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Australopithecus Boisei Ramsaday college Australopithecus boisei Paranthropus boisei or Australopithecus boisei was an early hominin, described as the largest of the Paranthropus genus (robust australopithecines). The word Paranthropus is based on the Greek words, ‘para’ meaning ‘beside’ or ‘near’ and ‘anthropus’ meaning ‘man’. It lived in Eastern Africa during the Pleistocene epoch from about 2.3 [discovered in Omo in Ethiopia] until about 1.2 million years ago. The largest skull specimen found of Paranthropus boisei is dated to 1.4 million years old, discovered at Konso in Ethiopia. Important fossil discoveries: • L 74 – a 2.3-million-year-old lower jaw discovered in Omo, Ethiopia. This fossil is the most massive example of a jaw from this species. • KNM-ER 729 – a lower jaw of a male discovered in East Turkana, Kenya • OH 5 – skull discovered in 1959 by Mary Leakey in Olduvai Gorge, Tanzania dated to 1.8 million years old, this is the ‘type specimen’ or official representative of this species. It was originally classified as Zinjanthropus boisei and earned the nickname ‘Nutcracker Man’ because of its powerful jaws and large teeth. Layers of volcanic sediment around this skull have enabled the reliable dating of this fossil. • KNM-ER 732 – a 1.7-million-year-old skull discovered in 1970 by Richard Leakey in Koobi Fora, East Turkana, Kenya. Compared with a male’s skull, this female has a smaller face and no sagittal crest along the top of the braincase. Distribution: Fossils of Paranthropus boisei have been found in the countries of Ethiopia, Kenya and Tanzania in east Africa. Key physical features: A. boisei had typical physical characteristics - a relatively small body and a ‘robust’ or strongly built skull including large lower jaws with extremely large molar teeth. Body size and shape • lack of skeletal evidence makes reconstructing the exact sizes difficult. P. boisei were probably only slightly larger than Australopithecus africanus. • males were significantly larger than females • rib cage was cone-shaped like those of apes rather than the barrel-shape of human rib-cages. Brain • size was relatively small and ranged from 420 cubic centimetres for P. walkeri to 520 cubic centimetres for P. boisei and P. robustus. Skull Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college • cranial features were ape-like with a flat forehead and a prominent brow ridge above the eyes. • the face was relatively broad with flaring cheekbones. P. walkeri had a more projecting face than the other species in this genus, which had shorter, flatter faces. • spinal cord passed through the centre of the skull base, indicating these species walked upright. • males had a massive bony ridge running along the top of the skull, called a sagittal crest. This acted as an anchor for their powerful jaw muscles. Jaws and teeth • front teeth (incisors and canines) were very small compared with the extremely large molar teeth. The molar teeth were very effective for crushing and grinding tough plant foods • jaws were large and robust for the attachment of powerful chewing muscles Limbs and pelvis • legs had human-like features that indicate an ability to walk upright • arms were long compared with the legs • pelvis was similar to that of Australopithecus as it was built for walking on two legs but without the refinements for the striding gait of humans. Phylogeny: P. boisei is usually thought to descend from earlier P. aethiopicus (who inhabited the same geographic area just a few hundred thousand years before) and lived alongside several other species of early humans during its 1.1 million years existence. P. boisei belongs to just one of the many side branches of human evolution, which most scientists agree includes all Paranthropus species and did not lead to H. sapiens. Support for P. boisei being descended from A. aethiopicus has steadily increased. However, some still group P. boisei as a sister species of P. robustus and believe that they descended from A. africanus. The two more derived forms share a molar trait with A. africanus, in that the second molar (M2) is larger than the third (M3). Members of the latter group, such as Henry McHenry, contend that the more primitive A. aethiopicus is an example of homoplasy or convergent evolution, making the robust traits homoplasies. Paleoanthropologists have tended to be conservative in their acceptance of homoplasies; common ancestry is more parsimonious. The 1975 discovery of P. boisei specimen KNM-ER 406 and H. erectus specimen KNM- ER 3733 in the same stratigraphic layer was the first example of species coexistence. This discovery cleared up a long time controversy and confirmed that more than one species of early humans lived in the same geographical area at the same time. More finds have confirmed that this species was one of the most prevalent in Eastern Africa Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology Ramsaday college during the time period when early members of the genus Homo were also present. This replaced the traditional view of a single human lineage by the notion of a human family tree with many branches (like most other family trees); we’ve been adding branches though discoveries of new species ever since. Except for the possible A. aethiopicus → P. boisei scenario, the robust australopiths were evolutionary dead-ends as far as we know. Conclusions: Australopithecus boisei is an important species both in the history of paleoanthropological research and in constructing the phylogeny of the hominid lines. The features it shares or lacks with contemporary and earlier species makes relatively clear the relative phylogeny of the “robust” australopithecines. It also is present at a time when stone tools become much more common, and may have even made and used some. In the end, however, it seems that boisei became too specialized, and died with climatic and/or environmental shifts. Sk. Hedayet Hossain, Assistant Professor, Department of Anthropology .
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