Australopithecus in the context of Humans

Homo (from Latin homō 'human') is a genus of great ape (family Hominidae) that emerged from the early homininian genus Australopithecus, encompassing a single extant species, Homo sapiens (modern humans), along with a number of extinct species (e.g. Homo erectus and Homo neanderthalensis) classified as either ancestral or closely related to modern humans, collectively called archaic humans. Homo, together with the genus Paranthropus, is probably most closely related to the species Australopithecus africanus within Australopithecus. The closest living relatives of Homo are of the hominin genus Pan (chimpanzees and bonobos), with the ancestors of Pan and Homo estimated to have diverged around 5.7–11 million years ago during the Late Miocene.

The oldest member of the genus is Homo habilis, with fossil records of just over 2 million years ago. H. erectus appeared about 2 million years ago and spread throughout Africa (debatably as another species called Homo ergaster) and Eurasia in several migrations. The species was adaptive and successful, and persisted for more than a million years before gradually diverging into new species around 500,000 years ago.

The australopithecines (/ɒˈstrəloʊˈpɪθəsiːnz, ˈɔːstreɪloʊ-/), formally Australopithecina or Hominina, are generally any species in the related genera of Australopithecus and Paranthropus. It may also include members of Kenyanthropus, Ardipithecus, and Praeanthropus. The term comes from a former classification as members of a distinct subfamily, the Australopithecinae. They are classified within the Australopithecina subtribe of the Hominini tribe. These related species are sometimes collectively termed australopithecines, australopiths, or homininians. They are the extinct, close relatives of modern humans and, together with the extant genus Homo, comprise the human clade. There is no general agreement to whether australopithecines are closest relatives of modern humans, as it has been argued that they are more closely related to extant African apes. Members of the human clade, i.e. the Hominini after the split from the chimpanzees, are called Hominina (see Hominidae; terms "hominids" and hominins).

While none of the groups normally directly assigned to this group survived, the australopithecines do not appear to be literally extinct (in the sense of having no living descendants) as the genera Kenyanthropus, Paranthropus, and Homo probably emerged as sisters of a late Australopithecus species such as A. africanus and/or A. sediba.

Paranthropus is a genus of extinct hominin which contains two widely accepted species: P. robustus and P. boisei. However, the validity of Paranthropus is contested, and it is sometimes considered to be synonymous with Australopithecus. They are also referred to as the robust australopithecines. They lived between approximately 2.9 and at least 1 million years ago (mya) from the end of the Pliocene to the Middle Pleistocene.

Paranthropus is characterised by robust skulls, with a prominent gorilla-like sagittal crest along the midline—which suggest strong chewing muscles—and broad, herbivorous teeth used for grinding. However, they likely preferred soft food over tough and hard food. Typically, Paranthropus species were generalist feeders, but while P. robustus was likely an omnivore, P. boisei seems to have been herbivorous, possibly preferring abundant bulbotubers. Paranthropoids were bipeds. Despite their robust heads, they had comparatively small bodies. Average weight and height are estimated to be 40 kg (88 lb) at 132 cm (4 ft) for P. robustus males, 50 kg (110 lb) at 137 cm (4 ft 6 in) for P. boisei males, 32 kg (71 lb) at 110 cm (3 ft 7 in) for P. robustus females, and 34 kg (75 lb) at 124 cm (4 ft 1 in) for P. boisei females.

Homo habilis (lit. 'handy man') is an extinct species of archaic human from the Early Pleistocene of East and South Africa about 2.4 million years ago to 1.65 million years ago (mya). It is among the oldest species of archaic humans. Suggestions for pushing back the age to 2.8 Mya were made in 2015 based on the discovery of a jawbone. Upon species description in 1964, H. habilis was highly contested, with many researchers recommending it be synonymised with Australopithecus africanus, the only other early hominin known at the time, but H. habilis received more recognition as time went on and more relevant discoveries were made. By the 1980s, H. habilis was proposed to have been a human ancestor, directly evolving into Homo erectus, which directly led to modern humans. This viewpoint is now debated. Several specimens with insecure species identification were assigned to H. habilis, leading to arguments for splitting, namely into "H. rudolfensis" and "H. gautengensis" of which only the former has received wide support.

H. habilis brain size generally varied from 500 to 900 cm (31–55 cu in). The body proportions of H. habilis are only known from two highly fragmentary skeletons, and is based largely on assuming a similar anatomy to the earlier australopithecines. Because of this, it has also been proposed H. habilis be moved to the genus Australopithecus as Australopithecus habilis. However, the interpretation of H. habilis as a small-statured human with inefficient long-distance travel capabilities has been challenged. The presumed female specimen OH 62 is traditionally interpreted as having been 100–120 cm (3 ft 3 in – 3 ft 11 in) in height and 20–37 kg (44–82 lb) in weight assuming australopithecine-like proportions, but assuming humanlike proportions she would have been about 148 cm (4 ft 10 in) and 35 kg (77 lb). Nonetheless, Homo habilis may have been at least partially arboreal like what is postulated for australopithecines. Early hominins are typically reconstructed as having thick hair and marked sexual dimorphism with males much larger than females, though relative male and female size is not definitively known.

