Australopithecus

Male. Credit: John Gurche.

*Australopithecus* is an extinct genus of australopithecine hominid that lived in South Africa from the Middle Pliocene to the Early Pleistocene.

## History

The first and type specimen of *Australopithecus* was found in 1924 in a lime quarry. When workers found a skull in Taung, South Africa, it was excavated and studied by Raymond Dart of the University of the Witwatersrand in Johannesburg. He named it *Australopithecus africanus*; of a three-year-old bipedal primate. In February 1925, the skull was featured in Nature, where Dart would realize it bore many humanoid features, and concluded it to be an early hominin. Later, Scottish Robert Broom and Dart set to discover more specimens like the Taung Child, discovering several *A. africanus* specimens from various sites. Initially, anthropologists were hostile towards the idea that *Australopithecus* was anything but an ape, until the popular consensus had changed in the 1940s.

Ernst Walter Mayr in 1950 stated all bipedal apes were of *Homo*, wanting to synonymize *A. africanus* with *Homo transvaalensis*. However, Robinson in 1954 had the opposite view, and excluding *Australopithecus* from *Homo* became popular. Mary Leakey in 1959 discovered the first australopithecine in eastern Africa was an *A. boisei* from Olduvai Gorge, Tanzania. Since then, Leakey and her family have further excavated the locality, discovering australopiths, *Homo erectus* and *Homo habilis*. Scientists took 20 years to accept *Australopithecus* as a hominin. *A. africanus* was proposed as the first evidence that *Homo* evolved in Africa, as Darwin has hypothesized in 1871 in The Descent of Man. However, Dart claimed that the Taung child was a transitional stage of an early hypothesis that modern traits such as brain size were developed early on, with the latter evolving before bipedalism. Thus, *A. africanus* was placed nearer to *Pan* or *Gorilla*, mostly by SIr Arthur Keith. Charles Dawson's Piltdown Man hoax later perpetuated this, with the *Homo erectus* Peking Man leading most to assume *Homo* evolved. Modern morphology was chalked up to ontogeny, but Dart and Broom continued to argue for a phylogenetic position far from chimpanzees. Dart noted many large mammal bones in australopithecine-bearing caves, now attributable to hyenas, were proposed by Dart to be what he called the "osteodontokeratic culture"; used by australopithecine hunters who manufactured weapons from long bones, teeth and horns of ungulates, described as:

—Dart's explanation of the osteodontokeratic culture

Broom and Gerrit Willem Hendril Schepers (1946) published a detailed monograph and Sir Willfried Le Gros Clark published a flurry of papers, earning wide support for *A. africanus* as a human ancestor. In 1947, Mrs. Ples, the most complete skull, was accepted as valid and prompted research on the Piltdown Man, revealing it was a fraud. Dart (1949) recommended splitting a presumed female face fragment from Makapansgat, MLD 2, into "A. prometheus", referring a jaw from the same site in 1954, However, John Talbot Robinson (1953) believes such small details do not distinguish it and that otherwise they are indistinguishable. In 1955, Dart agreed with synonymization, finding cross-continental speciation unlikely to occurr over several tens of kilometers. Ronald J. Clarke (2008) revived "A. prometheus" to house StW 573, "Little Foot", StS 71, StW 505, StW 183, StW 498, StW 384, StS 1 and MLD 2. Lee Berger and John Hawks (2018) suggested that the name was a nomen nudum based on improper description and no autapomorphies. At the time they were 3.3 million years old but redating by Kathleen Kuman and Clarke (2019) found StW 573 to be 3.67 million years old. The age of the Sterkfontein fossils have an unresolved age. Little Foot is the most complete early hominin, being 90% complete.

