Paranthropus boisei

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Paranthropus boisei
Temporal range:
Ma
↓
Reconstruction of the
OH 5
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Genus: †Paranthropus
Species:
†P. boisei
Binomial name
†Paranthropus boisei
(Louis Leakey, 1959)
Synonyms
  • Zinjanthropus boisei
  • Australopithecus boisei
  • P. aethiopicus
    ?

Paranthropus boisei is a

holotype specimen, OH 5, was discovered by palaeoanthropologist Mary Leakey in 1959 at Olduvai Gorge, Tanzania and described by her husband Louis a month later. It was originally placed into its own genus as "Zinjanthropus boisei", but is now relegated to Paranthropus along with other robust australopithecines. However, it is also argued that Paranthropus is an invalid grouping and synonymous with Australopithecus
, so the species is also often classified as Australopithecus boisei.

Robust australopithecines are characterised by heavily built skulls capable of producing high

arboreal
to a degree.

P. boisei was originally believed to have been a

H. ergaster/erectus. These were likely preyed upon by the large carnivores of the time, including big cats, crocodiles and hyenas
.

Research history

"OH 5" redirects here. For the Ohio congressional district, see
OH-5
.
Map of Paranthropus finds (P. boisei in red)

Discovery

Palaeoanthropologists

molar tooth in Olduvai Gorge, catalogue ID Olduvai Hominin (OH) 3.[3]

On the morning of July 17, 1959, Louis felt ill and stayed at camp while Mary went out to Bed I's Frida Leakey Gully.[4] Sometime around 11:00 AM, she noticed what appeared to be a portion of a skull poking out of the ground, OH 5.[5] The dig team created a pile of stones around the exposed portion to protect it from further weathering.[6] Active excavation began the following day; they had chosen to wait for photographer Des Bartlett to document the entire process.[6] The partial cranium was fully unearthed August 6, though it had to be reconstructed from its fragments which were scattered in the scree.[7] Louis published a short summary of the find and context the following week.[8]

Louis determined OH 5 to be a subadult or adolescent based on dental development, and he and Mary nicknamed it "Dear Boy".[9] After they reconstructed the skull and jaws, newspapers began referring to it as "Nutcracker Man" due to the large back teeth and jaws which gave it a resemblance to vintage nutcrackers.[10] South African palaeoanthropologist Phillip Tobias, a colleague of the Leakeys, has also received attribution for this nickname.[11] The cranium was taken to Kenya after its discovery and was there until January 1965 when it was placed on display in the Hall of Man at the National Museum of Tanzania in Dar es Salaam.[12]

Other specimens

Louis preliminarily supposed OH 5 was about half a million years old, but in 1965, American geologists

potassium–argon dating of anortoclase crystals from an overlying tuff (volcanic ash) bed.[13] Such an application of geochronology was unprecedented at the time.[14]

Various P. boisei specimens

The first identified jawbone,

Peninj 1, was discovered Lake Natron just north of Olduvai Gorge in 1964.[15]: 107 [16][17] Especially from 1966 to 1975, several more specimens revealing facial elements were reported from the Shungura Formation, Ethiopia; Koobi Fora and Chesowanja, Kenya; and Omo and Konso, Ethiopia. Among the notable specimens found include the well preserved skull KNM-ER 406 from Koobi Fora in 1970.[15]: 108–109  In 1997, the first specimen with both the skull and jawbone (and also one of the largest specimens), KGA10-525, was discovered in Konso.[18] In 1999, a jawbone was recovered from Malema, Malawi, extending the species' southernmost range over 2,000 km (1,200 mi) from Olduvai Gorge.[15]: 109  The first definitive bodily elements of P. boisei associated with facial elements, OH 80 (isolated teeth with an arm and a leg), were discovered in 2013. Previously, body remains lacking unambiguous diagnostic skull elements had been dubiously assigned to the species, namely the partial skeleton KNM-ER 1500 associated with a small jawbone fragment.[19] In 2015, based on OH 80, American palaeoanthropologist Michael Lague recommended assigning the isolated humerus specimens KNM-ER 739, 1504, 6020 and 1591 from Koobi Fora to P. boisei.[20] In 2020, the first associated hand bones were reported, KNM-ER 47000 (which also includes a nearly complete arm), from Ileret, Kenya.[21]

Naming

The remains were clearly australopithecine (not of the genus Homo), and at the time, the only australopithecine genera described were Australopithecus by Raymond Dart and Paranthropus (the South African P. robustus) by Robert Broom, and there were arguments that Paranthropus was synonymous with Australopithecus. Louis believed the skull had a mix of traits from both genera, briefly listing 20 differences, and so used OH 5 as the basis for the new genus and species "Zinjanthropus boisei" on August 15, 1959. The genus name derives from the medieval term for East Africa, "Zanj", and the specific name was in honour of Charles Watson Boise, the Leakeys' benefactor.[22] He initially considered the name "Titanohomo mirabilis" ("wonderful Titan-like man").[23]

