species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
robust
Robustness is the property of being strong and healthy in constitution. When it is transposed into a system, it refers to the ability of tolerating perturbations that might affect the system’s functional body. In the same line ''robustness'' ca ...
australopithecine
Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally ''Australopithecus'' (cladistically including the genus, genera ''Homo'', ''Paranthropus'', and ''Kenyanthropus''), and it typically in ...
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
, about 2.27 to 0.87 (or, more conservatively, 2 to 1) million years ago. It has been identified in
Kromdraai
Kromdraai Conservancy is a protected conservation park located to the south-west of Gauteng province in north-east South Africa. It is in the Muldersdrift area not far from Krugersdorp.
Etymology
Its name is derived from Afrikaans meaning "Cro ...
,
Swartkrans
Swartkrans is a fossil-bearing cave designated as a South African National Heritage Site, located about from Johannesburg. It is located in the Cradle of Humankind World Heritage Site and is notable for being extremely rich in archaeological m ...
Gondolin
In Tolkien's legendarium, Gondolin was a secret city of Elves in the First Age of Middle-earth. The story of the Fall of Gondolin tells of the founding of the city; of the arrival there of Tuor, a prince of Men; of the betrayal of the city to Mor ...
Drimolen
The Drimolen Palaeocave System consists of a series of terminal Pliocene to early Pleistocene hominin-bearing palaeocave fills located around north of Johannesburg, South Africa, and about north of Sterkfontein in the UNESCO World Heritage Site ...
Caves. Discovered in 1938, it was among the first early
hominin
The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos) and in standard usage excludes the genus ''Gorilla'' (gorillas).
The t ...
s described, and became the
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
for the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''
Paranthropus
''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: ''Paranthropus robustus, P. robustus'' and ''P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be sy ...
''. However, it has been argued by some that ''Paranthropus'' is an invalid grouping and
synonymous
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
with ''
Australopithecus
''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Australopi ...
'', so the species is also often classified as ''Australopithecus robustus''.
Robust australopithecines—as opposed to gracile australopithecines—are characterised by heavily built skulls capable of producing high stresses and
bite force
Bite force quotient (BFQ) is a numerical value commonly used to represent the bite force of an animal, while also taking factors like the animal's size into account.
The BFQ is calculated as the regression of the quotient
In arithmetic, a ...
molars
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
and
premolar
The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...
s). Males had more heavily built skulls than females. ''P. robustus'' may have had a
genetic susceptibility
Public health genomics is the use of genomics information to benefit public health. This is visualized as more effective preventive care and disease treatments with better Specificity (statistics), specificity, tailored to the genetic makeup of ea ...
cavity
Cavity may refer to:
Biology and healthcare
*Body cavity, a fluid-filled space in many animals where organs typically develop
**Gastrovascular cavity, the primary organ of digestion and circulation in cnidarians and flatworms
*Dental cavity or too ...
rate similar to non-agricultural modern humans. The species is thought to have exhibited marked
sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
, with males substantially larger and more robust than females. Based on 3 specimens, males may have been tall and females . Based on 4 specimens, males averaged in weight and females . The brain volume of the specimen SK 1585 is estimated to have been 476 cc, and of DNH 155 about 450 cc (for comparison, the brain volume of contemporary ''
Homo
''Homo'' () is the genus that emerged in the (otherwise extinct) genus ''Australopithecus'' that encompasses the extant species ''Homo sapiens'' ( modern humans), plus several extinct species classified as either ancestral to or closely relate ...
'' varied from 500 to 900 cc). ''P. robustus'' limb anatomy is similar to that of other australopithecines, which may indicate a less efficient walking ability than modern humans, and perhaps some degree of
arboreality
Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose num ...
(movement in the trees).
''P. robustus'' seems to have consumed a high proportion of C4 savanna plants. In addition, it may have also eaten fruits, underground
storage organ
A storage organ is a part of a plant specifically modified for storage of energy
(generally in the form of carbohydrates) or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have ...
s (such as roots and tubers), and perhaps
honey
Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...
and
termite
Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blattode ...
s. ''P. robustus'' may have used bones as tools to extract and process food. It is unclear if ''P. robustus'' lived in a
harem
Harem (Persian: حرمسرا ''haramsarā'', ar, حَرِيمٌ ''ḥarīm'', "a sacred inviolable place; harem; female members of the family") refers to domestic spaces that are reserved for the women of the house in a Muslim family. A hare ...
society like
gorilla
Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s or a multi-male society like
baboon
Baboons are primates comprising the genus ''Papio'', one of the 23 genera of Old World monkeys. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow baboon, the Kinda baboon and the chacma ba ...
s. ''P. robustus'' society may have been
patrilocal
In social anthropology, patrilocal residence or patrilocality, also known as virilocal residence or virilocality, are terms referring to the social system in which a married couple resides with or near the husband's parents. The concept of locat ...
, with adult females more likely to leave the group than males, but males may have been more likely to be evicted as indicated by higher male mortality rates and assumed increased risk of predation to solitary individuals. ''P. robustus'' contended with
sabertooth cat
Machairodontinae is an extinct subfamily of carnivoran mammals of the family Felidae (true cats). They were found in Asia, Africa, North America, South America, and Europe from the Miocene to the Pleistocene, living from about 16 million ...
s,
leopard
The leopard (''Panthera pardus'') is one of the five extant species in the genus '' Panthera'', a member of the cat family, Felidae. It occurs in a wide range in sub-Saharan Africa, in some parts of Western and Central Asia, Southern Russia, a ...
s, and
hyena
Hyenas, or hyaenas (from Ancient Greek , ), are feliform carnivoran mammals of the family Hyaenidae . With only four extant species (each in its own genus), it is the fifth-smallest family in the Carnivora and one of the smallest in the clas ...
s on the mixed, open-to-closed landscape, and ''P. robustus'' bones probably accumulated in caves due to big cat predation. It is typically found in what were mixed open and wooded environments, and may have gone extinct in the
Mid-Pleistocene Transition
The Mid-Pleistocene Transition (MPT), also known as the Mid-Pleistocene Revolution (MPR), is a fundamental change in the behaviour of glacial cycles during the Quaternary glaciations. The transition happened approximately 1.25–0.7 milli ...
characterised by the continual prolonging of dry cycles and subsequent retreat of such habitat.
Taxonomy
Research history
Discovery
The first remains, a partial skull including a part of the jawbone ( TM 1517), were discovered in June 1938 at the Kromdraai cave site, South Africa, by local schoolboy Gert Terblanche. He gave the remains to South African conservationist Charles Sydney Barlow, who then relayed them to South African palaeontologist
Robert Broom
Robert Broom FRS FRSE (30 November 1866 6 April 1951) was a British- South African doctor and palaeontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University of Glasgow.
From 1903 to 1910, he ...
. Broom began investigating the site, and, a few weeks later, recovered a right distal
humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
(the lower part of the upper arm bone), a proximal right
ulna
The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
(upper part of a lower arm bone) and a
distal phalanx
The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...
bone of the big toe, all of which he assigned to TM 1517. He also identified a distal toe phalanx which he believed belonged to a
baboon
Baboons are primates comprising the genus ''Papio'', one of the 23 genera of Old World monkeys. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow baboon, the Kinda baboon and the chacma ba ...
, but has since been associated with TM 1517. Broom noted the Kromdraai remains were especially
robust
Robustness is the property of being strong and healthy in constitution. When it is transposed into a system, it refers to the ability of tolerating perturbations that might affect the system’s functional body. In the same line ''robustness'' ca ...
compared to other
hominin
The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos) and in standard usage excludes the genus ''Gorilla'' (gorillas).
The t ...
s. In August 1938, Broom classified the robust Kromdraai remains into a new
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
, as ''Paranthropus robustus''. "''
Paranthropus
''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: ''Paranthropus robustus, P. robustus'' and ''P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be sy ...
''" derives from the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
παρα ''para'', beside or alongside; and άνθρωπος ''ánthropos'', man.
At this point in time, Australian anthropologist
Raymond Dart
Raymond Arthur Dart (4 February 1893 – 22 November 1988) was an Australian anatomist and anthropologist, best known for his involvement in the 1924 discovery of the first fossil ever found of ''Australopithecus africanus'', an extinct homi ...
had made the very first claim (quite controversially at the time) of an early
ape
Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its sister g ...
-like human ancestor in 1924 from South Africa, ''
Australopithecus africanus
''Australopithecus africanus'' is an extinct species of australopithecine which lived between about 3.3 and 2.1 million years ago in the Late Pliocene to Early Pleistocene of South Africa. The species has been recovered from Taung, Sterkfonte ...
'', based on the
Taung child
The Taung Child (or Taung Baby) is the fossilised skull of a young ''Australopithecus africanus''. It was discovered in 1924 by quarrymen working for the Northern Lime Company in Taung, South Africa. Raymond Dart described it as a new species ...
. In 1936, Broom had described "''Plesianthropus transvaalensis''" (now synonymised with ''A. africanus'') from the Sterkfontein Caves only west from Kromdraai. All these species dated to the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
and were found in the same general vicinity (now called the " Cradle of Humankind"). Broom considered them evidence of a greater diversity of hominins in the
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Swartkrans
Swartkrans is a fossil-bearing cave designated as a South African National Heritage Site, located about from Johannesburg. It is located in the Cradle of Humankind World Heritage Site and is notable for being extremely rich in archaeological m ...
Cave in 1948. ''P. robustus'' was only definitively identified at Kromdraai and Swartkrans until around the turn of the century when the species was reported elsewhere in the Cradle of Humankind at Sterkfontein,
Gondolin
In Tolkien's legendarium, Gondolin was a secret city of Elves in the First Age of Middle-earth. The story of the Fall of Gondolin tells of the founding of the city; of the arrival there of Tuor, a prince of Men; of the betrayal of the city to Mor ...
Drimolen
The Drimolen Palaeocave System consists of a series of terminal Pliocene to early Pleistocene hominin-bearing palaeocave fills located around north of Johannesburg, South Africa, and about north of Sterkfontein in the UNESCO World Heritage Site ...
Caves. The species has not been found outside this small area.
"''P. crassidens''"
In 1948, at the nearby Swartkrans Cave, Broom described "''P. crassidens''" (distinct from ''P. robustus'') based on a subadult jaw, SK 6, because Swartkrans and Kromdraai clearly dated to different time intervals based on the diverging animal assemblages in these caves. At this point in time, humans and allies were classified into the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Hominidae, and non-human great apes into "
Pongidae
Pongidae , or the pongids is an obsolete primate taxon containing chimpanzees, gorillas and orangutans. By this definition pongids were also called "great apes". This taxon is not used today but is of historical significance. The great apes ar ...
