Hominid fossils predating the emergence of Australopithecus have been sparse and fragmentary. The evolution of our lineage after the last common ancestor. White, T. D., Lovejoy, C. O., Suwa, G., WoldeGabriel, G., Asfaw, B., Beyene, Y., & Haile-Selassie, Y. (). Ardipithecus ramidus and the Paleobiology of Early. Darwin’s human evolution scenario attempted to explain hominid tool () Ardipithecus ramidus and the paleobiology of early hominids.
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Ardipithecus ramidus and the birth of humanity. A famous French palaeontologist often recounts the reaction of his offended grandmother after he told her about human evolution: In a spectacular set of 11 articles published in the magazine Science in Octoberan international research team put an end to this paradigm.
This species is not the oldest known human ancestor, and it was initially described 16 years ago White et al. However, species novelty and greater antiquity are not absolute requirements for establishing scientific significance: They throw an unprecedented light on our origins by extensively documenting the poorly known morphology of an evolutionary stage that preceded that of Australopithecus. This brief report comes back to this major discovery and its implications, and rectifies certain incorrect or inadequate eqrly to the topic by some news reports see Box: After the formal description of Au.
Our last earlj ancestor with the chimpanzees LCA was a forest-dwelling species roughly chimp-like morphologically speaking and living sometime before 4 Ma million years ago. Following the LCA, our direct ancestors split from those of chimpanzees, and developed an advanced biped posture as an adaptation to the developing savannah thw eastern Africa. This was the earliest stage of human evolution, essentially represented by Australopithecus Fig.
In the later stage Homo. This was a eatly, neat story. Between andseveral publications unveiled new ancient human ancestors from Ethiopia and Kenya in eastern Africa, ardipithscus from Chad in central Africa. Some EHA were the oldest recognized bipeds living in a forested environment such as Orrorin, found in Kenya by Pickford and Senut, The oldest of them. Sahelanthropus tchadensis, about twice as older as Lucy, was found in the heart of Africa, in Aand, in a completely different environmental setting Brunet et al.
This finding pushed back the age of the LCA sometimes before 7 Ma, making the interpretation of the consequences of environmental changes on human evolution trickier. The ardipitheccus environments of that time are considerably lesser known than more recent ones.
Uncertainty on the details of human evolution was therefore paradoxically increased by the new discoveries, which were all but fragmentary with the outstanding exception of S. Still, the available evidence would not tell us much about the evolution of the main feature used to characterize fossil humanity: This created a great deal of anxious expectation in the scientific community, as it took 14 years from the collection of the last skeleton fragment until its publication in Science This delay was hardly surprising given that the very fragile condition of the fossil required extremely careful and time-consuming preparation work.
It was decisive for this paleobjology to be completed with extreme care in order to be able to retrieve as much information as possible. A similarly careful analysis of every part of the skeleton was conducted.
Ardipithecus ramidus and the Paleobiology of Early Hominids – Dimensions
Ardi and the birth of humanity involving comparisons, measurements, photographs, CT-scan, computer reconstruction of ov parts and bone associations, analyses of enamel chemical contents, and the examination of microscopic food wear on teeth.
That was not all: Therefore, geologists scrutinized the sediments of Aramis in order to understand when and how they formed, while palaeontologists analysed thousands of animal and plant fossils collected with Ardi in order to understand the Afar biodiversity and landscape at 4.
In order to pile up this wealth of data, field research has been conducted until recently and is still ongoing at Aramis. Even though Science published 11 papers, these are preliminary presentations summarizing the most important aspects of the morphology and context of. In-depth descriptions and assessments will be presented in a forthcoming monograph. The habitat of Ardipithecus ramidus.
At Aramis, the EHA fossils were retrieved from a well-constrained layer of sediments sandwiched between two volcanic ash beds, both dated at 4. The careful study of the layer nature and content indicated that this layer was formed in one single environment and remained later undisturbed. This is a particularly fortunate occurrence, as many African fossil sites reflect a variety of environments.
In most cases, fossils deposited over a relatively long period of time during which environmental changes occurred, or they originated in other locations with different environments and were then transported to the sites. The geochemical signature of the fossil soils at Aramis supports an environment with some moderate amount of grass. Fossilized microscopic and macroscopic plant remains are dominated by fig, palm, and hackberry trees WoldeGabriel et al. It thus appears that Ardi lived and died in a more or less patchy forest — definitely neither a savannah nor a tropical rainforest, but a somehow dryer and more open woodland than the latter.
