Paranthropus

''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: '' P. robustus'' and '' P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be synonymous with ''Australopithecus''. They are also referred to as the robust australopithecines. They lived between approximately 2.9 and 1.2 million years ago (mya) from the end of the Pliocene.

''Paranthropus'' is characterised by robust skulls, with a prominent gorilla-like sagittal crest along the midline—which suggest strong chewing muscles—and broad, herbivorous teeth used for grinding. However, they likely preferred soft food over tough and hard food. Typically, ''Paranthropus'' species were generalist feeders, but while ''P. robustus'' was likely an omnivore, ''P. boisei'' seems to have been herbivorous, possibly preferring abundant bulbotubers. Paranthropoids were bipeds. Despite their robust heads, they had comparatively small bodies. Average weight and height are estimated to be at for ''P. robustus'' males, at for ''P. boisei'' males, at for ''P. robustus'' females, and at for ''P. boisei'' females.

They were possibly polygamous and patrilocal, but there are no modern analogues for australopithecine societies. They are associated with bone tools and contested as the earliest evidence of fire usage. They typically inhabited woodlands, and coexisted with some early human species, namely '' A. africanus'', '' H. habilis'' and '' H. erectus''. They were preyed upon by the large carnivores of the time, specifically crocodiles, leopards, sabertoothed cats and hyenas.

Taxonomy

Species

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''P. robustus''

The genus ''Paranthropus'' was first erected by Scottish-South African palaeontologist Robert Broom in 1938, with the type species '' P. robustus''. "''Paranthropus''" derives from Ancient Greek παρα ''para'' beside or alongside; and άνθρωπος ''ánthropos'' man. The type specimen, a male braincase, TM 1517, was discovered by schoolboy Gert Terblanche at the Kromdraai fossil site, about southwest of Pretoria, South Africa. By 1988, at least six individuals were unearthed in around the same area, now known as the Cradle of Humankind.

In 1948, at Swartkrans Cave, in about the same vicinity as Kromdraai, Broom and South African palaeontologist John Talbot Robinson described ''P. crassidens'' based on a subadult jaw, SK 6. He believed later ''Paranthropus'' were morphologically distinct from earlier ''Paranthropus'' in the cave—that is, the Swartkrans ''Paranthropus'' were reproductively isolated from Kromdraai ''Paranthropus'' and the former eventually speciated. By 1988, several specimens from Swartkrans had been placed into ''P. crassidens''. However, this has since been synonymised with ''P. robustus'' as the two populations do not seem to be very distinct.

''P. boisei''

In 1959, '' P. boisei'' was discovered by Mary Leakey at Olduvai Gorge, Tanzania (specimen OH 5). Her husband Louis named it ''Zinjanthropus boisei'' because he believed it differed greatly from ''Paranthropus'' and ''Australopithecus''. The name derives from " Zinj", an ancient Arabic word for the coast of East Africa, and "boisei", referring to their financial benefactor Charles Watson Boise. However, this genus was rejected at Mr. Leakey's presentation before the 4th Pan-African Congress on Prehistory, as it was based on a single specimen. The discovery of the Peninj Mandible made the Leakeys reclassify their species as ''Australopithecus (Zinjanthropus) boisei'' in 1964, but in 1967, South African palaeoanthropologist Phillip V. Tobias subsumed it into ''Australopithecus'' as ''A. boisei''. However, as more specimens were found, the combination ''Paranthropus boisei'' became more popular.

It is debated whether the wide range of variation in jaw size indicates simply sexual dimorphism or a grounds for identifying a new species. It could be explained as groundmass filling in cracks naturally formed after death, inflating the perceived size of the bone. ''P. boisei'' also has a notably wide range of variation in skull anatomy, but these features likely have no taxonomic bearing.

''P. aethiopicus''

In 1968, French palaeontologists Camille Arambourg and Yves Coppens described "''Paraustralopithecus aethiopicus''" based on a toothless mandible from the Shungura Formation, Ethiopia (Omo 18). In 1976, American anthropologist Francis Clark Howell and Breton anthropologist Yves Coppens reclassified it as ''A. africanus''. In 1986, after the discovery of the skull KNM WT 17000 by English anthropologist Alan Walker and Richard Leakey classified it into ''Paranthropus'' as '' P. aethiopicus''. There is debate whether this is synonymous with ''P. boisei'', the main argument for separation being the skull seems less adapted for chewing tough vegetation.

In 1989, palaeoartist and zoologist Walter Ferguson reclassified KNM WT 17000 into a new species, ''walkeri'', because he considered the skull's species designation questionable as it comprised the skull whereas the holotype of ''P. aethiopicus'' comprised only the mandible. Ferguson's classification is almost universally ignored, and is considered to be synonymous with ''P. aethiopicus''.

Others

In 2015, Ethiopian palaeoanthropologist Yohannes Haile-Selassie and colleagues described the 3.5–3.2 Ma '' A. deyiremeda'' based on three jawbones from the Afar Region, Ethiopia. They noted that, though it shares many similarities with ''Paranthropus'', it may not have been closely related because it lacked enlarged molars which characterize the genus. Nonetheless, in 2018, independent researcher Johan Nygren recommended moving it to ''Paranthropus'' based on dental and presumed dietary similarity.

Validity

In 1951, American anthropologists Sherwood Washburn and Bruce D. Patterson were the first to suggest that ''Paranthropus'' should be considered a junior synonym of ''Australopithecus'' as the former was only known from fragmentary remains at the time, and dental differences were too minute to serve as justification. In face of calls for subsumation, Leakey and Robinson continued defending its validity. Various other authors were still unsure until more complete remains were found. ''Paranthropus'' is sometimes classified as a subgenus of ''Australopithecus''.

There is currently no clear consensus on the validity of ''Paranthropus''. The argument rests upon whether the genus is monophyletic—is composed of a common ancestor and all of its descendants—and the argument against monophyly (that the genus is paraphyletic) says that ''P. robustus'' and ''P. boisei'' evolved similar gorilla-like heads independently of each other by coincidence (convergent evolution), as chewing adaptations in hominins evolve very rapidly and multiple times at various points in the family tree ( homoplasy). In 1999, a chimp-like ulna forearm bone was assigned to ''P. boisei'', the first discovered ulna of the species, which was markedly different from ''P. robustus'' ulnae, which could suggest paraphyly.

Evolution

''P. aethiopicus'' is the earliest member of the genus, with the oldest remains, from the Ethiopian Omo Kibish Formation, dated to 2.6 mya at the end of the Pliocene

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