"; in 1950, Broom suggested separating early hominins into the
subfamilies
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...
Australopithecinae (''Au. africanus'' and "''Pl. transvaalensis''"), "Paranthropinae" (''Pa. robustus'' and "''Pa. crassidens''"), and "Archanthropinae" ("''Au. prometheus''"). This scheme was widely criticised for being too liberal in demarcating species. Further, the remains were not firmly dated, and it was debated if there were indeed multiple hominin lineages or if there was only a single one leading to humans. Most prominently, Broom and South African palaeontologist
John Talbot Robinson
John Talbot Robinson FRSSAf (10 January 1923 – 12 October 2001) was a distinguished South African hominin paleontologist. His most famous discovery (with Robert Broom) was the nearly complete fossil skull of the hominin species '' Australop ...
continued arguing for the validity of ''Paranthropus''.
Anthropologists
Sherwood Washburn
Sherwood Larned Washburn ( – ), nicknamed "Sherry", was an American physical anthropologist, and "a legend in the field." He was pioneer in the field of primatology, opening it to the study of primates in their natural habitats. His research ...
and Bruce D. Patterson were the first to recommend synonymising ''Paranthropus'' with ''
Australopithecus
''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Australopi ...
'' in 1951, wanting to limit hominin genera to only that and ''
Homo
''Homo'' () is the genus that emerged in the (otherwise extinct) genus ''Australopithecus'' that encompasses the extant species ''Homo sapiens'' ( modern humans), plus several extinct species classified as either ancestral to or closely relate ...
'', and it has since been debated whether or not ''Paranthropus'' is a
junior synonym
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
of ''Australopithecus''. In the spirit of tightening
splitting
Splitting may refer to:
* Splitting (psychology)
* Lumpers and splitters, in classification or taxonomy
* Wood splitting
* Tongue splitting
* Splitting, railway operation
Mathematics
* Heegaard splitting
* Splitting field
* Splitting principle
...
criteria for hominin taxa, in 1954, Robinson suggested demoting "''P. crassidens''" to subspecies level as "''P. r. crassidens''", and also moved the Indonesian ''
Meganthropus
''Meganthropus'' is an extinct genus of non-hominin hominid ape, known from the Pleistocene of Indonesia. It is known from a series of large jaw and Hominid skull, skull fragments found at the Sangiran site near Surakarta in Central Java (island) ...
'' into the genus as "''P. palaeojavanicus''". ''Meganthropus'' has since been variously reclassified as a synonym of the Asian ''
Homo erectus
''Homo erectus'' (; meaning "upright man") is an extinct species of archaic human from the Pleistocene, with its earliest occurrence about 2 million years ago. Several human species, such as '' H. heidelbergensis'' and '' H. antecessor' ...
orangutan
Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...
s), and so on, and in 2019 it was again argued to be a valid genus.
In 1949, also in Swartkrans Cave, Broom and Robinson found a mandible which they preliminary described as "intermediate between one of the ape-men and true man," classifying it as a new genus and species "''Telanthropus capensis''". Most immediate reactions favoured synonymising "''T. capensis''" with "''P. crassidens''", whose remains were already abundantly found in the cave. In 1957, though, Italian biologist Alberto Simonetta moved it to the genus "''Pithecanthropus''", and Robinson (without a specific reason why) decided to synonymise it with ''H. erectus'' (African ''H. erectus'' are sometimes called '' H. ergaster'' today). In 1965, South African palaeoanthropologist
Phillip V. Tobias
Phillip Vallentine Tobias (14 October 1925 – 7 June 2012) was a South African palaeoanthropologist and Professor Emeritus at the University of the Witwatersrand in Johannesburg. He was best known for his work at South Africa's hominid fossil ...
questioned whether this classification is completely sound or not.
By the 21st century, "''P. crassidens''" had more or less fallen out of use in favour of ''P. robustus''. American palaeoanthropologist
Frederick E. Grine
Frederick Edward Grine is an American paleoanthropologist. He is a Professor of anthropology and anatomical sciences at the State University of New York at Stony Brook.
He received his bachelor's degree from Washington & Jefferson College, and his ...
is the primary opponent of synonymisation of the two species.
''Gigantopithecus''
In 1939, Broom hypothesised that ''P. robustus'' was closely related to the similarly large-toothed ape ''
Gigantopithecus
''Gigantopithecus'' ( ; ) is an extinct genus of ape from roughly 2 million to 350,000 years ago during the Early Pleistocene, Early to Middle Pleistocene of southern China, represented by one species, ''Gigantopithecus blacki''. Potential identi ...
'' from Asia (extinct apes were primarily known from Asia at the time) believing ''Gigantopithecus'' to have been a hominin. Primarily influenced by the mid-century opinions of Jewish German anthropologist
Franz Weidenreich
Franz Weidenreich (7 June 1873 – 11 July 1948) was a Jewish German anatomist and physical anthropology, physical anthropologist who studied evolution.
Life and career
Weidenreich studied at the Kaiser-Wilhelm-Universität in Strasbourg whe ...
and German-Dutch palaeontologist Ralph von Koenigswald that ''Gigantopithecus'' was, respectively, the direct ancestor of the Asian ''H. erectus'' or closely related, much debate followed over whether ''Gigantopithecus'' was a hominin or a non-human ape.
In 1972, Robinson suggested including ''Gigantopithecus'' in "Paranthropinae", with the
Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
Pakistani "''G. bilaspurensis''" (now ''
Indopithecus
''Indopithecus giganteus'' () is an extinct species of large ape that lived in the late Miocene of the Siwalik Hills in northern India. Although frequently assigned to the more well-known genus '' Gigantopithecus'', recent authors consider it ...
'') as the ancestor of ''Paranthropus'' and the Chinese ''G. blacki''. He also believed that they both had a massive build. In contrast, he reported a very small build for ''A. africanus'' (which he referred to as "''Homo''" ''africanus'') and speculated it had some cultural and hunting abilities, being a member of the human lineage, which "paranthropines" lacked. With the popularisation of
cladistic
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
s by the late 1970s to 1980s, and better resolution on how Miocene apes relate to later apes, ''Gigantopithecus'' was entirely removed from
Homininae
Homininae (), also called "African hominids" or "African apes", is a subfamily of Hominidae. It includes two tribes, with their extant as well as extinct species: 1) the tribe Hominini (with the genus ''Homo'' including modern humans and numerou ...
, and is now placed in the subfamily
Ponginae
Ponginae , also known as the Asian hominids, is a subfamily in the family Hominidae. Once a diverse lineage of Eurasian apes, the subfamily has only one extant genus, '' Pongo'' (orangutans), which contains three extant species; the Sumatran oran ...
with orangutans.
''P. boisei''
In 1959, another and much more robust australopithecine was discovered in East Africa, ''
P. boisei
''Paranthropus boisei'' is a species of australopithecine from the Early Pleistocene of East Africa about 2.5 to 1.15 million years ago. The holotype specimen, OH 5, was discovered by palaeoanthropologist Mary Leakey in 1959, and species descrip ...
'', and in 1975, the ''P. boisei'' skull
KNM-ER 406 KNM ER 406 is an almost complete fossilized skull of the species '' Paranthropus boisei''. It was discovered in Koobi Fora, Kenya by Richard Leakey and H. Mutua in 1969. This species is grouped with the '' Australopitecine'' genus, '' Paranthropus b ...
was demonstrated to have been contemporaneous with the ''H. ergaster/H. erectus'' skull
KNM ER 3733
KNM ER 3733 is a fossilized hominidae, hominid cranium of the extinct hominid ''Homo ergaster'', alternatively referred to as African ''Homo erectus''. It was discovered in 1975 in Koobi Fora, Kenya, right next to Lake Turkana, in a survey led by ...
(which is considered a human ancestor). This is generally taken to show that ''Paranthropus'' was a
sister taxon
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and t ...
to ''Homo'', both developing from some ''Australopithecus'' species, which at the time only included ''A. africanus''.
In 1979, a year after describing '' A. afarensis'' from East Africa, anthropologists
Donald Johanson
Donald Carl Johanson (born June 28, 1943) is an American paleoanthropologist. He is known for discovering, with Yves Coppens and Maurice Taieb, the fossil of a female hominin australopithecine known as "Lucy" in the Afar Triangle region of Hada ...
and
Tim D. White
Tim D. White (born August 24, 1950) is an American paleoanthropologist and Professor of Integrative Biology at the University of California, Berkeley. He is best known for leading the team which discovered Ardi, the type specimen of ''Ardipithe ...
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. Now, the earliest-known South African australopithecine ("
Little Foot
"Little Foot" (Stw 573) is the nickname given to a nearly complete Australopithecus fossil skeleton found in 1994–1998 in the cave system of Sterkfontein, South Africa.
Originally nicknamed "little foot" in 1995 when four ankle bones in a mus ...
") dates to 3.67 million years ago, contemporaneous with ''A. afarensis''. The matter is still debated.
It was long assumed that if ''Paranthropus'' is a valid genus then ''P. robustus'' was the ancestor of ''P. boisei'', but in 1985, anthropologists
Alan Walker
Alan Olav Walker (born 24 August 1997) is a British-born Norwegian music producer and DJ primarily known for the critically acclaimed single " Faded" (2015), which was certified platinum in 14 countries. He has also made several songs including ...
and
Richard Leakey
Richard Erskine Frere Leakey (19 December 1944 – 2 January 2022) was a Kenyan paleoanthropologist, conservationist and politician. Leakey held a number of official positions in Kenya, mostly in institutions of archaeology and wildlife conse ...
found that the 2.5-million-year-old East African skull
KNM WT 17000
KNM-WT 17000 (also known as "The Black Skull") is a fossilized adult skull of the species ''Paranthropus aethiopicus''. It was discovered in West Turkana, Kenya by Alan Walker in 1985. Estimated to be 2.5 million years old, it is an adult with ...
—which they assigned to a new species ''
A. aethiopicus
''Paranthropus aethiopicus'' is an extinct species of robust australopithecine from the Late Pliocene to Early Pleistocene of East Africa about 2.7–2.3 million years ago. However, it is much debated whether or not ''Paranthropus'' is an invali ...
''—was ancestral to ''A. boisei'' (they considered ''Paranthropus'' synonymous with ''Australopithecus''), thus establishing the ''boisei'' lineage as beginning long before ''robustus'' had existed.