*A. africanus* from Gladsvale was also discovered, with it Gladysvale and Makapansgat all being localities from the Cradle of Humankind. Mrs. Ples and 2 partial specimens are reported from Sterkfontein Member 4 from 2.8-2.15 million years ago. This would make it the most abundant deposit to present *Australopithecus*. However, it is debated it the remains of these assigned to "A. prometheus" can be distinguished from the typical *A. africanus*. *A. anamensis*, *A. afarensis* and *A. bahrelghazali* were all split into *Praeanthropus*, which has been dismissed since. However, Dembo et al. (2015) uses phylogenetic data to find that *"A." afarensis* and *"A." garhi* form a clade. Since the name was used before, *Praeanthropus* should therefore be resurrected to house these and *A. africanus* should remain in *Australopithecus*, making the genus monotypic.

## Description

From a four-specimen dataset, *A. africanus* had a cranial capacity averaging 420-510, with an estimated neonatal capacity of 165.5-190 using adults and juveniles of modern primates. This would indicate birth with about 38% of the brain; which is more similar to the 40% of other apes and the 30% in humans. The inner ear bore wide semicircular canals like other apes, with loose turns at the termination point of the cochlea. This may reflect habitual tree climbing and bipedal walking, since the inner ear reflects the vestibular system and thus balance. The jaw was prognathic and the face was somewhat dished with a defined brow. The temporal lines ran across both sides of the braincase and raised on small crests. The canines are reduced, though still relatively large, with large cheek teeth and thick enamel. The third molar of the upper jaw is the largest molar and the second molar in the lower jaw is the largest. It bore a fast, ape-like development rate. Clarke suggests that "A. prometheus", while older, is distinguished by larger and bulbous cheek teeth, larger incisors and canines, projecting cheeks, wider spaced orbits and a sagittal crest. *A. afarensis* bears great variation and high sexual dimorphism, so these traits are deemed irrelevant by most.

Henry McHenry (1992) estimated an average weight of 40.8 or 52.8 kilograms (90 or 116 pounds) assuming modern bodily proportions based on 5 partial skeletons and 30.2 or 36.8 kilograms (67 or 81 pounds) for females. William L. Jungers et al. (2015) reported a similar average weight without trying to distinguish sex of 30.7 kilograms and a range of 22.8-43.3 kilograms based on 19 specimens. Based on 7 specimens, McHenry estimated males were 138 centimeters (4 feet 6 inches) tall and females 125 centimeters (4 feet 1 inch). Manuel Will et al. (2017) used 24 specimens to extrpolate a height of 124.4 centimeters and a range of 110-142 centimeters (3-4 feet 4-8 inches). StW 573 is was likely an elder woman who was estimated to be 130 centimeters (4 feet 3 inches) tall. The clavicle is quite long with a similar absolute length to humans. 7 cervicals, 12 thoracic and 5 lumbar vertebrae were present. StW 573 has an atlas with mechanical advantages for the muscles who move the shoulder girdle as in chimpanzees and gorillas, possibly indicating less lordosis in *A. africanus* cervicals. The L3-5 curves outwards in StS 14, like modern women, and straighter in StW 431 in modern men. This likely reflects reinforcement of the spine during pregnancies, and StS 14 preserves a somewhat complete pelvis showing that the sacrum was relatively flat and oriented further backwards like in Lucy (*Praeanthropus afarensis*) and the pelvic cavity was overall platypelloid in shape. This may indicate a broad birth canal compared to neonate head size and thus non-rotational birth. However this is still debated. The angle between the sacrum and the lumbar vertebrae is about 148.7° when standing, which would indicate a posture not as erect.