Ardipithecus is a genus of an extinct hominine that lived during the Late Miocene and Early Pliocene epochs in the Afar Depression, Ethiopia. Originally described as one of the earliest ancestors of humans after they diverged from the chimpanzees, the relation of this genus to human ancestors and whether it is a hominin is now a matter of debate. Two fossil species are described in the literature: A. ramidus, which lived about 4.4 million years ago during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago (late Miocene). Initial behavioral analysis indicated that Ardipithecus could be very similar to chimpanzees; however, more recent analysis based on canine size and lack of canine sexual dimorphism indicates that Ardipithecus was characterised by reduced aggression, and that they more closely resemble bonobos.

Some analyses describe Australopithecus as being sister to Ardipithecus ramidus specifically. This means that Australopithecus is distinctly more closely related to Ardipithecus ramidus than Ardipithecus kadabba. Cladistically, then, Australopithecus (and eventually Homo sapiens) indeed emerged within the Ardipithecus lineage, and this lineage is not literally extinct.

Sterkfontein (Afrikaans for Strong Spring) is a set of limestone caves of special interest in paleoanthropology located in Gauteng province, about 40 kilometres (25 mi) northwest of Johannesburg, South Africa, in the Muldersdrift area close to the town of Krugersdorp. The archaeological sites of Swartkrans and Kromdraai are in the same area. Sterkfontein is a South African National Heritage Site and was also declared a World Heritage Site in 2000. The area in which it is situated is known as the Cradle of Humankind. The Sterkfontein Caves are also home to numerous wild African species including Belonogaster petiolata, a wasp species of which there is a large nesting presence.

Numerous early hominin remains have been found at the site over the last few decades. These have been attributed to Australopithecus, early Homo and Paranthropus.

Australopithecus anamensis is a hominin species that lived roughly between 4.3 and 3.8 million years ago, and is the oldest known Australopithecus species.

Nearly 100 fossil specimens of A. anamensis are known from Kenya and Ethiopia, representing over 20 individuals. The first fossils of A. anamensis discovered are dated to around 3.8 and 4.2 million years ago and were found in Kanapoi and Allia Bay in northern Kenya.

Paranthropus robustus is a species of robust australopithecine from the Early and possibly Middle Pleistocene of the Cradle of Humankind, South Africa, about 2.27 to 0.87 (or, more conservatively, 2 to 1) million years ago. It has been identified in Kromdraai, Swartkrans, Sterkfontein, Gondolin, Cooper's, and Drimolen Caves. Discovered in 1938, it was among the first early hominins described, and became the type species for the genus Paranthropus. However, it has been argued by some that Paranthropus is an invalid grouping and synonymous with Australopithecus, 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 forces, as well as inflated cheek teeth (molars and premolars). Males had more heavily built skulls than females. P. robustus may have had a genetic susceptibility for pitting enamel hypoplasia on the teeth, and seems to have had a dental cavity rate similar to non-agricultural modern humans. The species is thought to have exhibited marked sexual dimorphism, with males substantially larger and more robust than females. Based on 3 specimens, males may have been 132 cm (4 ft 4 in) tall and females 110 cm (3 ft 7 in). Based on 4 specimens, males averaged 40 kg (88 lb) in weight and females 30 kg (66 lb). 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 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 (movement in the trees).

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

Robust australopithecines are characterised by heavily built skulls capable of producing high stresses and bite forces, and some of the largest molars with the thickest enamel of any known ape. P. boisei is the most robust of this group. Brain size was about 450–550 cc (27–34 cu in), similar to other australopithecines. Some skulls are markedly smaller than others, which is taken as evidence of sexual dimorphism where females are much smaller than males, though body size is difficult to estimate given only one specimen, OH 80, definitely provides any bodily elements. The presumed male OH 80 may have been 156 cm (5 ft 1 in) tall and 61.7 kg (136 lb) in weight, and the presumed female KNM-ER 1500 124 cm (4 ft 1 in) tall (though its species designation is unclear). The arm and hand bones of OH 80 and KNM-ER 47000 suggest P. boisei was arboreal to a degree.

Makapansgat (/mʌkʌˈpʌnsxʌt/) (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 limeworks containing Australopithecus-bearing deposits dating to between 3.0 and 2.6 million years BP. The whole Makapan Valley has been declared a South African Heritage Site. Makapansgat belongs to the Cradle of Humankind.

"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 museum collection were sufficient to ascertain that the individual had been able to walk upright, the remainder of the skeleton was, subsequently, located in the cave from which the ankle bones had been collected.

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 confidently assigned to this species beyond the lectotype skull KNM-ER 1470 and other partial skull aspects. No bodily remains are definitively assigned to H. rudolfensis. Consequently, both its generic classification and validity are debated without any wide consensus, with some recommending the species to actually belong to the genus Australopithecus as A. rudolfensis or Kenyanthropus as K. rudolfensis, or that it is synonymous with the contemporaneous and anatomically similar H. habilis.

H. rudolfensis is distinguished from H. habilis by larger size, but it is also argued that this species actually consists of male H. habilis specimens, assuming that H. habilis was sexually dimorphic and males were much larger than females. Because no bodily remains are definitely identified, body size estimates are largely based on the stature of H. habilis. Using this, male H. rudolfensis may have averaged about 160 cm (5 ft 3 in) in height and 60 kg (130 lb) in weight, and females 150 cm (4 ft 11 in) and 51 kg (112 lb). KNM-ER 1470 had a brain volume of about 750 cc (46 cu in). Like other early Homo, H. rudolfensis had large cheek teeth and thick enamel.