Classification
The genus ''Paranthropus'' (otherwise known as "robust australopithecines", in contrast to the " gracile australopithecines") now also includes the East African ''P. boisei'' and ''P. aethiopicus''. It is still debated if this is a valid natural grouping (
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
) or an invalid grouping of similar-looking hominins (
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
). Because skeletal elements are so limited in these species, their affinities with each other and with other
australopithecine
Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally ''Australopithecus'' (cladistically including the genus, genera ''Homo'', ''Paranthropus'', and ''Kenyanthropus''), and it typically in ...
s are difficult to gauge with accuracy. The jaws are the main argument for monophyly, but jaw anatomy is strongly influenced by diet and environment, and could have evolved independently in ''P. robustus'' and ''P. boisei''. 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''. In 2020, palaeoanthropologist Jesse M. Martin and colleagues'
phylogenetic analyses
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
reported the monophyly of ''Paranthropus'', but also that ''P. robustus'' had branched off before ''P. aethiopicus'' (that ''P. aethiopicus'' was ancestral to only ''P. boisei''). The exact classification of ''Australopithecus'' species with each other is quite contentious.
Anatomy
Head
Skull
Typical of ''Paranthropus'', ''P. robustus'' exhibits
post-canine megadontia
Post-canine megadontia is a relative enlargement of the molars and premolars compared to the size of the incisors and canines. This phenomenon is seen in some early hominid ancestors such as ''Paranthropus aethiopicus.''
Archaeological evidence ...
incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...
s and
canines
Canine may refer to:
Zoology and anatomy
* a dog-like Canid animal in the subfamily Caninae
** ''Canis'', a genus including dogs, wolves, coyotes, and jackals
** Dog, the domestic dog
* Canine tooth, in mammalian oral anatomy
People with the surn ...
. The
premolar
The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...
s are shaped like
molars
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
. The enamel thickness on the cheek teeth is relatively on par with that of modern humans, though australopithecine cheek tooth enamel thickens especially at the tips of the cusps, whereas in humans it thickens at the base of the cusps.
''P. robustus'' has a tall face with slight prognathism (the jaw jutted out somewhat). The skulls of males have a well-defined
sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exceptiona ...
on the midline of the skullcap and inflated
cheek
The cheeks ( la, buccae) constitute the area of the face below the eyes and between the nose and the left or right ear. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve. The area between the inside ...
bones, which likely supported massive
temporal muscle
In anatomy, the temporalis muscle, also known as the temporal muscle, is one of the muscles of mastication (chewing). It is a broad, fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomatic a ...
s important in biting. The cheeks project so far from the face that, when in top-view, the nose appears to sit at the bottom of a concavity (a dished face). This displaced the
eye socket
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is , of ...
s forward somewhat, causing a weak brow ridge and receding forehead. The inflated cheeks also would have pushed the
masseter muscle
In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it ...
(important in biting down) forward and pushed the tooth rows back, which would have created a higher
bite force
Bite force quotient (BFQ) is a numerical value commonly used to represent the bite force of an animal, while also taking factors like the animal's size into account.
The BFQ is calculated as the regression of the quotient
In arithmetic, a ...
on the premolars. The ramus of the jawbone, which connects the lower jaw to the upper jaw, is tall, which would have increased
lever arm
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of ...
(and thereby, torque) of the masseter and medial pterygoid muscles (both important in biting down), further increasing bite force.
The well-defined sagittal crest and inflated cheeks are absent in the presumed-female skull DNH-7, so Keyser suggested that male ''P. robustus'' may have been more heavily built than females (''P. robustus'' was
sexually dimorphic
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
). The Drimolen material, being more basal, is comparatively more gracile and consequently probably had a smaller bite force than the younger Swartkrans and Kromdraii ''P. robustus''. The brows of the former also are rounded off rather than squared, and the sagittal crest of the presumed-male DNH 155 is more posteriorly (towards the back of the head) positioned.
The posterior semicircular canals in the
inner ear
The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...
of
SK 46
SK 46 is the fossilized partial cranium and palate of the species ''Paranthropus robustus''. It was discovered in Swartkrans, South Africa by local quarrymen and Robert Broom in 1949.
It is estimated to be 1.5-1.8 million years old.
Its characte ...
and SK 47 are unlike those of the apelike ''Australopithecus'' or ''Homo'', suggesting different locomotory and head movement patterns, since inner ear anatomy affects the
vestibular system
The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...
(sense of balance). The posterior semicircular canals of modern humans are thought to aid in stabilisation while running, which could mean ''P. robustus'' was not an endurance runner.
Brain
Upon describing the species, Broom estimated the fragmentary braincase of TM 1517 as 600 cc, and he, along with South African anthropologist Gerrit Willem Hendrik Schepers, revised this to 575–680 cc in 1946. For comparison, the brain volume of contemporary ''Homo'' varied from 500 to 900 cc. A year later, British primatologist
Wilfrid Le Gros Clark
Sir Wilfrid Edward Le Gros Clark (5 June 1895 – 28 June 1971) was a British anatomist, surgeon, primatologist and palaeoanthropologist, today best remembered for his contribution to the study of human evolution. He was Dr Lee's Professor of ...
commented that, since only a part of the
temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex.
The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. Th ...
on one side is known, brain volume cannot be accurately measured for this specimen. In 2001, Polish anthropologist Katarzyna Kaszycka said that Broom quite often artificially inflated brain size in early hominins, and the true value was probably much lower.
In 1972, American physical anthropologist
Ralph Holloway Ralph Leslie Holloway, Jr. (born 1935) is a physical anthropologist at Columbia University and research associate with the American Museum of Natural History. Since obtaining his Ph.D from the University of California, Berkeley in 1964, Holloway ha ...
measured the skullcap SK 1585, which is missing part of the
frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, par ...
, and reported a volume of about 530 cc. He also noted that, compared to other australopithecines, ''Paranthropus'' seems to have had an expanded
cerebellum
The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...
like ''Homo'', echoing what Tobias said while studying ''P. boisei'' skulls in 1967. In 2000, American neuroanthropologist
Dean Falk
Dean Falk (born June 25, 1944) is an American academic neuroanthropologist who specializes in the evolution of the brain and cognition in higher primates. She is the Hale G. Smith Professor of Anthropology and a Distinguished Research Professor ...
and colleagues filled in frontal bone anatomy of SK 1585 using the ''P. boisei'' specimens KNM-ER 407,
OH 5
''Paranthropus boisei'' is a species of australopithecine from the Early Pleistocene of East Africa about 2.5 to 1.15 million years ago. The holotype specimen, OH 5, was discovered by palaeoanthropologist Mary Leakey in 1959, and described by h ...
, and KNM-ER 732, and recalculated the brain volume to about 476 cc. They stated overall brain anatomy of ''P. robustus'' was more like that of non-human apes.
In 2020, the nearly complete skull DNH 155 was discovered and was measured to have had a brain volume of 450 cc.
Blood vessels
In 1983, while studying SK 1585 (''P. robustus'') and KNM-ER 407 (''P. boisei'', which he referred to as ''robustus''), French anthropologist Roger Saban stated that the parietal branch of the
middle meningeal artery
The middle meningeal artery ('' la, arteria meningea media'') is typically the third branch of the first portion of the maxillary artery. After branching off the maxillary artery in the infratemporal fossa, it runs through the foramen spinosum to ...
originated from the posterior branch in ''P. robustus'' and ''P. boisei'' instead of the anterior branch as in earlier hominins, and considered this a derived characteristic due to increased brain capacity. It has since been demonstrated that, at least for ''P. boisei'', the parietal branch could originate from either the anterior or posterior branches, sometimes both in a single specimen on opposite sides of the skull.
Regarding the
dural venous sinuses
The dural venous sinuses (also called dural sinuses, cerebral sinuses, or cranial sinuses) are venous channels found between the endosteal and meningeal layers of dura mater in the brain. They receive blood from the cerebral veins, receive cereb ...
, in 1983, Falk and anthropologist Glenn Conroy suggested that, unlike ''A. africanus'' or modern humans, all ''Paranthropus'' (and ''A. afarensis'') had expanded
occipital
The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...
and marginal (around the
foramen magnum
The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
) sinuses, completely supplanting the
transverse
Transverse may refer to:
*Transverse engine, an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle
*Transverse flute, a flute that is held horizontally
* Transverse force (or ''Euler force''), the tangen ...
and
sigmoid sinus
The sigmoid sinuses (sigma- or s-shaped hollow curve), also known as the , are venous sinuses within the skull that receive blood from posterior dural venous sinus veins.
Structure
The sigmoid sinus is a dural venous sinus situated within the du ...
es. They suggested the setup would have increased blood flow to the
internal vertebral venous plexuses
The internal vertebral venous plexuses (intraspinal veins) lie within the vertebral canal in the epidural space, and receive tributaries from the bones and from the spinal cord.
They form a closer network than the external plexuses, and, running m ...
or
internal jugular vein
The internal jugular vein is a paired jugular vein that collects blood from the brain and the superficial parts of the face and neck. This vein runs in the carotid sheath with the common carotid artery and vagus nerve.
It begins in the posteri ...
, and was thus related to the reorganisation of the blood vessels supplying the head as an immediate response to
biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' a ...
alism, which relaxed as bipedalism became more developed. In 1988, Falk and Tobias demonstrated that early hominins (at least ''A. africanus'' and ''P. boisei'') could have both an occipital/marginal and transverse/sigmoid systems concurrently or on opposite halves of the skull.
Torso
Few
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e are assigned to ''P. robustus''. The only thoracolumbar series (
thoracic
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
and
lumbar
In tetrapod anatomy, lumbar is an adjective that means ''of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum.''
The lumbar region is sometimes referred to as the lower spine, or as an area of the back i ...
series) preserved belongs to the juvenile SKW 14002, and either represents the 1st to the 4th lumbar vertebrae, or the 2nd to the 5th. SK 3981 preserves a 12th thoracic vertebra (the last in the series), and a lower lumbar vertebra. The 12th thoracic vertebra is relatively elongated, and the articular surface (where it joins with another vertebra) is
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...
-shaped. The T12 is more compressed in height than that of other australopithecines and modern apes. Modern humans which suffer from
spinal disc herniation
Spinal disc herniation is an injury to the cushioning and connective tissue between vertebrae, usually caused by excessive strain or trauma to the spine. It may result in back pain, pain or sensation in different parts of the body, and physical ...
often have vertebrae that are more similar to those of
chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s than healthy humans. Early hominin vertebrae are similar to those of a pathological human, including the only other 12th thoracic vertebra known for ''P. robustus'', the juvenile SK 853. Conversely, SK 3981 is more similar to those of healthy humans, which could be explained as: SK 3981 is abnormal, the vertebrae took on a more humanlike condition with maturity, or one of these specimens is assigned to the wrong species. The shape of the lumbar vertebrae is much more similar to that of
Turkana Boy
Turkana Boy, also called Nariokotome Boy, is the name given to fossil KNM-WT 15000, a nearly complete skeleton of a ''Homo ergaster'' youth who lived 1.5 to 1.6 million years ago. This specimen is the most complete early hominin skeleton ever ...