*A. africanus* bore mosaic anatomy in the hand, with it being unclear if the species was arboreal or not. However, the upper limbs are more ape-like and interpreted to a certain extent as arboreal. The fingers are curved, the shoulders shrugged and the arms relatively long, which are interpeted as arboreal traits, with the shoulder most like *Pongo*, suited for continuous stability and weight bearing while hanging overhead. The right clavicle of StW 573 has a sigmoid curve like *Homo sapiens*, which indicates modern stabilizing of the shoulder against the humerus. Powerful climbing muscles are inferred from known arm material. The brachial index is 82.8-86.2, midway between *Pan troglodytes* and *Homo sapiens*, indicating forearm reduction from ancient forms such as *Ardipithecus ramidus*. A humanlike thumb and wrist grant precision grip and forceful opposition between the thumb and the fingers, which is typically interpreted as an adaptation for tool making at the expense of efficient climbing and arboreality. The legs were adapted for habitual bipedalism, though some parts of the tibia are ape-like and could represent musclulature that had not fully reorganized, though this has unclear implications. The trabecular at the hip is very modern, which would have made climbing and the hip loading it produces inconsistent. The tibia met the foot at a similar angle to *Homo sapiens*, which is necessary to habitual bipedalism. Thus the ankle was not adept for climbing. However, the Twa hunter-gatherers of the Congo can achieve a chimpanzee-like angle while climbing through longer gastrocnemius fibers rather than their skeleton. Somewhat ape-like ankle morphology may have affected walking. Foot elementsare mostly known from Sterkfontein Member 4, revealing a modern stiff midfoot and a lack of a midtarsal break. Though *A. africanus* had a big toe that was adducted like humans, it likely did not push off from this toe, likely using the side foot instead, StW 573 is the oldest specimen with an adducted big toe and StW 355 has the most curved proximal foot phalanx of any hominin, similar to orangutans and siamangs. StW had arms about 53.4 centimeters long and legs 61.5 centimeters long. This makes the arm ~86.9% of the leg length. This is the first hominin specimen to definitively show how the legs and arms were nearly equal in length and they were overall similar in proportion to non-human apes.

## Paleobiology

### Diet

Robinson (1954) proposed that it was a generalist omnivore, with Frederick E. Grine (1981) suggesting that it was specialized for soft foods, such as fruit and leaves. Carbon isotope analyses found it actually had a very variable diet of C4 savanna plants (grasses, seeds, rhizomes, underground storage organs and possibly grass-eating invertebrates such as locusts or termites), grazing, insectivorous or carnivorous. Most primates do not eat C4 plants. Facial anatomy suggests producing high stress in the premolars for eating small, hard objects such as nuts and seeds that need to be cracked by the teeth, or for processing much food at a time, though hard food consumption is often dismissed as fallback in lean times. They may have required hammerstones to crack nuts, possibly marula nuts, though it is not associated with tools and chimpanzees do the same. *A. africanus* lacks evidence of dental cavities, which would indicate that it either did not consume sugary foods often or frequently consumed gritty foods. However, the 2nd right permanent incisor of StW 270 and the right canine of StW 213 (the same individual) show lesions consistent with acid erosion, which indicates regularly biting into acidic foods such as citrus. However, tubers may have done the same if chewed with the front teeth. Barium continually deposits onto the teeth until 6-9 months, then decreases until 12, likely caused by breast milk and probably reflecting the weaning age. This is comparable to humans. Barium deposits them stall and restart cyclically for every day, for several years. In the first molar specimen, StS 28, they occurred every 6-9 months and every 4-6 months for the lower canine specimen StS 51. This carries for 4-5 years. Lithium and strontium also cyclically deposit, with barium, lithium and strontium bands occurring in primates and are caused by seasonal famine when a child heavily relies on nursing and less desirable fallback foods for sustenance. However, it is unknown is this could be extended for *Australopithecus*.

### Society

Though australopithecine sociality is difficult to estimate, a 2011 strontium isotope study on teeth from dolomite suggests that (assuming small teeth are females and the larger are males) females are more likely to leave their place of birth; similar to the dispersal patterns of modern hominins who have multi-male kinship-based society, rather than a harem society. The small canines of the males suggest a lower degree of male-male aggression than non-human apes. Males did not seem to travel far beyond the valley, which would indicate a small home range or that they preferred dolomitic landscapes, maybe due to abundant caves or possibly related to vegetation growth.

