Australopithecus afarensis
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| Australopithecus afarensis ("Lucy"){{#if:{{{status|}}}| {{#switch:{{{status}}}
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Australopithecus afarensis is a hominid which lived between 3.9 to 3 million years ago belonging to the genus Australopithecus, of which the first skeleton was discovered on November 24, 1974 by Donald Johanson, Yves Coppens and Tim White in the Middle Awash of Ethiopia's Afar Depression. They named it "Lucy" in reference to the famous Beatles song "Lucy in the Sky with Diamonds", which was played as they celebrated the find.
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Lucy's discovery
Donald Johanson, an American anthropologist who is now head of the Institute of Human Origins of Arizona State University, and his team, surveyed Hadar, Ethiopia during the late 1970s for evidence in interpreting Human origins. On November 24, 1974 near the River Awash, Don was planning on updating his field notes but instead one of his students Tom Gray accompanied him to find fossil bones. Both of them were on the hot arid plains surveying on the dusty terrain when a fossil caught both their eyes; arm bone fragments on a slope. As they looked further, more and more bones were found, including a jaw, arm bone, a thighbone, ribs, and vertebrae. Both Don and Tom had carefully analyzed the partial skeleton and calculated that an amazing 40% of a hominin skeleton was recovered, which, while sounding generally unimpressive, is astounding in the world of anthropology. When fossils are discovered usually only a few fragments are found; rarely are any skulls or ribs intact. The team proceeded to further analysis and Don noticed the feminine stature of the skeleton and argued that it was a female. He then nicknamed it Lucy, after the Beatles song "Lucy in the Sky with Diamonds". Lucy was only 3 feet 8 inches (1.1 m) tall, weighed 29 kilograms (65 lb) and looked somewhat like a Common Chimpanzee, but the observations of her pelvis proved that she had walked upright and more in the manner of humans.
Don Johanson placed Australopithecus afarensis as the last ancestor common to humans and chimpanzees living from 3.9 to 3 million years ago. Although fossils closer to the chimpanzee line have been recovered since the early 1970s, Lucy remains a treasure among anthropologists studying Human origins. The fragmentary nature of the older fossils furthermore deter confident conclusions as to the degree of bipedality or their relation to true hominines.
Johanson brought the skeleton back to Cleveland, under agreement with the government of the time in Ethiopia, and returned it according to agreement some 9 years later. Lucy was the first fossil hominin to really capture public notice, becoming almost a household name at the time. Current opinion is that the Lucy skeleton should be classified in the species Australopithecus afarensis. Lucy is preserved at the national Museum in Addis Ababa, Ethiopia. A plaster replica is displayed instead of the original skeleton. A diorama of Australopithecus afarensis and other human predecessors showing each species in its habitat and demonstrating the behaviors and capabilities that scientists believe it had is in the Hall of Human Biology and Evolution at the American Museum of Natural History in New York City.
Physical characteristics
Chimp-sized brain
One of the most striking characteristics possessed by Lucy was that she had a small skull, bipedal knee structure, and molars and front teeth of human (rather than great ape) style and relative size, but a small skull and small body. The image of a bipedal hominid with small skull, but teeth like a human, was quite a revelation to the paleoanthropological world at the time.
This was due to the earlier belief (1950-1970's) that increasing brain size of apes was the trigger for evolving towards humans. Before Lucy, a fossil called '1470' (Homo rudolfensis) with a brain capacity of about 800 cubic centimetres had been discovered, an ape with a bigger brain. If the older theory was correct, humans most likely evolved from the latter. However, it turned out Lucy was the older fossil, yet Lucy was bipedal (walked upright) and had a brain of only around 375 to 500 cc. These facts provided a basis to challenge the older views.
Bipedalism
There are differing views on how Lucy or her ancestors first became bipedal full-time.
The so-called 'savanna theory' on how A. afarensis evolved bipedalism hangs on the evidence that around 6 to 8 million years ago there seems to have been a mass extinction of forest dwelling creatures including the oldest hominins recognizable: Sahelanthropus tchadensis and Orrorin tugenensis. This triggered a burst of adaptive radiation, an evolutionary characteristic that generates new species quickly. Lucy's genetic forebears were tree dwelling apes, but in Lucy's world the trees would have been much fewer, and Lucy would have been forced to find a living on the flat savanna. Being bipedal would have had evolutionary advantages. For example, with the eyes higher up, she could see further than quadrupeds. Bipedalism also saves energy. The disadvantages of bipedalism were great—Lucy was the slowest moving primate of her time, for example, but according to the hypothesis, the advantages of bipedalism must have outweighed the disadvantages.