(''H. ergaster''/''H. erectus'') and humans than other australopithecines. The pedicles (which jut out diagonally from the vertebra) of the lower lumbar vertebra are much more robust than in other australopithecines and are within the range of humans, and the transverse processes (which jut out to the sides of the vertebra) indicate powerful
iliolumbar ligament
The iliolumbar ligament is a strong ligament passing from the tip of the transverse process of the fifth lumbar vertebra to the posterior part of the inner lip of the iliac crest (upper margin of ilium).
Course
It forms the thickened lower bord ...
s. These could have bearing on the amount of time spent upright compared to other australopithecines.
The
pelvis
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ...
is similar to the pelvises of ''A. africanus'' and ''A. afarensis'', but it has a wider
iliac blade
The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis.
Structure
The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the posteri ...
and smaller
acetabulum
The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.
Structure
There are three bones of the ''os coxae'' (hip bone) that c ...
and hip joint. Like modern humans, the ilium of ''P. robustus'' features development of the surface and thickening of the
posterior superior iliac spine
The posterior border of the ala, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. The posterior superior iliac spine serves for the attachment ...
, which are important in stabilising the
sacrum
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ...
, and indicates
lumbar lordosis
Lordosis is historically defined as an ''abnormal'' inward curvature of the lumbar spine. However, the terms ''lordosis'' and ''lordotic'' are also used to refer to the normal inward curvature of the lumbar and cervical regions of the human spin ...
(curvature of the lumbar vertebrae) and thus bipedalism. The anatomy of the sacrum and the first lumbar vertebra (at least the vertebral arch), preserved in DNH 43, are similar to those of other australopithecines. The pelvis seems to indicate a more-or-less humanlike hip joint consistent with bipedalism, though differences in overall pelvic anatomy may indicate ''P. robustus'' used different muscles to generate force and perhaps had a different mechanism to direct force up the spine. This is similar to the condition seen in ''A. africanus''. This could potentially indicate the lower limbs had a wider range of motion than those of modern humans.
Limbs
The distal (lower)
humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
of ''P. robustus'' falls within the variation of both modern humans and chimps, as the distal humerus is quite similar between humans and chimpanzees. The
radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
of ''P. robustus'' is comparable in form to ''Australopithecus'' species. The
wrist
In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...
joint had the same maneuverability as that of modern humans rather than the greater
flexion
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
achieved by non-human apes, but the
head of radius
The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the ra ...
(the
elbow
The elbow is the region between the arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and the media ...
) seems to have been quite capable of maintaining stability when the forearm was flexed like non-human apes. It is possible this reflects some
arboreal
Arboreal locomotion is the Animal locomotion, locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. Th ...
activity (movement in the trees) as is controversially postulated in other australopithecines. SKX 3602 exhibits robust
radial styloid process
The radial styloid process is a projection of bone on the lateral surface of the distal radius bone.
Structure
The radial styloid process is found on the lateral surface of the distal radius bone. It extends obliquely downward into a strong, c ...
es near the hand which indicate strong
brachioradialis muscle
The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm. It is attached to the distal styloid process of the radius by way o ...
s and extensor retinaculae. Like humans, the finger bones are uncurved and have weaker muscle attachment than non-human apes, though the
proximal phalanges
The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones.
...
are smaller than in humans. The intermediate phalanges are stout and straight like humans, but have stouter bases and better developed flexor impressions. The distal phalanges seem to be essentially humanlike. These could indicate a decreased climbing capacity compared to non-human apes and ''P. boisei''. The ''P. robustus'' hand is consistent with a humanlike
precision grip
A tactile pad is an area of skin that is particularly sensitive to pressure, temperature, or pain. Tactile pads are characterized by high concentrations of free nerve endings. In primates, the last Hand, phalanges in the fingers and toes have tact ...
which would have made possible the production or usage of tools requiring greater motor functions than non-human primate tools.
The femur, as in ''P. boisei'' and ''H. habilis'', is flattened anteroposteriorly (on the front and back side). This may indicate a walking gait more similar to early hominins than to modern humans (less efficient gait). Four femora assigned to ''P. robustus''—SK 19, SK 82, SK 97, and SK 3121—exhibit an apparently high
anisotropic
Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...
trabecular bone
A trabecula (plural trabeculae, from Latin for "small beam") is a small, often microscopic, tissue element in the form of a small beam, strut or rod that supports or anchors a framework of parts within a body or organ. A trabecula generally has ...
(at the hip joint) structure, which could indicate reduced mobility of the hip joint compared to non-human apes, and the ability to produce forces consistent with humanlike bipedalism. The
femoral head
The femoral head (femur head or head of the femur) is the highest part of the thigh bone (femur). It is supported by the femoral neck.
Structure
The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a l ...
StW 311, which either belongs to ''P. robustus'' or early ''Homo'', seems to have habitually been placed in highly flexed positions based on the wearing patterns, which would be consistent with frequent climbing activity. It is unclear if frequent squatting could be a valid alternative interpretation. The textural complexity of the
kneecap
The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as m ...
SKX 1084, which reflects
cartilage
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...
thickness and thus usage of the knee joint and bipedality, is midway between modern humans and chimps. The big toe bone of ''P. robustus'' is not dextrous, which indicates a humanlike foot posture and range of motion, but the more distal ankle joint would have inhibited the modern human toe-off gait cycle. ''P. robustus'' and ''H. habilis'' may have achieved about the same grade of bipedality.
Size
Broom had noted that the ankle bone and humerus of the holotype TM 1517 were about the same dimensions as that of a modern San woman, and so assumed humanlike proportions in ''P. robustus''. In 1972, Robinson estimated ''Paranthropus'' as having been massive. He calculated the humerus-to-femur ratio of ''P. robustus'' by using the presumed female humerus of STS 7 and comparing it with the presumed male femur of STS 14. He also had to estimate the length of the humerus using the femur assuming a similar degree of sexual dimorphism between ''P. robustus'' and humans. Comparing the ratio to humans, he concluded that ''P. robustus'' was a heavily built species with a height of and a weight of . Consequently, Robinson had described its locomotory habits as, "a compromise between erectness and facility for quadrupedal climbing." In contrast, he estimated ''A. africanus'' (which he called "''H.''" ''africanus'') to have been tall and in weight, and to have also been completely bipedal.
This was soon challenged in 1974 by American palaeontologist
Stephen Jay Gould
Stephen Jay Gould (; September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was one of the most influential and widely read authors of popular science of his generation. Gould sp ...
and English palaeoanthropologist
David Pilbeam
David Pilbeam (born 21 November 1940 in Brighton, Sussex, England) is the Henry Ford II Professor of the Social Sciences at Harvard University and curator of paleoanthropology at the Peabody Museum of Archaeology and Ethnology. He is a member of ...
, who guessed from the available skeletal elements a much lighter weight of about . Similarly, in 1988, American anthropologist
Henry McHenry
Henry Malcolm McHenry (born May 19, 1944) is a professor of anthropology at the University of California, Davis, specializing in studies of human evolution, the origins of bipedality, and paleoanthropology.
McHenry has published on the comparativ ...
reported much lighter weights as well as notable sexual dimorphism for ''Paranthropus''. McHenry plotted body size vs. the cross sectional area of the femoral head for a sample of just humans and a sample with all great apes including humans, and calculated
linear regression
In statistics, linear regression is a linear approach for modelling the relationship between a scalar response and one or more explanatory variables (also known as dependent and independent variables). The case of one explanatory variable is call ...
s for each one. Based on the average of these two regressions, he reported an average weight of for ''P. robustus'' using the specimens SK 82 and SK 97. In 1991, McHenry expanded his sample size, and also estimated the living size of Swartkrans specimens by scaling down the dimensions of an average modern human to meet a preserved leg or foot element (he considered the arm measurements too variable among hominins to give accurate estimates). At Members 1 and 2, about 35% of the ''P. robustus'' leg or foot specimens were the same size as those in a human, 22% in a human, and the remaining 43% bigger than the former but less than a human except for KNM‐ER 1464 (an
ankle bone
The talus (; Latin for ankle or ankle bone), talus bone, astragalus (), or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body from the ...
). At Member 3, all individuals were consistent with a human. Smaller adults thus seem to have been more common. McHenry also estimated the living height of 3 ''P. robustus'' specimens (male SK 82, male SK 97, and female or subadult SK 3155), by scaling down an average human to meet the estimated size of the preserved femur, as , , and , respectively. Based on just these three, he reported an average height of for ''P. robustus'' males and for females.
In 2001, palaeoanthropologist Randall L. Susman and colleagues, using two recently discovered proximal femoral fragments from Swartkrans, estimated an average of for males and for females. If these four proximal femur specimens—SK 82, SK 97, SKW 19, and SK 3121—are representative of the entire species, they said that this degree of sexual dimorphism is greater than what is exhibited in
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
s and
chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s, but less than
orangutan
Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...
s and
gorilla
Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s. Female ''P. robustus'' were about the same estimated weight as female ''H. ergaster/H. erectus'' in Swartkrans, but they estimated male ''H. ergaster/H. erectus'' as much bigger at . In 2012, American anthropologist Trenton Holliday, using the same equation as McHenry on 3 specimens, reported an average of with a range of . In 2015, biological anthropologist Mark Grabowski and colleagues, using 9 specimens, estimated an average of for males and for females.
Palaeobiology
Diet
In 1954, Robinson suggested that the heavily built skull of ''P. robustus'' and resultantly exorbitant bite force was indicative of a specialist diet adapted for frequently cracking hard foods such as nuts. Because of this, the predominant model of ''Paranthropus'' extinction for the latter half of the 20th century was that they were unable to adapt to the volatile climate of the Pleistocene, unlike the much more adaptable ''Homo''. Subsequent researchers reinforced this model studying the musculature of the face, dental wearing patterns, and primate ecology. In 1981, English anthropologist Alan Walker, while studying the ''P. boisei'' skulls KNM-ER 406 and 729, pointed out that bite force is a measure of not only the total pressure exerted but also the surface area of the tooth over which the pressure is being exerted, and ''Paranthropus'' teeth are 4–5 times the size of modern human teeth. Because the chewing muscles are arranged the same way, Walker postulated that the heavy build was instead an adaptation to chew a large quantity of food at the same time. He also found that microwearing on 20 ''P. boisei'' molar specimens were indistinguishable from patterning recorded in
mandrill
The mandrill (''Mandrillus sphinx'') is a large Old World monkey native to west central Africa. It is one of the most colorful mammals in the world, with red and blue skin on its face and posterior. The species is sexually dimorphic, as males ...
s, chimps, and orangutans. Despite subsequent arguments that ''Paranthropus'' were not specialist feeders, the predominant consensus in favour of Robinson's initial model did not change for the remainder of the 20th century.