### Paleopathology

In a sample of 10, 7 specimens bore mild-to-moderate alveolar bone loss resulting from periodontal disease. StS 24a, a juvenile, was diagnosed with an extreme case of this on the right side of the mouth, which has caused pathological bone growth around the site, with movement of the first 2 right molars during cyclical periods of bacterial infection and the resulting inflammation. The individual appears to have preferred chewing on the left side. The disease would have severely hindered food processing, particularly in the last year of life, and this individual may have relied on peers to survive. Geoffrey Raymond Frisk and Gabriele Macho (1992) interpreted StW 363, an ankle, as having evidence for a healed calcneal fracture on the heel, which they believed may have resulted from falling from a tree. If they were correct, this would indicate that the individual survived long after the fall despite losing much of the left leg's function. However, they note that this damage may have been caused bu calcite deposition and crystallization during fossilization. These types of fractures are found in humans but mostly in arboreal primates.

### Conflict

    Underneath the pelvis of StW 573 ("Little Foot") lays a *Parapapio broomi* skull the size of a baboon, intermingled with vertebrae are two large thoracic vertebrae and next to the *Australopithecus* femur is a radius. Cercopithecoid remains are known from Member 2, some close to the hominin, but the large (possibly male) *Parapapio* leads authors to question how both apes died together. Near dolomite caves grow fig trees, which could have attracted the two apes to one-another. Similar circumstances occur in chimpanzees and baboons. It is possible the two fought, plummeting into Sterkfontein. This means that apes like *Australopithecus* came into contact with other primates.

## Species

* *A. africanus*
* *A. prometheus*? (=*A. africanus*?)

### Reassigned Species

* *"A." robustus*
* *"A." aethiopicus*
* *"A." platyops*
* *"A." boisei*
* *"A." palaeojavanicus*
* *"A." rudolfensis*
* "*A." habilis*
* "A. canadensis" ("bigfoot")
* *A. transvaalensis* (=*A. africanus*)
* *"A." anamensis*
* *"A." afarensis*
* *"A." bahrelghazali*
* *"A." sediba*
* *"A." deyiremedia*
* *"A." garhi*
* *"A." platyops*
* *A. africanus aethiopicus*
* *A. africanus afarensis*
* *A. africanus africanus*
* *A. africanus habilis*
* *A. africanus modjokertensis*
* *A. africanus robustus*
* *A. africanus tanzaniensis*
* *A. africanus transvaalensis*

## Synonyms

* *Plesianthropus*
* *Afaranthropus*
* *Homo guatengensis*
* *Astralpithecus* (lapsus)

## Notable Specimens

* File:Little foot.png  STW 573 "Little Foot": A nearly complete *A.* sp. indet. specimen excavated from a cave system in Sterkfontein. Excavation took 15 years, due to the bones embedded in concrete-like rock found in South Africa by Ronald J. Clarke from 1994-1998 . In 2021, the cranium was 3D synchrotron-scanned, revealing the following new information: hypoplasias in the enamel, incremental lines in the cementum, diploic channels in the microarchitecture of the skull bones and 3D spatially-organized Haversian channels in the mandibular symphasis .
* STS 5 "Mrs. Ples": An *A. africanus* skull found in Sterkfontien, Africa by Broom and Robinson on April 18, 1947 .
* STS 14: The partial skeleton of an *A. africanus*, possibly the same as STS 5, found in Sterkfontein by Broom and Robinson in August of 1947 .
* STS 71: A preserved *A. africanus* skull, possibly matching a jaw, STS 71 AND STS 36. Discovered in Sterkfontein by Robert Broom in 1947 .
* StW 505: Since Broom's excavations, one of the most complete hominin skulls found in the Sterkfontein Member 4. Possibly attributed to A. sp.. This specimen was found in 1989 .
* Taung 1 "Taung Child/Baby": This specimen represents the most important anthropological discovery of the 20th century, representing a 3.3 year-old *A. africanus*. Discovered by Raymond Dart in Taung, Africa in 1924, it was published as a new species, *A. africanus*.
* Stw 53: A skull, which was first attributed to *Homo guatengensis*. Lee Berger (2011) states there is little reason to leave *H, guatengensis* as valid, noting Stw 53 has a challenged attribution to *Homo* based on morphological and stratigraphic factor. He notes that MH1, the holotype of *Homo sediba* is is more similar to *Homo* than Stw 53 is, assigning the skull tentatively to *Australopithecus africanus*, or an *Australopithecus africanus*-like taxon related to *Homo sediba*.

