• In particular, it has been used to suggest that the last common ancestor of hominids and African apes was characterized by relatively little aggression between males and between

  • Although not as closely related genetically as the knuckle walking apes, this would indicate that Ardi was behaviourly more similar to the orangutan than to the other three
    great apes.

  • Sarmiento noted that Ardipithecus does not share any characteristics exclusive to humans, and some of its characteristics (those in the wrist and basicranium) suggest it diverged
    from humans prior to the human–gorilla last common ancestor.

  • [14] The less pronounced nature of the upper canine teeth in A. ramidus has been used to infer aspects of the social behavior of the species and more ancestral hominids.

  • [31] Previously, it was assumed that such ancient human ancestors behaved much like chimps, but this is no longer considered to be a viable comparison.

  • [24] His comparative (narrow allometry) study in 2011 on the molar and body segment lengths (which included living primates of similar body size) noted that some dimensions
    including short upper limbs, and metacarpals are reminiscent of humans, but other dimensions such as long toes and relative molar surface area are great ape-like.

  • 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 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.

  • “Thus, fundamental reproductive and social behavioral changes probably occurred in hominids long before they had enlarged brains and began to use stone tools,” the research
    team concluded.

  • This is only seen in humans, so they argued that the species may show the first trend towards human social, parenting and sexual psychology.

  • However, because the “Ardi” skeleton is no more than 200,000 years older than the earliest fossils of Australopithecus, and may in fact be younger than they are,[17] some
    researchers doubt that it can represent a direct ancestor of Australopithecus.

  • Originally described as one of the earliest ancestors of humans after they diverged from the chimpanzees, the relation of this genus to human ancestors and whether it is a
    hominin is now a matter of debate.

  • [17] The fossil is regarded by its describers as shedding light on a stage of human evolution about which little was known, more than a million years before Lucy (Australopithecus
    afarensis), the iconic early human ancestor candidate who lived 3.2 million years ago, and was discovered in 1974 just 74 km (46 mi) away from Ardi’s discovery site.

  • They conceded that chimps and A. ramidus likely had 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.

  • [28] Evolutionary tree according to a 2019 study:[29] Paleobiology[edit] The Ardipithecus length measures are good indicators of function and together with dental isotope
    data and the fauna and flora from the fossil site indicate Ardipithecus was mainly a terrestrial quadruped collecting a large portion of its food on the ground.

  • [30] In 2015, Australian anthropologists Gary Clark and Maciej Henneberg said that Ardipithecus adults have a facial anatomy more similar to chimpanzee subadults than adults,
    with a less-projecting face and smaller canines (large canines in primate males are used to compete within mating hierarchies), and attributed this to a decrease in craniofacial growth in favour of brain growth.

  • [27] Comparison of the tooth root morphology with those of the earlier Sahelanthropus also indicated strong resemblance, also pointing to inclusion to the human line.

  • This is slightly smaller than a modern bonobo or female common chimpanzee brain, but much smaller than the brain of australopithecines like Lucy (~400 to 550 cm3) and roughly
    20% the size of the modern Homo sapiens brain.

  • [25] However, some later studies still argue for its classification in the human lineage.

  • Clark and Henneberg also argued that such shortening of the skull—which may have caused a descension of 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.

  • [3] Initial behavioral analysis indicated that Ardipithecus could be very similar to chimpanzees,[1] however more recent analysis based on canine size and lack of canine sexual
    dimorphism indicates that Ardipithecus was characterised by reduced aggression,[4] and that they more closely resemble bonobos.

  • [25] A comparative study in 2013 on carbon and oxygen stable isotopes within modern and fossil tooth enamel revealed that Ardipithecus fed both arboreally (on trees) and on
    the ground in a more open habitat, unlike chimpanzees.

  • It is not confirmed how many other features of its skeleton reflect adaptation to bipedalism on the ground as well.

  • [22] Classification[edit] Due to several shared characteristics with chimpanzees, its closeness to ape divergence period, and due to its fossil incompleteness, the exact position
    of Ardipithecus in the fossil record is a subject of controversy.

  • [15] A. ramidus existed more recently than the most recent common ancestor of humans and chimpanzees (CLCA or Pan-Homo LCA) and thus is not fully representative of that common

  • Like common chimpanzees, A. ramidus was much more prognathic than modern humans.

  • Nevertheless, it is in some ways unlike chimpanzees, suggesting that the common ancestor differs from the modern chimpanzee.

  • [9] In 1992–1993 a research team headed by Tim White discovered the first A. ramidus fossils—seventeen fragments including skull, mandible, teeth and arm bones—from the Afar
    Depression in the Middle Awash river valley of Ethiopia.

  • Researchers in a 2009 study said that this condition “compromises the living chimpanzee as a behavioral model for the ancestral hominid condition.

  • This is markedly different from social patterns in common chimpanzees, among which intermale and intergroup aggression are typically high.

  • Fleagle and Kappelman suggest that the region in which Ardi was found is difficult to date radiometrically, and they argue that Ardi should be dated at 3.9 million years.

  • The female raises offspring one at a time with a maturation period of about eight years.

  • The first fossil found was dated to 4.4 million years ago on the basis of its stratigraphic position between two volcanic strata: the basal Gaala Tuff Complex (G.A.T.C.)


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