In 2004, in their review of ''Paranthropus'' dietary literature, anthropologists Bernard Wood and David Strait concluded that ''Paranthropus'' were most definitely generalist feeders, and that ''P. robustus'' was an
omnivore
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...
. They found that the microwear patterns in ''P. robustus'' suggest hard food was infrequently consumed, and therefore the heavy build of the skull was only relevant when eating less desirable fallback foods. 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 chimpanzees (and presumably gracile australopithecines) which require steady access to high quality foods. In 1980, anthropologists Tom Hatley and John Kappelman suggested that early hominins ( convergently with
bear
Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Nor ...
s and
pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...
s) adapted to eating abrasive and calorie-rich underground
storage organ
A storage organ is a part of a plant specifically modified for storage of energy
(generally in the form of carbohydrates) or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have ...
s (USOs), such as roots and tubers. Since then, hominin exploitation of USOs has gained more support. In 2005, biological anthropologists
Greg Laden
Gregory Thomas Laden is an American biological anthropologist and science blogger.
Education
Born in 1958, Laden received his B.A. from the University of the State of New York's Regents College program in 1984, and his M.A. and Ph.D. from Harvard ...
and
Richard Wrangham
Richard Walter Wrangham (born 1948) is an English anthropologist and primatologist; he is Professor of Biological Anthropology at Harvard University. His research and writing have involved ape behavior, human evolution, violence, and cooking.
...
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.
A 2006 carbon isotope analysis suggested that ''P. robustus'' subsisted on mainly C4 savanna plants or C3 forest plants depending on the season, which could indicate either seasonal shifts in diet or seasonal migration from forest to savanna. ''H. ergaster/H. erectus'' appears to have consumed about the same proportion of C3 to C4 based foods as ''P. robustus''. ''P. robustus'' likely also commonly cracked hard foods such as seeds or nuts, as it had a moderate tooth-chipping rate (about 12% in a sample of 239 individuals, as opposed to little to none for ''P. boisei''). A high cavity rate could indicate
honey
Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...
consumption. Juvenile ''P. robustus'' may have relied more on tubers than adults, given the elevated levels of
strontium
Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...
compared to adults in teeth from Swartkrans Cave, which, in the area, was most likely sourced from tubers.
Dentin
Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by ena ...
exposure on juvenile teeth could indicate early weaning, or a more abrasive diet than adults which wore away the
cementum
Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament.Illustrated Dental Embryology, Histology, a ...
and enamel coatings, or both. It is also possible juveniles were instead less capable of removing grit from dug-up food rather than purposefully seeking out more abrasive foods.
Social structure
Given the marked anatomical and physical differences with modern great apes, there may be no modern analogue for australopithecine societies, so comparisons drawn with modern primates are highly speculative.
In 2007, anthropologist Charles Lockwood and colleagues pointed out that ''P. robustus'' appears to have had pronounced
sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
, with males notably larger than females. This is commonly correlated with a male-dominated
polygamous
Crimes
Polygamy (from Late Greek (') "state of marriage to many spouses") is the practice of marriage, marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this polygyny. When a woman is ...
society, such as the harem society of modern forest-dwelling
silverback gorilla
Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s where one male has exclusive breeding rights to a group of females. Estimated male-female size disparity in ''P. robustus'' is comparable to gorillas (based on facial dimensions), and younger males were less robust than older males (delayed maturity is also exhibited in gorillas). Because the majority of sexed ''P. robustus'' specimens are male (or at least presumed male), males seem to have had a higher mortality rate than females. In a harem society, males are more likely to be evicted from the group given higher male–male competition over females, and lone males may have been put at a higher risk of predation. By this hypothesis, a female moving out of her birth group may have spent little time alone and transferred immediately to another established group.
However, in 2011, palaeoanthropologist Sandi Copeland and colleagues studied the strontium isotope ratio of ''P. robustus'' teeth from the
dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
Sterkfontein Valley, and found that like other hominins, but unlike other great apes, ''P. robustus'' females were more likely to leave their place of birth (
patrilocal
In social anthropology, patrilocal residence or patrilocality, also known as virilocal residence or virilocality, are terms referring to the social system in which a married couple resides with or near the husband's parents. The concept of locat ...
). This discounts the plausibility of a harem society, which would have resulted in a
matrilocal
In social anthropology, matrilocal residence or matrilocality (also uxorilocal residence or uxorilocality) is the societal system in which a married couple resides with or near the wife's parents. Thus, the female offspring of a mother remain l ...
society due to heightened male–male competition. Males did not seem to have ventured very far from the valley, which could either indicate small home ranges, or that they preferred dolomitic landscapes due to perhaps cave abundance or factors related to vegetation growth. Similarly, in 2016, Polish anthropologist Katarzyna Kaszycka rebutted that, among primates, delayed maturity is also exhibited in the
rhesus monkey
The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies that are split between two groups, the Chinese-derived and the Indian-derived. Generally b ...
which has a multi-male society, and may not be an accurate indicator of social structure. If ''P. robustus'' preferred a savanna habitat, a multi-male society would have been more conducive in defending the troop from predators in the more exposed environment, much like baboons which live in the savanna. Even in a multi-male society, it is still possible that males were more likely to be evicted, explaining male-skewed mortality with the same mechanism.
In 2017, anthropologist Katharine Balolia and colleagues postulated that, because male non-human great apes have a larger sagittal crest than females (particularly gorillas and orangutans), the crest may be influenced by
sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
in addition to supporting chewing muscles. Further, the size of the sagittal crest (and the
gluteus muscle
The gluteal muscles, often called glutes are a group of three muscles which make up the gluteal region commonly known as the buttocks: the gluteus maximus, gluteus medius and gluteus minimus. The three muscles originate from the ilium and sa ...
s) in male
western lowland gorilla
The western lowland gorilla (''Gorilla gorilla gorilla'') is one of two Critically Endangered subspecies of the western gorilla (''Gorilla gorilla'') that lives in Montane ecosystems#Montane forests, montane, Old-growth forest, primary and sec ...
s has been correlated with reproductive success. Balolia ''et al.'' 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
Display may refer to:
Technology
* Display device, output device for presenting information, including:
** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep
** Electronic visual display, output devi ...
. This contrasts with other primates which flash the typically enlarged canines in agonistic display (''Paranthropus'' likely did not do this as the canines are comparatively small), though it is also possible that the crest is only so prominent in male gorillas and orangutans because they require larger temporalis muscles to achieve a wider gape to better display the canines.
Technology
Cave sites in the Cradle of Humankind often have stone and bone tools, with the former attributed to early ''Homo'' and the latter generally to ''P. robustus'', as bone tools are most abundant when ''P. robustus'' remains far outnumber ''Homo'' remains. Australopithecine bone technology was first proposed by Dart in the 1950s with what he termed the "
osteodontokeratic culture
The Osteodontokeratic ("bone-tooth-horn", Greek and Latin derivation) culture (ODK) is a hypothesis that was developed by Prof. Raymond Dart (who identified the Taung child fossil in 1924, and published the find in ''Nature'' Magazine in 1925), whi ...
", which he attributed to ''A. africanus'' at
Makapansgat
Makapansgat () (or Makapan Valley World Heritage Site) is an archaeological location within the Makapansgat and Zwartkrans Valleys, northeast of Mokopane in Limpopo province, South Africa. It is an important palaeontological site, with the local ...
dating to 3–2.6 million years ago. These bones are no longer considered to have been tools, and the existence of this culture is not supported. The first probable bone tool was reported by Robinson in 1959 at Sterkfontein Member 5. Excavations led by South African palaeontologist
Charles Kimberlin Brain
Charles Kimberlin Brain, also known as C. K. "Bob" Brain (born 7 May 1931, in Southern Rhodesia, now modern Harare, Zimbabwe), is a South African paleontologist who has studied and taught African cave taphonomy for more than fifty years.
Biogr ...
at Swartkrans in the late 1980s and early 1990s recovered 84 similar bone tools, and excavations led by Keyser at Drimolen recovered 23. These tools were all found alongside
Acheulean
Acheulean (; also Acheulian and Mode II), from the French ''acheuléen'' after the type site of Saint-Acheul, is an archaeological industry of stone tool manufacture characterized by the distinctive oval and pear-shaped "hand axes" associated ...
stone tool
A stone tool is, in the most general sense, any tool made either partially or entirely out of stone. Although stone tool-dependent societies and cultures still exist today, most stone tools are associated with prehistoric (particularly Stone Ag ...
s, except for those from Swartkrans Member 1 which bore
Oldowan
The Oldowan (or Mode I) was a widespread stone tool archaeological industry (style) in prehistory. These early tools were simple, usually made with one or a few flakes chipped off with another stone. Oldowan tools were used during the Lower ...
stone tools. Thus, there are 108 bone tool specimens from the region in total, and possibly an additional two from Kromdraai B. The two stone tools (either "Developed Oldowan" or "Early Acheulean") from Kromdraai B could possibly be attributed to ''P. robustus'', as ''Homo'' has not been confidently identified in this layer, though it is possible that the stone tools were reworked (moved into the layer after the inhabitants had died). Bone tools may have been used to cut or process vegetation, process fruits (namely
marula fruit
''Sclerocarya birrea'' ( grc, σκληρός , "hard", and , "nut", in reference to the stone inside the fleshy fruit), commonly known as the marula, is a medium-sized deciduous fruit, fruit-bearing tree, indigenous to the miombo woodlands o ...
), strip tree bark, or dig up tubers or termites. The form of ''P. robustus'' incisors appears to be intermediate between ''H. erectus'' and modern humans, which could possibly mean it did not have to regularly bite off mouthfuls of a large food item due to preparation with simple tools. The bone tools were typically sourced from the shaft of
long bone
The long bones are those that are longer than they are wide. They are one of five types of bones: long, Short bone, short, Flat bone, flat, Irregular bone, irregular and Sesamoid bone, sesamoid. Long bones, especially the femur and tibia, are subj ...
s from medium- to large-sized mammals, but tools sourced from
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
s, ribs, and horn cores have also been found. They were not manufactured or purposefully shaped for a task, but since they display no weathering, and there is a preference displayed for certain bones, raw materials were likely specifically hand picked. This contrasts with East African bone tools which appear to have been modified and directly cut into specific shapes before using.