Soon after, Louis presented "Z." boisei to the 4th Pan-African Congress on Prehistory in Léopoldville,

Phillip V. Tobias gave a far more detailed description of OH 5 in a monograph (edited by Louis). Tobias and Louis still retained "Zinjanthropus", but recommended demoting it to subgenus level as Australopithecus ("Zinjanthropus") boisei, considering Paranthropus to be synonymous with Australopithecus.[3] Synonymising Paranthropus with Australopithecus was first suggested by anthropologists Sherwood Washburn and Bruce D. Patterson in 1951, who recommended limiting hominin genera to only Australopithecus and Homo.[26]

Classification

The genus Paranthropus (otherwise known as "robust australopithecines") typically includes P. boisei, P. aethiopicus and P. robustus. It is debated if Paranthropus is a valid natural grouping (

paraphyletic). Because skeletal elements are so limited in these species, their affinities with each other and to other australopithecines is difficult to gauge with accuracy. The jaws are the main argument for monophyly, but such anatomy is strongly influenced by diet and environment, and could in all likelihood have evolved independently in P. boisei and P. robustus. Proponents of monophyly consider P. aethiopicus to be ancestral to the other two species, or closely related to the ancestor. Proponents of paraphyly allocate these three species to the genus Australopithecus as A. boisei, A. aethiopicus and A. robustus.[15]
: 117–121 

Before P. boisei was described (and P. robustus was the only member of Paranthropus), Broom and Robinson continued arguing that P. robustus and A. africanus (the then only known australopithecines) were two distinct lineages. However, remains were not firmly dated, and it was debated if there were indeed multiple hominin lineages or if there was only 1 leading to humans. In 1975, the P. boisei skull KNM-ER 406 was demonstrated to have been contemporaneous with the

A. afarensis from East Africa, anthropologists Donald Johanson and Tim D. White suggested that A. afarensis was instead the last common ancestor between Homo and Paranthropus, and A. africanus was the earliest member of the Paranthropus lineage or at least was ancestral to P. robustus, because A. africanus inhabited South Africa before P. robustus, and A. afarensis was at the time the oldest-known hominin species at roughly 3.5 million years old.[27] Now, the earliest known South African australopithecine ("Little Foot") dates to 3.67 million years ago, contemporaneous with A. afarensis.[28]

Such arguments are based on how one draws the hominin family tree, and the exact classification of Australopithecus species with each other is quite contentious. For example, if the South African

A. garhi as the ancestor of P. aethiopicus instead of A. africanus (assuming Paranthropus is monophyletic, and that P. aethiopicus evolved at a time in East Africa when only A. garhi existed there).[29]

Monophyly[15]: 119 

A. africanus

P. aethiopicus

P. boisei

P. robustus

Paraphyly[15]: 119 

P. aethiopicus

P. boisei

Monophyly[29]
A. africanus

A. garhi

P. aethiopicus

P. boisei

P. robustus

Three example family trees with P. boisei (note, they are not absolute)

Because P. boisei and P. aethiopicus are both known from East Africa and P. aethiopicus is only confidently identified from the skull

sensu stricto ("in the strict sense") can be used to respectively include and exclude P. aethiopicus from P. boisei when discussing the lineage as a whole.[15]
: 106–107 

African
hominin timeline (in mya)
View references
H. sapiensH. nalediH. rhodesiensisH. ergasterAu. sedibaP. robustusP. boiseiH. rudolfensisH. habilisAu. garhiP. aethiopicusLD 350-1K. platyopsAu. bahrelghazaliAu. deyiremedaAu. africanusAu. afarensisAu. anamensisAr. ramidusAr. kadabba


P. aethiopicus is the earliest member of the genus, with the oldest remains, from the Ethiopian Omo Kibish Formation, dated to 2.6 million years ago (mya) at the end of the Pliocene.[30] It is possible that P. aethiopicus evolved even earlier, up to 3.3 mya, on the expansive Kenyan floodplains of the time.[31] The oldest P. boisei remains date to about 2.3 mya from Malema.[30] The youngest record of P. boisei comes Olduvai Gorge (OH 80) about 1.34 mya;[19] however, due a large gap in the hominin fossil record, P. boisei may have persisted until 1 mya.[15]: 109  P. boisei changed remarkably little over its nearly one-million-year existence.[32]