## Paleoecology

In South Africa, australopithecines appear to have lived in a range of environments. Sterkfontein bears fossil wood from *Dichapetalum* cf. *mombuttense*, which, in the modern day, grows in the Congolian rainforests and is not present in the region anymore, and may suggest that this rainforest was once extended. Wildlife assemblages suggest bush savannas, open woodlands or grasslands. The shrub *Anastrabe intergerrima* was also discovered, which only grows on the moist South African coastline. This may indicate that at this time the Cradle of Humankind received more frequent rainfall, with gallery forests and the surrounding grasslands, Taung appears to have featured a wet, closed environment. They likely preferred cooler climates based on trends with australopiths and early *Homo*, since australopithecine remains are never found below 1000 meters at time of deposition. This would make (liek chimpanzees) an average diurnal temperature of 25 °Celsius (77 °Fahrenheit) and a nocturnal temperature of 10 or 5 °Celsius (50 or 41 °Fahrenheit). Studying *Paranthropus robustus*, Charles Kimberlin Brain (1983) hypothesizes that australopith remains accumulated in caves due to carnivore activity, where they dragged in corpses that would fossilize. However, he was unsure if the predators sought out australopithecines or if they lived deep in caves and ambushed them when they entered. Baboons from this region often shelter in sinkholes, especially on cold winter nights, though Brain thought that australopiths seasonally migrated out from Highveld to Bushveld, which was warmer, only living in caves in spring and autumn. *Australopithecus* from Sterkfontein Member 4 were likely accumulated by large cats with hunting hyenas and jackals probably aiding. Scratches, gouges and punctures on the Taung child are similar to crowned eagles, indicating it was killed by a bird of prey. Just before arrival of *Paranthropus robustus* and *Homo erectus* in the region, around 2.07 million years ago *Australopithecus* became extinct. It was possible South Africa acted as a refuge for *Australopithecus* until major climatic variability and volatility, or even competition with *Paranthropus* and *Homo*.

## Gallery

"Mrs. Ples"*Australopithecus* hand in the palm of The Box, Plymouth curator Jan Freedman.
## References

1. ↑ https://www.youtube.com/watch?v=49Mycdc9Z7o&ab\_channel=WitsUniversityOFFICIAL
2. ↑ https://www.pnas.org/doi/full/10.1073/pnas.2123516119
3. ↑ https://twitter.com/tylerstoneart/status/1374773538196967425 (thread)
4. ↑ https://royalsocietypublishing.org/doi/10.1098/rspb.2015.0943
5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 https://en.wikipedia.org/wiki/Australopithecus\_africanus
6. ↑ https://pubmed.ncbi.nlm.nih.gov/30777357/
7. ↑ https://cryptidarchives.fandom.com/wiki/Bigfoot
8. ↑ Broom (1936)
9. ↑ https://www.bradshawfoundation.com/origins/kenyanthropus\_platyops.php
10. ↑ Broom (1938)
11. ↑ Ferguson (1984)
12. ↑ https://www.newyorker.com/magazine/2016/06/27/lee-berger-digs-for-bones-and-glory
13. ↑ https://en.wikipedia.org/wiki/Little\_Foot
14. ↑ https://elifesciences.org/articles/64804
15. ↑ https://en.wikipedia.org/wiki/Mrs.\_Ples
16. ↑ https://en.wikipedia.org/wiki/STS\_14
17. ↑ https://en.wikipedia.org/wiki/STS\_71
18. ↑ https://en.wikipedia.org/wiki/StW\_505
19. ↑ https://en.wikipedia.org/wiki/Taung\_Child
20. ↑ https://en.wikipedia.org/wiki/Homo\_gautengensis