There had previously been problems in the past with designating Australopithecus afarensis as a fully bipedal hominine. In fact these hominines may have occasionally walked upright but still walked on all fours like apes; the curved fingers on A. afarensis are similar to those of modern-day apes, which use them for climbing trees. The phalanges (finger bones) aren't just prone to bend at the joints, but rather the bones themselves are curved. Another aspect of the Australopithecus skeleton that differs from human skeleton is the iliac crest of the pelvic bones. The iliac crest, or hip bone, on a Homo sapiens extends front-to-back, allowing an aligned gait. A human walks with one foot in front of the other. However, on Australopithecus and on other ape and ape-like species such as the orangutan, the iliac crest extends laterally (out to the side), causing the legs to stick out to the side, not straight forward. This gives a side-to-side rocking motion as the animal walks, not a forward gait.
The so-called aquatic ape theory compares the typical elements of human locomotion (truncal erectness, aligned body, two-leggedness, striding gait, very long legs, valgus knees, plantigrady etc.) with those of chimpanzees and other animals, and proposes that human ancestors evolved from vertical wader-climbers in coastal or swamp forests to shoreline dwellers who collected coconuts, turtles, bird eggs, shellfish etc. by beach-combing, wading and diving. In this view, the australopithecines largely conserved the ancestral vertical wading-climbing locomotion in swamp forests ("gracile" kind, including Australopithecus afarensis and A. africanus) and later more open wetlands ("robust" kind, including Paranthropus boisei and P. robustus). Meanwhile, Plio-Pleistocene Homo had dispersed along the African Rift valley lakes and African and Indian ocean coasts, from where different Homo populations ventured inland along rivers and lakes. However, this theory is not taken seriously by anthropologists.
Social characteristics
These hominines were likely to be somewhat like modern Homo sapiens when it came to the matter of social behaviour, yet like modern day apes they relied on the safety of trees from predators such as lions.
Site 333
Australopithecus afarensis fossils have only been discovered within Eastern Africa, which include Ethiopia (Hadar, Aramis), Tanzania (Laetoli) and Kenya (Omo, Turkana, Koobi Fora and Lothagam). A major discovery made by Don Johanson after Lucy's find he discovered the "First Family" including 200 hominid fragments of A. afarensis, discovered near Lucy on the other side of the hill in the Afar region. The site is known as "site 333", by a count of fossil fragments uncovered, such as teeth and pieces of jaw. 13 individuals were uncovered and all were adults, with no injuries caused by carnivores. All 13 individuals seemed to have died at the same time, thus Don concluded that they might have been killed instantly from a flash flood.
Related work
Further findings at Afar, including the many hominin bones in site 333, produced more bones of concurrent date, and led to Johanson and White's eventual argument that the Koobi Fora hominins were concurrent with the Afar hominins. In other words, Lucy was not unique in evolving bipedalism and a flat face.
Recently, an entirely new species has been discovered, called Kenyanthropus platyops, however the cranium KNM WT 40000 has a much distorted matrix making it hard to distinguish (however a flat face is present). This had many of the same characteristics as Lucy, but is possibly an entirely different genus.
Another species, called Ardipithecus ramidus, has been found, which was fully bipedal, yet appears to have been contemporaneous with a woodland environment, and, more importantly, contemporaneous with Australopithecus afarensis. Scientists have not yet been able to draw an estimation of the cranial capacity of A. ramidus as only small jaw and leg fragments have been discovered thus far.
References
- BBC - Dawn of Man (2000) by Robin Mckie| ISBN 0-7894-6262-1
- Template:Cite book
- Australopithecus afarensis from The Human Origins Program at the Smithsonian Institution
External links
- Lucy at the American Museum of Natural History in Manhattan
- Lucy at the Institute of Human Origins at Arizona State University
- http://www.geocities.com/palaeoanthropology/Aafarensis.html
- http://www.becominghuman.org/
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