Anatomy

Skull

Reconstruction of P. boisei by Cicero Moraes

P. boisei is the most robust of the robust australopithecines, whereas the South African P. robustus is smaller with comparatively more gracile features.

bite force.[33]

The

bunodont, featuring low and rounded cusps. The premolars resemble molars (are molarised), which may indicate P. boisei required an extended chewing surface for processing a lot of food at the same time. The enamel on the cheek teeth are among the thickest of any known ape, which would help resist high stresses while biting.[33]
: 128–132 

Peninj 1 showing postcanine megadontia

Brain and sinuses

In a sample of 10 P. boisei specimens, brain size varied from 444–545 cc (27.1–33.3 cu in) with an average of 487.5 cc (29.75 cu in).[36] However, the lower-end specimen, Omo L338‐y6, is a juvenile, and many skull specimens have a highly damaged or missing frontal bone which can alter brain volume estimates.[37] The brain volume of australopithecines generally ranged from 400–500 cc (24–31 cu in), and for contemporary Homo 500–900 cc (31–55 cu in).[38]

Regarding the

transverse and sigmoid sinuses. In 1988, Falk and Tobias demonstrated that hominins can have both an occipital/marginal and transverse/sigmoid systems concurrently or on opposite halves of the skull, such as with the P. boisei specimen KNM-ER 23000.[39]

Smithsonian National Museum of Natural History

In 1983, French anthropologist Roger Saban stated that the parietal branch of the middle meningeal artery originated from the posterior branch in P. boisei and P. robustus instead of the anterior branch as in earlier hominins, and considered this a derived characteristic due to increased brain capacity.[40] It has since been demonstrated that the parietal branch could originate from either the anterior or posterior branches, sometimes both in a single specimen on opposite sides of the skull as in KNM-ER 23000 and OH 5.[41]

Postcranium

The wide range of size variation in skull specimens seems to indicate a great degree of

H. habilis.[15]
: 116 

femoral shaft (left) and radius
(right)
Scale bar=1 cm (0.39 in)

Instead, the OH 80 femur, more like

precision grip like Homo, the hand was still dextrous enough to handle and manufacture simple tools.[21]

Palaeobiology

Diet

In 1954, Robinson suggested that the heavily built skull of Paranthropus (at the time only including P. robustus) was indicative of a specialist diet specifically adapted for processing a narrow band of foods. Because of this, the predominant model of Paranthropus extinction for the latter half of the 20th century was that it was unable to adapt to the volatile climate of the Pleistocene, unlike the much more adaptable Homo.[33] It was also once thought P. boisei cracked open nuts and similar hard foods with its powerful teeth, giving OH 5 the nickname "Nutcracker Man".[44]

However, in 1981, English anthropologist

frugivorous) mandrills, chimpanzees and orangutans.[45] The microwearing on P. boisei molars is different from that on P. robustus molars, and indicates that P. boisei, unlike P. robustus, very rarely ever ate hard foods. Carbon isotope analyses report a diet of predominantly C4 plants, such as low quality and abrasive grasses and sedges.[46][47][48] Thick enamel is consistent with grinding abrasive foods.[33] The microwear patterns in P. robustus have been thoroughly examined, and suggest that the heavy build of the skull was only relevant when eating less desirable fallback foods. A similar scheme may have been in use by P. boisei.[33] Such a strategy is similar to that used by modern gorillas, which can sustain themselves entirely on lower quality fallback foods year-round, as opposed to lighter built chimps (and presumably gracile australopithecines) which require steady access to high quality foods.[49]

Reconstruction of MGL 95211 skull and jaw

In 1980, anthropologists Tom Hatley and John Kappelman suggested that early hominins (convergently with bears and pigs) adapted to eating abrasive and calorie-rich underground storage organs (USOs), such as roots and tubers.[50] Since then, hominin exploitation of USOs has gained more support. In 2005, biological anthropologists Greg Laden and Richard Wrangham proposed that Paranthropus relied on USOs as a fallback or possibly primary food source, and noted that there may be a correlation between high USO abundance and hominin occupation.[49] In this model, P. boisei may have been a generalist feeder with a predilection for USOs,[51][48] and may have gone extinct due to an aridity trend and a resultant decline in USOs in tandem with increasing competition with baboons and Homo.[52] Like modern chimps and baboons, australopithecines likely foraged for food in the cooler morning and evening instead of in the heat of the day.[53]

Technology

By the time OH 5 was discovered, the Leakeys had spent 24 years excavating the area for early hominin remains, but had instead recovered mainly other animal remains as well as the Oldowan stone tool industry.[3] Because OH 5 was associated with the tools and processed animal bones, they presumed it was the toolmaker. Attribution of the tools was promptly switched to the bigger-brained H. habilis upon its description in 1964.[3] In 2013, OH 80 was found associated with a mass of Oldowan stone tools and animal bones bearing evidence of butchery. This could potentially indicate P. boisei was manufacturing this industry and ate meat to some degree.[19]

