenility, whereas in chimps it continues growing with

3618-407: The sense of having no living descendants) as the genera Kenyanthropus , Paranthropus and Homo probably emerged as sister of a late Australopithecus species such as A. africanus and/or A. sediba . The terms australopithecines, et. al., come from a former classification as members of a distinct subfamily, the Australopithecinae. Members of Australopithecus are sometimes referred to as

3685-400: The smaller trail bears "telltale signs that suggest whoever left the prints was burdened on one side." This may suggest that a female was carrying an infant on her hip but this cannot be proven for certain. The footprints themselves were an unlikely discovery because they closely resemble modern human footprints, despite being almost 4 million years old. It is noted that the toe pattern is much

3752-471: The spine), which are adaptations for bipedality. However, the legs were not completely aligned with the torso (were anterolaterally displaced), and Ardipithecus may have relied more on its quadriceps than hamstrings which is more effective for climbing than walking. However, it lacked foot arches and had to adopt a flat-footed stance. These would have made it less efficient at walking and running than Australopithecus and Homo . It may not have employed

3819-505: The theory of a human-like gait . In 2015, footprints of the same age as the first reported footprints were unearthed at a site approximately 150 meters south of the original site G footprints. This site is called site S, and the 2 individuals who made the prints are named S1 and S2. S2 is represented by only 1 print, but S1 left a track of prints, the first 4 of which are shown in the composite image, along with an analysis of step and stride lengths. Further analysis indicated that individual S1

3886-583: The track and moving it to an enclosed site have been suggested, but the cost is viewed as outweighing the benefits: the process would require much research, a large amount of money, and there is a risk of loss or damage. Thus, burial seems to be the most effective method of preservation. Ardipithecus ramidus Ardipithecus ramidus is a species of australopithecine from the Afar region of Early Pliocene Ethiopia 4.4 million years ago (mya). A. ramidus , unlike modern hominids , has adaptations for both walking on two legs ( bipedality ) and life in

3953-515: The trees ( arboreality ). However, it would not have been as efficient at bipedality as humans , nor at arboreality as non-human great apes . Its discovery, along with Miocene apes, has reworked academic understanding of the chimpanzee–human last common ancestor from appearing much like modern-day chimpanzees , orangutans and gorillas to being a creature without a modern anatomical cognate. The facial anatomy suggests that A. ramidus males were less aggressive than those of modern chimps, which

4020-403: The trend toward paedomorphic or juvenile-like form evident in human evolution, may have begun with A. ramidus . Given these unique features, it has been argued that in A. ramidus we may have the first evidence of human-like forms of social behaviour, vocally mediated sociality as well as increased levels of prosociality via the process of self-domestication—all of which seem to be associated with

4087-413: The upper canine tooth in A. ramidus males was not distinctly different from that of females (only 12% larger), in contrast to the sexual dimorphism observed in chimps where males have significantly larger and sharper upper canines than females. A. ramidus feet are better suited for walking than chimps. However, like non-human great apes, but unlike all previously recognized human ancestors, it had

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4154-425: The use of footwear. For gait Tuttle looked at the step length, stride length, stride width, and foot angle, and determined that A. afarensis was more human-like in gait than ape-like. A. afarensis is an obligate bipedal hominin with the beginnings of sexual dimorphism attributed to its species, and brain size very similar to that of modern chimpanzees and gorillas . Analysis of the Laetoli footprints indicated

4221-416: The volcanic ash, and among these, hominid footprints. The Hominina prints were produced by three individuals, one walking in the footprints of the other, making the preceding footprints difficult to recover. As the tracks lead in the same direction, they might have been produced by a group visiting a waterhole together, but there is nothing—or very little (see below, Interpretation and significance)—to support

4288-533: Was assumed that the chimpanzee–human last common ancestor and preceding apes appeared much like modern-day chimpanzees , orangutans and gorillas , which would have meant these three changed very little over millions of years. Their discovery led to the postulation that modern great apes, much like humans, evolved several specialized adaptations to their environment (have highly derived morphologies ), and their ancestors were comparatively poorly adapted to suspensory behavior or knuckle walking, and did not have such

4355-544: Was considerably larger than any of the three individuals from site G. Other prints show the presence of twenty different animal species besides the hominin A. afarensis , among them hyenas , wild cats ( Machairodus ), baboons , wild boars , giraffes , gazelles , rhinos , several kinds of antelope , Hipparion , buffaloes , elephant relatives (of the extinct genus Deinotherium ), hares and birds . Rain-prints can be seen as well. Few footprints are superimposed, which indicates that they were rapidly covered up. Most of

4422-491: Was likely a generalized omnivore and fruit eater which predominantly consumed C3 plants in woodlands or gallery forests . The teeth lacked adaptations for abrasive foods. Lacking the speed and agility of chimps and baboons, meat intake by Ardipithecus , if done, would have been sourced from only what could have been captured by limited pursuit, or from scavenging carcasses. The second-to-fourth digit ratios of A. ramidus are low, consistent with high androgenisation and

4489-446: Was remolded and new casts were made. As the trackway is very fragile, the new replica cast was used to guide re-excavation in the field. A team of specialists, one being Fiona Marshall , re-excavated half of the trackway to record its condition, stabilize the surface, extract dead roots and rebury it with synthetic geotextile materials. This allows the trackway surface to breathe, and protects it against root growth. Proposals for lifting

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