In 1988, Brain and South African archaeologist A. Sillent analysed the 59,488 bone fragments from Swartkrans Member 3, and found that 270 had been burnt, mainly belonging to medium-sized antelope, but also zebra, warthog, baboon, and ''P. robustus''. They were found across the entire depth of Member 3, so fire was a regular event throughout its deposition. Based on colour and structural changes, they found that 46 were heated to below , 52 to , 45 to , and 127 above this. They concluded that these bones were, "the earliest direct evidence of fire use in the fossil record," and compared the temperatures with those achieved by experimental campfires burning white stinkwood which commonly grows near the cave. Though some bones had cut marks consistent with butchery, they said it was also possible hominins were making fire to scare away predators or for warmth instead of cooking. Because both ''P. robustus'' and ''H. ergaster''/''H. erectus'' were found in the cave, they were unsure which species to attribute the fire to. As an alternative to hominin activity, because the bones were not burnt inside the cave, it is possible that they were naturally burnt in cyclically occurring
wildfire
A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire ...
s (dry savanna grass as well as possible
guano
Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...
or plant accumulation in the cave may have left it susceptible to such a scenario), and then washed into what would become Member 3. The now-earliest claim of fire usage is 1.7 million years ago at
Wonderwerk Cave
Wonderwerk Cave is an archaeological site, formed originally as an ancient solution cavity in dolomite rocks of the Kuruman Hills, situated between Danielskuil and Kuruman in the Northern Cape Province, South Africa. It is a National Heritage S ...
, South Africa, made by South African archaeologist Peter Beaumont in 2011, which he attributed to ''H. ergaster''/''H. erectus''.
Development
Australopithecines are generally considered to have had a faster, apelike growth rate than modern humans largely due to dental development trends. Broadly speaking, the emergence of the first permanent molar in early hominins has been variously estimated anywhere from 2.5 to 4.5 years, which all contrast markedly with the modern human average of 5.8 years. The 1st permanent molar of SK 63, which may have died at 3.4–3.7 years of age, possibly erupted at 2.9–3.2 years. 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 but a slower life history due to environmental factors, such as early weaning age as is exemplified in modern indriid
lemur
Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are Strepsirrhini, wet-nosed primates of the Superfamily (biology), superfamily Lemuroidea (), divided into 8 Family (biology), families and consisting of 15 genera and around 100 exist ...
s. In TM 1517, fusion of the elements of the distal humerus (at the elbow joint) occurred before the fusion of the elements in the distal big toe phalanx, much like in chimps and
bonobo
The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee and less often the dwarf chimpanzee or gracile chimpanzee, is an endangered great ape and one of the two species making up the genus '' Pan,'' the other being the comm ...
s, but unlike humans, which could also indicate an apelike growth trajectory.
While growing, the front part of the jaw in ''P. robustus'' is depository (so it grows) whereas the sides are resorptive (so they recede). For comparison, chimp jaws are generally depository reflecting prognathism, and modern humans resorptive reflecting a flat face. In ''Paranthropus'', this may have functioned to thicken the
palate
The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.
A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...
. Unlike other apes and gracile australopithecines, but like humans, the
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
(on the palate) formed early in development. At early stages, the ''P. robustus'' jawbone was somewhat similar to that of modern humans, but the breadth grew in ''P. robustus'', as to be expected from its incredible robustness in adulthood. By the time the first permanent molar erupts, the
body of the mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
and the front jaw broadened, and the
ramus of the mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
elongated, diverging from the modern human trajectory. Because the ramus was so tall, it is suggested that ''P. robustus'' experienced more anterior face rotation than modern humans and apes. Growth was most marked between the eruptions of the first and second permanent molars, most notably in terms of the distance from the back of the mouth to the front of the mouth, probably to make room for the massive postcanine teeth. Like humans, jaw robustness decreased with age, though it decreased slower in ''P. robustus''. Regardless if ''P. robustus'' followed a human or non-human ape dental development timeframe, the premolars and molars would have had an accelerated growth rate to achieve their massive size. In contrast, the presence of
perikyma
Perikymata (Greek plural of περικύμα, perikyma) are incremental growth lines that appear on the surface of tooth enamel as a series of linear grooves. In anatomically modern humans, each perikyma takes approximately 6–12 days to form. T ...
ta on the incisors and canines (growth lines which typically are worn away after eruption) could indicate these teeth had a reduced growth rate. The tooth roots of ''P. robustus'' molars may have grown at a faster rate than gracile australopithecines; the root length of SK 62's 1st molar, which was reaching emergence from the
dental alveolus
Dental alveoli (singular ''alveolus'') are sockets in the jaws in which the roots of teeth are held in the alveolar process with the periodontal ligament. The lay term for dental alveoli is tooth sockets. A joint that connects the roots of the t ...
, is about . In contrast, those of other hominins reach after the tooth has emerged not only from the gums (a later stage of dental development). SK 62's growth trajectory is more similar to that of gorillas, whose roots typically measure when emerging from the gums.
Females may have reached skeletal maturity by the time the third molar erupted, but males appear to have continued growing after reaching dental maturity, during which time they become markedly more robust than females (
sexual bimaturism
Sexual bimaturism describes a difference in developmental timing between males and females of the same species. Sexual bimaturism can result in sexual dimorphism, but sexual dimorphism could also develop through differential rates of development. I ...
). Similarly, male gorillas complete dental development about the same time as females, but continue growing for up to 5 or 6 years; and male mandrills complete dental development before females, but continue growing for several years more. It is debated whether or not ''P. robustus'' had a defined growth spurt in terms of overall height during adolescence, an event unique to humans among modern apes.
Life history
In 1968, American anthropologist Alan Mann, using dental maturity, stratified ''P. robustus'' specimens from Swartkrans into different ages, and found an average of 17.2 years at death (they did not necessarily die from old age), and the oldest specimen was 30–35 years old. He also reported an average of 22.2 years for ''A. africanus''. Using these, he argued these hominins had a humanlike prolonged childhood. In response, in 1971, biologist Kelton McKinley repeated Mann's process with more specimens, and (including ''P. boisei'') reported an average of 18 years. McKinley agreed with Mann that ''P. robustus'' may have had a prolonged childhood. McKinley also speculated that
sexual maturity
Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definitio ...
was reached at approximately 11 years because it is about halfway between the averages for chimps (9 years) and humans (13). Based on this, he concluded babies were birthed at intervals of 3 to 4 years using a statistical test to maximise the number of children born.
In 1972, after estimating a foetal size of based on an adult female weight of , anthropologist Walter Leutenegger estimated foetal head size at about , similar to a chimp. In 1973, using this and an equation between foetal head size and gestation (assuming foetal growth rate of 0.6 for all mammals), biologist John Frazer estimated a gestation of 300 days for ''P. robustus''. In response, Leutenegger pointed out that apes have highly variable foetal growth rates, and "estimates on gestation periods based on this rate and birth weight are useless."
In 1985, British biologists
Paul H. Harvey
Paul H. Harvey One or more of the preceding sentences incorporates text from the royalsociety.org website where: (born 19 January 1947) is a British evolutionary biologist. He is Professor of Zoology and was head of the zoology department ...
tertiary dentin Tertiary dentin (including reparative dentin or sclerotic dentin) forms as a reaction to stimulation, including caries, wear and fractures. Tertiary dentin is therefore a mechanism for a tooth to ‘heal’, with new material formation protecting th ...
, which forms to repair tooth damage caused by excessive wearing or dental cavities. This is similar to what was found for ''A. africanus'' and ''
H. naledi
'' Homo naledi'' is an extinct species of archaic human discovered in 2013 in the Rising Star Cave, Cradle of Humankind, South Africa dating to the Middle Pleistocene 335,000–236,000 years ago. The initial discovery comprises 1,550 specimens ...
'' (all three inhabited the Cradle of Humankind at different points in time). In contrast, chimpanzees have an incidence rate of 47%, and gorillas as much as 90%, probably due to a diet with a much higher content of tough plants.
''P. robustus'' 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
Deciduous teeth or primary teeth, also informally known as baby teeth, milk teeth, or temporary teeth,Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 255 are the first set of teeth in the ...
and 14% of adult teeth were affected, in comparison to about 6.7% and 4.3%, respectively, for the combined teeth of ''A. africanus'', ''
A. sediba
''Australopithecus sediba'' is an extinct species of australopithecine recovered from Malapa Cave, Cradle of Humankind, South Africa. It is known from a partial juvenile skeleton, the holotype MH1, and a partial adult female skeleton, the par ...
'', early ''Homo'', and ''H. naledi''. The condition of these holes covering the entire tooth is consistent with the modern human ailment
amelogenesis imperfecta
Amelogenesis imperfecta (AI) is a congenital disorder which presents with a rare abnormal formation of the enamel or external layer of the crown of teeth, unrelated to any systemic or generalized conditions. Enamel is composed mostly of mineral, ...
. Since circular holes in enamel coverage are uniform in size, only present on the
molar teeth
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone t ...
, and have the same severity across individuals, the PEH may have been a genetic condition. It is possible that the
coding region
The coding region of a gene, also known as the coding sequence (CDS), is the portion of a gene's DNA or RNA that codes for protein. Studying the length, composition, regulation, splicing, structures, and functions of coding regions compared to no ...
concerned with thickening enamel also increased the risk of developing PEH.
As many as four ''P. robustus'' individuals have been identified as having had dental
cavities
Cavity may refer to:
Biology and healthcare
*Body cavity, a fluid-filled space in many animals where organs typically develop
**Gastrovascular cavity, the primary organ of digestion and circulation in cnidarians and flatworms
*Dental cavity or too ...
, indicating a rate similar to non-agricultural modern humans (1–5%). This is odd as ''P. robustus'' is thought to have had a diet high in gritty foods, and gritty foods should decrease cavity incidence rate, so ''P. robustus'' may have often consumed high-sugar cavity-causing foods. PEH may have also increased susceptibility to cavities. A molar from Drimolen showed a cavity on the tooth root, a rare occurrence in fossil great apes. In order for cavity-creating bacteria to reach this area, the individual would have also presented either alveolar resportion, which is commonly associated with
gum disease
Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main caus ...
; or super-eruption of the tooth which occurs when it becomes worn down and has to erupt a bit more in order to maintain a proper bite, exposing the root in the process. The latter is most likely, and the exposed root seems to have caused
hypercementosis
Hypercementosis is an idiopathic, non-neoplastic condition characterized by the excessive buildup of normal cementum (calcified tissue) on the roots of one or more teeth. A thicker layer of cementum can give the tooth an enlarged appearance, which ...
to anchor the tooth in place. The cavity seems to have been healing, possibly due to a change in diet or mouth microbiome, or the loss of the adjacent molar.
In a sample of 15 ''P. robustus'' specimens, all of them exhibited mild to moderate alveolar bone loss resulting from periodontal disease (the wearing away of the bone which supports the teeth due to gum disease). In contrast, in a sample of 10 ''A. africanus'' specimens, three exhibited no pathologies of the alveolar bone. Measuring the distance between the alveolar bone and the
cementoenamel junction
The cementoenamel junction, frequently abbreviated as the CEJ, is a slightly visible anatomical border identified on a tooth. It is the location where the enamel, which covers the anatomical crown of a tooth, and the cementum, which covers the ...