Additionally, the

Early Stone Age of Africa coincides with simple bone tools. In South Africa, these are unearthed in the Cradle of Humankind and are largely attributed to P. robustus. In East Africa, a few have been encountered at Olduvai Gorge Beds I–IV, occurring over roughly 1.7 to 0.8 million years ago, and are usually made of limb bones and possibly teeth of large mammals, most notably elephants. The infrequency of such large animals at this site may explain the relative rarity of bone tools. The toolmakers were modifying bone in much the same way as they did with stone. Though the Olduvan bone tools are normally ascribed to H. ergaster/erectus, the presence of both P. boisei and H. habilis obfuscates attribution.[54]

Social structure

In 1979, American biological anthropologist Noel T. Boaz noticed that the relative proportions between large mammal families at the Shungura Formation are quite similar to the proportion in modern-day across sub-Saharan Africa. Boaz believed that hominins would have had about the same population density as other large mammals, which would equate to 0.006–1.7 individuals per square kilometre (0.4 square mile). Alternatively, by multiplying the density of either bovids, elephants, or hippos by the percentage of hominin remains out of total mammal remains found at the formation, Boaz estimated a density of 0.001–2.58 individuals per square kilometre.[55] Biologist Robert A. Martin considered population models based on the number of known specimens to be flimsy. In 1981, Martin applied equations formulated by ecologists Alton S. Harestad and Fred L. Bunnel in 1979 to estimate the home range and population density of large mammals based on weight and diet, and, using a weight of 52.4 kg (116 lb), he got: 130 ha (320 acres) and 0.769 individual per square kilometre if herbivorous; 1,295 ha (3,200 acres) and 0.077 individual if omnivorous; and 287,819 ha (711,220 acres) and 0.0004 individual if carnivorous. For comparison, he calculated 953 ha (2,350 acres) and 0.104 individual per square kilometre for omnivorous, 37.5-kilogram (83 lb) chimps.[56]

Male (left) and female (right) western gorilla skulls

A 2017 study postulated that, because male non-human

gluteus muscles) in male western lowland gorillas has been correlated with reproductive success. They extended their interpretation of the crest to the males of Paranthropus species, with the crest and resultantly larger head (at least in P. boisei) being used for some kind of display. This contrasts with other primates which flash the typically engorged canines in agonistic display (the canines of Paranthropus are comparatively small). However, it is also possible that male gorillas and orangutans require larger temporalis muscles to achieve a wider gape to better display the canines.[57]

Development

Australopithecines are generally considered to have had a faster,

tooth root is about 5 mm (0.20 in), which is similar to most other hominins at this stage. In contrast, the root of the P. robustus specimen SK 62 was 6 mm (0.24 in) when emerging through the dental alveolus (an earlier stage of development than gum emergence), so, unless either specimen is abnormal, P. robustus may have had a higher tooth-root formation rate. The specimen's 1st molar may have erupted 2–3 months before death, so possibly at 2.7–3.3 years of age. In modern apes (including humans), dental development trajectory is strongly correlated with life history and overall growth rate, but it is possible that early hominins simply had a faster dental trajectory and slower life history due to environmental factors, such as early weaning age exhibited in modern indriid lemurs.[58]

Palaeoecology

P. boisei remains have been found predominantly in what were wet, wooded environments, such as wetlands along lakes and rivers, wooded or arid shrublands, and semi-arid woodlands,[48] with the exception of the savanna-dominated Malawian Chiwondo Beds.[59] Its abundance likely increased during precession-driven periods of relative humidity while being more rare during intervals of aridity.[60] During the Pleistocene, there seems to have been coastal and montane forests in Eastern Africa. More expansive river valleys–namely the Omo River Valley–may have served as important refuges for forest-dwelling creatures. Being cut off from the forests of Central Africa by a savanna corridor, these East African forests would have promoted high rates of endemism, especially during times of climatic volatility.[61] Australopithecines and early Homo likely preferred cooler conditions than later Homo, as there are no australopithecine sites that were below 1,000 m (3,300 ft) in elevation at the time of deposition. This would mean that, like chimps, they often inhabited areas with an average diurnal temperature of 25 °C (77 °F), dropping to 10 or 5 °C (50 or 41 °F) at night.[53]

P. boisei coexisted with H. habilis,

sabertoothed cats Dinofelis and Megantereon,[66] and the crocodile Crocodylus anthropophagus.[67]

See also

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Bibliography

External links

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