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General overview Australopithecus robustus and Australopithecus boisei are species of Australopithecus which the encyclopedia of brittanica classify as an extinct genus of the hominid family found in Africa between about 4 and 1 million years ago.At least seven species of australopithecines are now generally recognized, including Australopithecus afarensis, A. africanus, A. bahrelghazali, A. anamensis, A. boisei, A. robustus, and A. aethiopicus. Among their many shared anatomical traits were a fully erect posture and bipedal gait. The most “primitive” anatomical feature was a small and apelike braincase, comparable in size to those of gorillas and chimpanzees when measured relative to overall body size. More species which could be classified as Australopithecus have been reported found, including A. garhi in Ethiopia in 1999. There is considerable disagreement among experts on the number of species that should be included within the genus, and two of the seven species listed above—A. bahrelghazali and A. anamensis—are based on very fragmentary remains. Two well-known australopithecines, A. boisei (from E Africa) and A. robustus (from S Africa), featured very large molars and premolars, very thick jaws, and craniums topped by prominent crests.these two are the species which I will be focusing on furthur in the report. The features listed above probably reflect a relatively specialized diet of rough vegetable matter. In contrast, A. afarensis and A. africanus had cranio-dental features consistent with a more generalized diet. The large-toothed australopithecines also had skeletons indicative of a heavier build than the small-toothed australopithecines; the former are believed to have weighed 25 to 50 lb (10 to 20 kg) more than the latter, even though they were approximately the same height. Based on these pronounced differences, australopithecines are classified into two distinct types: gracile and robust. The robust australopithecines all became extinct between 1.5 and 1 million years ago, while one of the gracile autralophithecines is believed to have given rise to the branch leading to the emergence of the genus Homo c.2.5 million years ago. When the fossil record was still poorly understood, it was thought that there existed two distinct branches of early human. These were the "gracile", meaning small, and "robust", meaning large, forms of the genus Australopithecus. The gracile forms were represented by the species A. afarensis and A. africanus; the robust forms by the species A. robustus and A. boisei. The word "robust" originally referred to the larger body that the members of these two species were supposed, by paleoanthropologists, to have had. Few postcranial bones existed at the time for either, and inferences were based on the size of their teeth. Now that there are more fossils from which to draw our conclusions, it is apparent that the average body size was not significantly different between any of the species. But the term does accurately reflect the difference in the size of the cheek teeth (molars and premolars) of these species. All of these species had been assigned to the genus Australopithecus. Yet, because of the extreme heavy chewing adaptations of the "robust" forms, it is thought that they represent a group of species (or clade) separate from that which led to modern humans, and eventually this clade became extinct. As such, many researchers believe that they should be placed in their own genus Paranthropus, separate from the australopiths that gave rise to later humans. This is not universally accepted by researchers, although we use that designation for our presentation of the human lineage. This division would place all of the robust forms together, with the early P. aethiopicus species as the probable ancestor to both later robust species, P. robustus in southern Africa and P. boisei in eastern Africa. There is no consensus among the experts concerning the evolutionary relationship among the various australopithecines, or between the australopithecines and Homo habilis, which is considered by many to be the earliest species of the genus Homo. One proposal is that A. afarensis gave rise to two distinct lineages c.3 million years ago: One branch became the robust australopithecines (doomed to extinction), while the other branch became the gracile species (one species of which eventually evolved into H. habilis). Many researchers believe that the species that evolved into H. habilis was A. africanus. Other experts reject this model, as well as the claim that A. africanus played any such key role. Increasingly, specialists favor assigning the robust australopithecines to a completely seperate genus, Paranthropus, because of the very significant physical differences between the robust and gracile species. According to this view, A. afarensis was the last common ancestor of these two distinct types of hominids. However, some researchers suggest, based on subtle facial features, that the eastern African forms P. aethiopicus and P. boisei form a lineage separate from the South African species P. robustus. In this case, P. robustus would descend from the southern gracile A. africanus, and the genus name Paranthropus would be invalid. This implies that the evolution of similar heavy chewing complexes occurred twice independently. There is still much debate as to the exact ancestor/descendent relationship among the robust species. As such, some species are referred to in the literature by more than one name. As more fossils are found, our understanding of this branch of the human family tree will hopefully become clearer. 1930s, the first robust australopithecine was found by Robert Broom . He found specimens of early hominid fossils that were simply built too heavily for them to be of the same type as A. africanus. Therefore, he grouped them together and gave them a new species name – Australopithecus robustus. There is still however a lively debate over the genus name and this species is also often referred to as Paranthropus robustus. A common perception is that the robust species of australopithecine differs sufficiently from the gracile type to warrant a different genus name. In 1959, Mary Leakey made the first hominine discovery in East Africa at the Olduvai Gorge in Tanzania which resembled the robust australopithecines already found in South Africa. After reconstructing the skull which was built up out of hundreds of fragments, it was found that this specimen was even more "robust" than its southern relatives. At first, it was named Zinjanthropus boisei, but later changed to Australopithecus boisei. There is still however a lively debate over the genus name and this species is also often referred to as Paranthropus boisei.Again a common perception is that the robust species of australopithecine differs sufficiently from the gracile type to warrant a different genus name.
Approximate Word count = 4301
Approximate Pages = 17.2
(250 words per page double spaced)
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