, ''P. robustus'' possibly suffered from a higher rate of tooth-attachment loss, unless ''P. robustus'' had a higher cervical height (the slightly narrowed area where the crown meets the root) in which case these two species had the same rate of tooth-attachment loss. If the former is correct, then the difference may be due to different dietary habits, chewing strategies, more pathogenic mouth microflora in ''P. robustus'', or some immunological difference which made ''P. robustus'' somewhat more susceptible to gum disease.
While removing the
matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** ''The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
encapsulating TM 1517, Schepers noted a large rock, which would have weighed , which had driven itself into the braincase through the
parietal bone
The parietal bones () are two bones in the Human skull, skull which, when joined at a fibrous joint, form the sides and roof of the Human skull, cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, an ...
. He considered this evidence that another individual had killed TM 1517 by launching the rock as a projectile in either defense or attack, but the most parsimonious explanation is that the rock was deposited during the fossilisation process after TM 1517 had died. In 1961, science writer
Robert Ardrey
Robert Ardrey (October 16, 1908 – January 14, 1980) was an American playwright, screenwriter and science writer perhaps best known for ''The Territorial Imperative'' (1966). After a Broadway and Hollywood career, he returned to his academic tr ...
noted two small holes about 2.5 cm (an inch) apart on the child skullcap SK 54, and believed this individual had been killed by being struck twice on the head in an assault; in 1970, Brain reinterpreted this as evidence of a
leopard attack
Leopard attacks are attacks inflicted upon humans, other leopards and other animals by the leopard. The frequency of leopard attacks on humans varies by geographical region and historical period. Despite the leopard's (''Panthera pardus'') extensi ...
.
Palaeoecology
The Pleistocene Cradle of Humankind was mainly dominated by the
springbok
The springbok (''Antidorcas marsupialis'') is a medium-sized antelope found mainly in south and southwest Africa. The sole member of the genus ''Antidorcas'', this bovid was first described by the German zoologist Eberhard August Wilhelm v ...
''Antidorcas recki'', but other antelope,
giraffes
The giraffe is a large African hoofed mammal belonging to the genus ''Giraffa''. It is the tallest living terrestrial animal and the largest ruminant on Earth. Traditionally, giraffes were thought to be one species, ''Giraffa camelopardalis ...
, and
elephants
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae and ...
were also seemingly abundant megafauna. The carnivore assemblage comprises the
sabertoothed cat
Machairodontinae is an extinct subfamily of carnivoran mammals of the family Felidae (true cats). They were found in Asia, Africa, North America, South America, and Europe from the Miocene to the Pleistocene, living from about 16 million until ...
s ''
Dinofelis
''Dinofelis'' is a genus of extinct sabre-toothed cats belonging to the tribe Metailurini or possibly Smilodontini. They were widespread in Europe, Asia, Africa and North America at least 5 million to about 1.2 million years ago (Early Pliocene t ...
spp.'' and ''
Megantereon
''Megantereon'' was a genus of prehistoric machairodontine saber-toothed cat that lived in North America, Eurasia, and Africa. It may have been the ancestor of ''Smilodon''.
Taxonomy
Fossil fragments have been found in Africa, Eurasia, and No ...
spp.'', and the hyena '' Lycyaenops silberbergi''. Overall, the animal assemblage of the region broadly indicates a mixed, open-to-closed landscape featuring perhaps
montane grasslands and shrublands
Montane grasslands and shrublands is a biome defined by the World Wildlife Fund. The biome includes high elevation grasslands and shrublands around the world. The term "montane" in the name of the biome refers to "high elevation", rather than th ...
. Australopithecines and early ''Homo'' likely preferred cooler conditions than later ''Homo'', as there are no australopithecine sites that were below in elevation at the time of deposition. This would mean that, like chimps, they often inhabited areas with an average diurnal temperature of , dropping to at night.
''P. robustus'' also cohabited the Cradle of Humankind with ''H. ergaster''/''H. erectus''. In addition, these two species resided alongside ''Australopithecus sediba'' which is known from about 2 million years ago at
Malapa
Malapa is a fossil-bearing cave located about northeast of the well known South African hominid-bearing sites of Sterkfontein and Swartkrans and about north-northwest of Johannesburg, South Africa. It is situated within the Cradle of Human ...
. The most recent ''A. africanus'' specimen, Sts 5, dates to about 2.07 million years ago, around the arrival of ''P. robustus'' and ''H. erectus''. It has been debated whether or not ''P. robustus'' would have had symbiotic, neutral, or antagonist relations with contemporary ''Australopithecus'' and ''Homo''. It is possible that South Africa was a refugium for ''Australopithecus'' until about 2 million years ago with the beginning of major climatic variability and volatility, and potentially competition with ''Homo'' and ''Paranthropus''.
Fossil-bearing deposits
;Swartkrans
At Swartkrans, ''P. robustus'' has been identified from Members 1–3. ''Homo'' is also found in these deposits, but species identification in Members 1 and 2 is debated between ''H. ergaster/H. erectus'', ''
H. habilis
''Homo habilis'' ("handy man") is an extinct species of archaic human from the Early Pleistocene of East and South Africa about 2.31 million years ago to 1.65 million years ago (mya). Upon species description in 1964, ''H. habilis'' was highly c ...
'', ''
H. rudolfensis
''Homo rudolfensis'' is an extinct species of archaic human from the Early Pleistocene of East Africa about 2 million years ago (mya). Because ''H. rudolfensis'' coexisted with several other hominins, it is debated what specimens can be confiden ...
'', or multiple species. In total, over 300 ''P. robustus'' specimens representing over 130 individuals, predominantly isolated teeth, have been recovered from Swartkrans.
Member 1 and Member 3 have several mammal species in common, making dating by animal remains (
biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...
) yield overlapping time intervals. Like the East African Olduvai Bed I (2.03–1.75 million years ago) and Lower Bed II (1.75–1.70 million years ago), Member 1 preserved the antelope '' Parmularius angusticornis'', the
wildebeest
Wildebeest ( , , ), also called gnu ( or ), are antelopes of the genus ''Connochaetes'' and native to Eastern and Southern Africa. They belong to the family Bovidae, which includes true antelopes, cattle, goats, sheep, and other even-to ...
Hamadryas baboon
The hamadryas baboon (''Papio hamadryas'' ) is a species of baboon within the Old World monkey family. It is the northernmost of all the baboons, being native to the Horn of Africa and the southwestern region of the Arabian Peninsula. These re ...
and ''
Dinopithecus
''Dinopithecus'' ("terrible ape") is an extinct genus of very large primate closely related to the baboon that lived during the Pliocene to the Pleistocene epoch of South Africa and Ethiopia. It was named by British paleontologist Robert Broom i ...
'' could mean Members 1–3 were deposited 1.9–1.65 million years ago, though the presence of
warthog
''Phacochoerus'' is a genus in the family Suidae, commonly known as warthogs (pronounced ''wart-hog''). They are pigs who live in open and semi-open habitats, even in quite arid regions, in sub-Saharan Africa. The two species were formerly cons ...
s suggests some sections of the deposits could date to after 1.5 million years ago.
Uranium–lead dating
Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routi ...
reports intervals of 3.21–0.45 million years ago for Member 1 (a very large error range), 1.65–1.07 million years ago for Member 2, and 1.04–0.62 million years ago for Member 3, though more likely the younger side of the estimate; this could mean ''P. robustus'' outlived ''P. boisei''.
Cosmogenic nuclide
Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the nucleus of an ''in situ'' Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom ( ...
geochronology has reported much more constrained dates of 2.2–1.8 million years ago for Member 1, and 0.96 million years ago for Member 3. No suitable section of Member 2 could be identified to date.
;Sterkfontein
At Sterkfontein, only the specimens StW 566 and StW 569 are firmly assigned to ''P. robustus'', coming from the "Oldowan infill" dating to 2–1.7 million years ago in a section of Member 5. Earlier members yielded ''A. africanus''. In 1988, palaeoanthropologist
Ronald J. Clarke
Ronald John Clarke is a paleoanthropologist most notable for the discovery of " Little Foot", an extraordinarily complete skeleton of ''Australopithecus'', in the Sterkfontein Caves. A more technical description of various aspects of his descr ...
suggested
StW 505
StW 505 is the most complete hominin cranium discovered in Sterkfontein Member 4 since Broom's excavations. It was found ''in situ'' in Member 4 breccia in 1989 and is larger, on the whole, than any other cranium from Sterkfontein that has compar ...
from the earlier Member 4 was an ancestor to ''P. robustus''. The specimen is still generally assigned to ''A. africanus'', though the Sterkfontein hominins are known to have an exceedingly wide range of variation, and it is debated whether or not the materials represent multiple species instead of just ''A. africanus''.
The appearance of the baboon ''
Theropithecus oswaldi
''Theropithecus oswaldi'' is an extinct species of '' Theropithecus'' from the early to middle Pleistocene of Kenya, Ethiopia, Tanzania, South Africa, Spain, Morocco and Algeria. It appears to have been a specialised grazer. The species went exti ...
'',
zebra
Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped coats. There are three living species: the Grévy's zebra (''Equus grevyi''), plains zebra (''E. quagga''), and the mountain zebra (''E. zeb ...
s,
lion
The lion (''Panthera leo'') is a large Felidae, cat of the genus ''Panthera'' native to Africa and India. It has a muscular, broad-chested body; short, rounded head; round ears; and a hairy tuft at the end of its tail. It is sexually dimorphi ...
s,
ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
es,
springhare
''Pedetes'' is a genus of rodent, the springhares, in the family Pedetidae. Members of the genus are distributed across southern and Eastern Africa.
Species
A number of species both extant and extinct are classified in the genus ''Pedetes''. ...
s, and several grazing antelope in Member 5 indicates the predominance of open grasslands, but sediment analysis indicates the cave opening was moist during deposition, which could point to a well-watered wooded grassland.
;Kromdraai
At Kromdraai, ''P. robustus'' has been unearthed at Kromdraai B, and almost all ''P. robustus'' fossils discovered in the cave have been recovered from Member 3 (out of 5 members). A total of 31 specimens representing at least 17 individuals have been recovered. The only potential ''Homo'' specimen from Member 3 is KB 5223, but its classification is debated. The ear bones of the juvenile KB 6067 from Member 3 is consistent with that of ''P. robustus'', but the dimensions of the
cochlea
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...
and
oval window
The oval window (or ''fenestra vestibuli'' or ''fenestra ovalis'') is a membrane-covered opening from the middle ear to the cochlea of the inner ear.