The ways hpminids life of these animals are congruent with an environment dominated by trees. The relative rarity of aquatic elements implies the absence of large water bodies in this environment. The study of contemporaneous deposits from nearby localities earlg more open environments surrounding large rivers. Until now, no remains of Ar. What were the EHA morphological adaptations corresponding to these needs? The look of our origins. The different individuals sampled at Aramis provide valuable information on ardipitjecus morphological differences between male and female Ar.
Males and females were about the same size, contrarily to later human ancestors White et al. On the basis of several anatomical features, the following partial skeleton was found to be that of a female.
Images courtesy of Berhane Asfaw. According to our previous knowledge, the cranial morphology of Ar. The braincase is as small as in chimpanzees: The details of its base are yet close to what is seen in Sahelanthropus and. Australopithecus, with a relatively forward aperture for the spinal chord, a position linked to a biped posture.
The face is moderately projected forward, although less than in extant African apes gorilla and chimpanzee. This trait is probably related to canine development and use. Ardi and the birth of humanity In male African apes, the upper canine is particularly large and sharpened compared to that of females. It is used for display and fight during recurrent agonistic interactions between males.
The available fossil sample indicates that male. This is strongly suggestive of a social behaviour in which fights between males were much less prominent than in African apes White et al.
With relatively small incisors and large molars compared to chimpanzees, Ar. This appears consistent with food sources equally found in trees and on the ground White et al. The hands of Ar. First, chimps generally move in trees by using their hands as hooks, suspending their bodies in vertical position. By opposition, quadruped human babies and monkeys use their hand palms.
Besides a relatively shorter thumb Fig. These were well adapted to careful tree climbing close to the way we, modern humans, climb trees and probably retained armidus locomotor function on the ground. There are no reasons to think that these hands could not efficiently handle basic forms of tools. The hip bone of Ar.
Its upper part is shallow and flared, getting close to the biped condition seen in Au. On the contrary, the lower part remained well developed for the attachment of muscles particularly utilized during climbing.
Ardipithecus ramidus and the paleobiology of early hominids.
It retained a relative aripithecus, and was well adapted to move on the ground Lovejoy et al. Still, it displays an opposing big toe, particularly useful for raamidus frequent climber Fig.
Such morphology is closer to monkeys than to the morphology of chimps and gorillas, which evolved a foot that is much more similar to a human hand. Ardipithecus ramidusthe LCA and the emergence of humans and chimpanzees. To summarize its locomotor abilities, Ar. A picture in sharp contrast with the locomotion of a chimpanzee that uses its hands to hang from trees and becomes a quadruped knuckle walker on the ground!
Jean-Renaud Boisserie This new piece of information offered by Ar.
It was probably more similar to monkeys than to apes in its limb proportions, and was an skilful climber who was able to support its weight with its palms in the trees Lovejoy et al. In relation to vertical suspension, their wrists became stronger and their arms elongated while their legs shortened.
The age of the LCA Last Common Ancestor with chimpanzees is tentative, and the characters reconstructed for it are inferred from the skeletal morphology of Ardipithecus ramidus and other early prehumans. Some significant fossil landmarks of our evolutionary history are numbered from 1 to 5. Arrows indicate the evolution of some major morphological features. The grey box indicates some of the main changes in behaviour and reproductive physiology that may have characterized the human lineage according to Lovejoy The question mark indicates our current lack of ancient fossil chimpanzees.
Extant humans, on the contrary, display many primitive features compared to their closest relatives, which we directly inherited from the LCA. This is particularly true for our hands, but in some aspects also for our feet.
Even when considering our derived features linked to our efficient bipedalism ardipithecux shorter arms and running abilityour supposedly unique shape is heavily marked by our arboreal origins Lovejoy et al. Ardi and the birth of humanity In light of these pf elucidated changes, what could have been the causes of the evolution of bipedalism in early human ancestors? In the concluding article of the. Science issue on Ardi, Owen Lovejoy — the Middle Awash team specialist of primate locomotion — proposed his own explanation, based on an impressive array of physiological, behavioural, and fossil evidence Lovejoy, According to this explanation, apes living after 8 Ma had to face an increasing problem: Their habitats, previously strictly arboreal, became progressively more terrestrial.
Chimpanzee ancestors retained a preferentially fruitrich diet Fig. On the ground, these apes independently evolved knucklewalking, a quadrupedal gait linked to their suspensory locomotion in trees. Males used to secure access to females and ardipkthecus through antagonistic interactions with other males using their large, sharp canines. Early human ancestors EHA followed a completely different path Fig.
They retained an omnivorous diet comparatively rich in fat and proteins consiting of a variety of plant and animal materials, possibly including small vertebrates. Paleobiologyy increasingly large ground territories, biped walk and hand dexterity allowed carrying substantial amounts of food. Males used a different strategy xrdipithecus gaining female attention: