Paranthropus (from Greek παρα, para "beside"; άνθρωπος, ánthropos "human") is a contested genus of extinct hominins that lived between 2.6 and 1.1 million years ago (mya). Also known as robust australopithecines, they were bipedal and probably descended from Australopithecus 2.7 mya. However, Paranthropus is sometimes considered synonymous with Australopithecus.
|Skull of P. boisei|
Paranthropus is characterised by robust skulls, with a prominent gorilla-like sagittal crests along the midline–which suggest strong chewing muscles–and broad, grinding herbivorous teeth. P. robustus was likely a generalist omnivore, whereas P. boisei seems to have specialized on grasses and sedges. Paranthropus likely were polygamous, but it is unknown if they lived in a harem or multi-male society. They could possibly be associated with tools and fire usage.
The genus Paranthropus was first erected by Scottish South African palaeontologist Robert Broom in 1938, with the type species P. robustus. The type specimen, a male braincase, TM 1517, was discovered by schoolboy Gert Terblanche at the Kromdraai fossil site, about 70 km (43 mi) southwest of Pretoria, South Africa. By 1988, at least 6 individuals were unearthed.
In 1948, at Swartkrans Cave, in about the same vicinity as Kromdraai, Broom and South African paleontologist John Talbot Robinson described P. crassidens based on a subadult jaw, SK 6. Many other Paranthropus specimens discovered earlier at Swartkrans were then placed into P. crassidens. However, this has since been synonymized with P. robustus.
In 1959, P. boisei was discovered by Mary Leakey at Olduvai Gorge, Tanzania (specimen OH 5). Her husband Louis named it Zinjanthropus boisei, deriving 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, and was subsumed into Paranthropus. Austrian anthropologist Raymond Dart made his now famous remark, "…what would have happened if [the A. africanus specimen] Mrs. Ples had met Dear Boy [OH 5] one dark night."
In 1951, American anthropologists Sherwood Washburn and Bruce D. Patterson were the first to suggest that Paranthropus should be considered a 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 echoing support, Leakey and Robinson continued defending its validity. In 1967, South African paleontologist Phillip V. Tobias considered Paranthropus to be a junior synonym of Australopithecus, but various other authors were unsure until more complete remains were found.
In 1985, Paraustralopithecus aethiopicus, first described by French paleontologists Camille Arambourg and Yves Coppens in 1968, was subsumed into Paranthropus as P. aethiopicus. It was originally based on a mandible with teeth from the Shungura Formation, Ethiopia (Omo 18), but was reclassified by after the discovery of the skull KNM WT 17000.
There is currently no clear consensus on the validity of Paranthropus. In 2004, evolutionary biologist Richard Dawkins noted "perhaps several different species" of robust australopithecines, and "as usual their affinities, and the exact number of species, are hotly disputed."
Paranthropus had a massively built skull, with a prominent gorilla-like sagittal crest on the midline of the skull which anchored massive temporalis muscles used in chewing. Most species had a brain about 40% the size of that of a modern human.
In comparison to the large, robust head, the body was rather petit. At Swartkrans Members 1 and 2, about 35% of the individuals are estimated to have weighed 28 kg (62 lb), 22% about 43 kg (95 lb) comparable to a human, and the remaining 43% less than 54 kg (119 lb). At Member 3, all individuals were about 45 kg (99 lb).
Paranthropus were bipeds, and their hips, legs, and feet resemble both its ancestor, Australopithecus afarensis, and modern humans. There was some size variation between the different species, but most stood roughly 1.3 to 1.4 m (4 ft 3 in to 4 ft 7 in) tall and were quite well muscled. The pelvis is similar to A. afarensis, but the hip joints are smaller in Paranthropus. The similar hip structure between A. afarensis and Paranthropus implies that they had a similar walking gait. However, their human-like big toe, well developed plantar aponeurosis, and more distal ankle joint show more support to the foot bones, and a human "toe-off" gait cycle.
Paranthropus seems to have had notably high rates of pitting enamel hypoplasia (PEH), where tooth enamel formation is spotty instead of mostly uniform. In P. robustus, about 47% of baby teeth and 14% of adult teeth were affected, in comparison to respectively 6.7% and 4.3% in any other hominin species. The condition of these holes covering the entire tooth is consistent with the human ailment amelogenesis imperfecta. However, since circular holes in enamel coverage are uniform in size, only present on the molar teeth, and have the same severity across individuals, the PEH may have been a genetic condition. It is possible that the coding-DNA concerned with thickening enamel also left them more vulnerable to PEH.
Diet seems to have ranged dramatically with location. The East African P. robustus appears to have been a generalist omnivore, with a diet similar to contemporaneous Homo and nearly identical to the later H. ergaster, and subsisted on mainly C4 savanna plants and C3 forest plants, which could indicate either seasonal shifts in diet or seasonal migration from forest to savanna. The South African P. boisei, on the other hand, was a specialist feeder on C4 grasses and sedges, much like modern geladas, likely competing with horses, pigs, hippos, and bovines for food in a very restricted wetland habitat. Paranthropus likely did not use its enhanced jaw muscles for cracking open nuts and seeds as was previously thought, and relied more on its molars than its incisors for eating compared to A. africanus.
Paranthropus is associated with stone tools in both southern and eastern Africa, although these tools are generally attributed to early Homo. However, hand fossils from the 1.5–1 Ma South African Swartkrans Cave indicate that the hand of P. robustus was adapted for precision grasping, which could indicate tool use. Tools would have been used to cut or process vegetation. Bones burnt to a temperature consistent with campfires were also associated with P. robustus, which could indicate some of the earliest fire usage.
Paranthropus had pronounced sexual dimorphism between males and females, which is commonly correlated with a male-dominated polygamous society. P. robustus may have had a harem society similar to modern forest-dwelling silverback gorillas, where one male has exclusive breeding rights to a group of females, as male-female size disparity is comparable to gorillas (based on facial dimensions), increased mortality in males may have occurred due to greater risk of predation in lone males, and P. robustus is thought to have experienced delayed maturity like gorillas. However, delayed maturity is typically characteristic of multi-male societies, and savanna baboons are known to live in multi-male societies to better protect the troop from predation in their more exposed environment.
Paranthropus are thought to have lived in wooded areas rather than the grasslands of Australopithecus. Paranthropus first appeared roughly 2.7 million years ago (mya), and Australopithecus had mostly disappeared by this time. Paranthropus is known to have coexisted with H. habilis, and possibly H. erectus.
The left foot of a P. boisei individual seems to have been bitten off by a crocodile, possibly Crocodylus anthropophagus, and another's leg shows evidence of leopard predation. Other likely predators of great apes include the hunting hyena Chasmaporthetes nitidula, and the saber-toothed cats Dinofelis and Megantereon.
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