Vibrations that contact the tympanic membrane travel through the three ossicles and into the in ...
better align with the more ancient StW 53 from Sterkfontein Member 4 with undetermined species designation. KB 6067, therefore, may possibly be basal to (more ancient than) other ''P. robustus'' specimens, at least those for which ear morphology is known.
Palaeomagnetism
Paleomagnetism (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.''
Certain magnetic minerals in rocks ...
suggests Member 3 may date to 1.78–1.6 million years ago, Member 2 to before 1.78 million years ago, and Member 1 to 2.11–1.95 million years ago.
The animal remains of Kromdraai A suggest deposition occurred anywhere between 1.89 and 1.63 million years ago, and the presence of Oldowan or Achulean tools indicates early ''Homo'' activity. The biostratigraphic dating of Kromdraai B is less clear as there are no animal species which are known to have existed in a narrow time interval, and many non-hominin specimens have not been assigned to a species (left at genus level). About 75% of mammalian remains other than ''P. robustus'' are monkeys, including leaf-eating
colobine monkey
The Colobinae or leaf-eating monkeys are a family (biology), subfamily of the Old World monkey family that includes 61 species in 11 genus, genera, including the black-and-white colobus, the large-nosed proboscis monkey, and the gray langurs. So ...
s, possibly the earliest record of the Hamadryas baboon, ''
Gorgopithecus
''Gorgopithecus'' ("fierce ape" from Ancient Greek γοργος (gorgos), "fierce" + πίθηκος (píthēkos), "ape") is an extinct genus of primate, in the old word monkey family Cercopithecidae, closely related to the baboons.
There is only o ...
'', and ''
Papio angusticeps
Baboons are primates comprising the biology, genus ''Papio'', one of the 23 genera of Old World monkeys. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow baboon, the Kinda baboon and the ...
'' in South Africa. The absence of the baboons ''T. oswaldi'' and ''Dinopithecus'' could potentially mean Member 3 is older than Sterkfontein Member 5 and Swartkrans Member 1; which, if correct, would invalidate the results from palaeomagnetism, and make these specimens among the oldest representatives of the species.
;Gondolin Cave
Gondolin Cave has yielded 3 hominin specimens: a right third premolar assigned to early ''Homo'' (G14018), a partial left gracile australopithecine first or second molar (GDA-1), and a robust australopithecine second molar (GDA-2). The first hominin specimen (G14018) was found by German palaeontologist
Elisabeth Vrba
Elisabeth S. Vrba (born 17 May 1942) is a paleontologist at Yale University who developed the turnover-pulse hypothesis.
Education
Vrba earned her Ph.D. in Zoology and Palaeontology at the University of Cape Town, in 1974. Vrba studied zoology ...
in 1979, and the other two specimens were recovered in 1997 by, respectively, South African palaeoanthropologist
Andre Keyser
André Werner Keyser (8 March 1938, Pretoria – 15 August 2010, Pretoria), was a South African palaeontologist and geologist noted for his discovery of the Drimolen hominid site and of numerous hominid remains.
In 1994 he discovered a fema ...
and excavator L. Dihasu. GDA-2—measuring , an area of —is exceptionally large for ''P. robustus'', which has a recorded maximum of . This falls within the range of ''P. boisei'' , so the discoverers assigned it to an indeterminate species of ''Paranthropus'' rather than ''P. robustus''.
GDA-2 was found alongside the pig ''
Metridiochoerus andrewsi
''Metridiochoerus'' is an extinct genus in the pig family indigenous to the Pliocene and Pleistocene of Africa. It is also known as the giant warthog.
Description
''Metridiochoerus'' was a large animal, in length, resembling a giant warthog. ...
'', which means the tooth must be 1.9–1.5 million years old. Using this and palaeomagnetism, it may date to roughly 1.8 million years ago.
;Cooper's Cave
Cooper's Cave was first reported to yield ''P. robustus'' remains in 2000 by South African palaeoanthropologists Christine Steininger and
Lee Rogers Berger
Lee Rogers Berger (born December 22, 1965) is an American-born South African paleoanthropology, paleoanthropologist and National Geographic Explorer-in-Residence. He is best known for his discovery of the ''Australopithecus sediba'' type site, M ...
. Specimens include a crushed partial right face (COB 101), three isolated teeth, a juvenile jawbone, and several skull fragments.
The animal remains in the hominin-bearing deposit are similar to those of Swartkrans and Kromdraai A, so the Cooper's Cave deposits may date to 1.87–1.56 million years ago.
;Drimolen Cave
Drimolen Cave was first discovered to have yielded hominin remains by Keyser in 1992, who, in eight years, oversaw the recovery of 79 ''P. robustus'' specimens. Among these are the most complete ''P. robustus'' skulls: the presumed female DNH-7 (which also preserved articulated jawbone with almost all the teeth), and presumed male DNH 155. It was also associated with the ''H. ergaster''/''H. erectus'' skull DNH 134. The Drimolen material preserves several basal characteristics relative to the Swartkrans and Kromdraai remains (meaning it may be older).
The site is thought to be roughly 2–1.5 million years old based on animal remains which have also been recovered from Swartkrans Member 1. The animal assemblage is broadly similar to that of Cooper's Cave, meaning they probably are about the same age. In 2020, DNH 152 was palaeomagnetically dated to 2.04–1.95 million years ago, making it the oldest identified ''P. robustus'' specimen.
Predation
Australopithecine bones may have accumulated in caves due to large carnivores dragging in carcasses, which was first explored in detail by Brain in his 1981 book '' The Hunters or the Hunted?: An Introduction to African Cave Taphonomy''. The juvenile ''P. robustus'' skullcap SK 54 has two puncture marks consistent with the lower canines of the
leopard
The leopard (''Panthera pardus'') is one of the five extant species in the genus '' Panthera'', a member of the cat family, Felidae. It occurs in a wide range in sub-Saharan Africa, in some parts of Western and Central Asia, Southern Russia, a ...
specimen SK 349 from the same deposits. Brain hypothesised that ''Dinofelis'' and perhaps also
hunting hyena
''Chasmaporthetes'', also known as hunting or running hyena, is an extinct genus of hyenas distributed in Eurasia, North America, and Africa during the Pliocene-Pleistocene epochs, living from 4.9 million to 780,000 years ago, existing for about ...
s specialised on killing australopithecines, but carbon isotope analysis indicates these species predominantly ate large grazers, while the leopard, the sabertoothed ''Megantereon'', and the
spotted hyena
The spotted hyena (''Crocuta crocuta''), also known as the laughing hyena, is a hyena species, currently classed as the sole extant member of the genus ''Crocuta'', native to sub-Saharan Africa. It is listed as being of least concern by the IUC ...
were more likely to have regularly consumed ''P. robustus''. Brain was unsure if these predators actively sought them out and brought them back to the cave den to eat, or inhabited deeper recesses of caves and ambushed them when they entered. Modern-day baboons in this region often shelter in
sinkhole
A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as ''vrtače'' and shakeholes, and to openi ...
s especially on cold winter nights, though Brain proposed that australopithecines seasonally migrated out of the
Highveld
The Highveld (Afrikaans: ''Hoëveld'', where ''veld'' means "field") is the portion of the South African inland plateau which has an altitude above roughly 1500 m, but below 2100 m, thus excluding the Lesotho mountain regions to the south-east of ...
and into the warmer
Bushveld
The Bushveld (from af, bosveld, af, bos 'bush' and af, veld) is a tropical and subtropical grasslands, savannas, and shrublands, sub-tropical woodland ecoregion of Southern Africa. It encompasses most of Limpopo Province and a small part of ...
, only taking up cave shelters in spring and autumn.
As an antipredator behaviour, baboons often associate themselves with medium-to-large herbivores, most notably
impala
The impala or rooibok (''Aepyceros melampus'') is a medium-sized antelope found in eastern and southern Africa. The only extant member of the genus '' Aepyceros'' and tribe Aepycerotini, it was first described to European audiences by Germa ...
s, and it is possible that ''P. robustus'' as well as other early hominins which lived in open environments did so also, given they are typically associated with an abundance of medium-to-large bovid and horse remains.
Extinction
Though ''P. robustus'' was a rather hardy species with a tolerance for environmental variability, it seems to have preferred wooded environments, and similarly most ''P. robustus'' remains date to a wet period in South Africa 2–1.75 million years ago conducive to such biomes. The extinction of ''P. robustus'' coincided with the
Mid-Pleistocene Transition
The Mid-Pleistocene Transition (MPT), also known as the Mid-Pleistocene Revolution (MPR), is a fundamental change in the behaviour of glacial cycles during the Quaternary glaciations. The transition happened approximately 1.25–0.7 milli ...
, and the doubling of glacial cycle duration. During glacial events, with more ice locked up at the poles, the
tropical rain belt
Rainfall and the tropical climate dominate the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year, roughly following the solar equator. The tropical rain belt is an area of active rain that i ...
contracted towards the equator, subsequently causing the retreat of wetland and woodland environments. Before the transition, ''P. robustus'' populations possibly contracted to certain wooded refuge zones over 21,000-year cycles, becoming regionally extinct in certain areas until the wet cycle whereupon it would repopulate those zones. The continual prolonging of dry cycles may have caused its extinction, with the last occurrence in the fossil record 1–0.6 million years ago (though more likely 0.9 million years ago). ''Homo'' possibly was able to survive by inhabiting a much larger geographical range, more likely to find a suitable refuge area during unfavourable climate swings.
However, the geographical range of ''P. robustus'' in the fossil record is roughly , whereas the critically endangered
eastern gorilla
The eastern gorilla (''Gorilla beringei'') is a critically endangered species of the genus ''Gorilla'' and the largest living primate. At present, the species is subdivided into two subspecies. There are 3,800 eastern lowland gorillas or Graue ...
(with the smallest range of any African ape) inhabits , the critically endangered
western gorilla
The western gorilla (''Gorilla gorilla'') is a great ape found in Africa, one of two species of the hominid genus ''Gorilla''. Large and robust with males weighing around , the hair is significantly lighter in color than the eastern gorilla, '' ...
, and the
endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inva ...
chimpanzee . Therefore, fossil distribution very unlikely represents the true range of the species; consequently, ''P. robustus'' possibly went extinct much more recently somewhere other than the Cradle of Humankind (
Signor–Lipps effect
The Signor–Lipps effect is a paleontological principle proposed in 1982 by Philip W. Signor and Jere H. Lipps which states that, since the fossil record of organisms is never complete, neither the first nor the last organism in a given taxon w ...
John D. Hawks
John Hawks is an associate professor of anthropology at the University of Wisconsin–Madison. He also maintains a paleoanthropology blog. Contrary to the common view that cultural evolution has made human biological evolution insignificant, H ...