Australopithecine

Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally Australopithecus (cladistically including the genera Homo, Paranthropus,[3] and Kenyanthropus), and it typically includes the earlier Ardipithecus, Orrorin, Sahelanthropus, and Graecopithecus. All these related species are now sometimes collectively termed australopiths or homininians.[4][5] They are the extinct, close relatives of humans and, with the extant genus Homo, comprise the human clade. Members of the human clade, i.e. the Hominini after the split from the chimpanzees, are now called Hominina[6] (see Hominidae; terms "hominids" and hominins).

Australopiths
Temporal range: Pliocene–Present, 5.6 – 0 Mya (Range includes humans (Homo))
Australopithecus sediba
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Subtribe: Australopithecina
Gregory & Hellman, 1939
Type species
†Australopithecus africanus
Dart, 1925
Genera
Synonyms

Hominina Gray 1825[2]

While none of the groups normally directly assigned to this group survived, the australopiths 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 sister of a late Australopithecus species such as A. africanus and/or A. sediba.

The term australopithecine came from a former classification as members of a distinct subfamily, the Australopithecinae.[7] Members of Australopithecus are sometimes referred to as the "gracile australopiths", while Paranthropus are called the "robust australopiths".[8][9]

The australopiths occurred in the Plio-Pleistocene era and were bipedal, and they were dentally similar to humans, but with a brain size not much larger than that of modern apes, with lesser encephalization than in the genus Homo.[10] Humans (genus Homo) may have descended from australopith ancestors and the genera Ardipithecus, Orrorin, Sahelanthropus, and Graecopithecus are the possible ancestors of the australopiths.[9]

Classification

Classification of subtribe Australopithecina according to Briggs & Crowther 2008, p. 124.

Phylogeny

Phylogeny of Hominina/Australopithecina according to Dembo et al. (2016).[11]

 

Sahelanthropus tchadensis

 
 
 

Ardipithecus

 
 
 

Australopithecus anamensis

 
 
 
 

Australopithecus afarensis

 
 

Australopithecus garhi

 
 
 
 

Kenyanthropus platyops

 
 
 
 

Australopithecus africanus

 
 
 

Paranthropus aethiopicus

 
 
 

Paranthropus robustus

 
 

Paranthropus boisei

 
 
 
 
 

Homo (including "Australopithecus" sediba)

 
 
 
 
 
 

Physical characteristics

The post-cranial remains of australopiths show they were adapted to bipedal locomotion, but did not walk identically to humans. They have a high brachial index (forearm/upper arm ratio) when compared to other hominins, and they exhibit greater sexual dimorphism than members of Homo or Pan but less so than Gorilla or Pongo. It is thought that they averaged heights of 1.2–1.5 metres (3.9–4.9 ft) and weighed between 30 and 55 kilograms (66 and 121 lb). The brain size may have been 350 cc to 600 cc. The postcanines (the teeth behind the canines) were relatively large, and had more enamel compared to contemporary apes and humans, whereas the incisors and canines were relatively small, and there was little difference between the males' and females' canines compared to modern apes.[9]

Relation to Homo

Most scientists maintain that the genus Homo emerged in Africa within the Australopiths around two million years ago. However, there is no consensus on within which species:

"Determining which species of australopith(if any) is ancestral to the genus Homo is a question that is a top priority for many paleoanthropologists, but one that will likely elude any conclusive answers for years to come. Nearly every possible species has been suggested as a likely candidate, but none are overwhelmingly convincing. Presently, it appears that A. garhi has the potential to occupy this coveted place in paleoanthropology, but the lack of fossil evidence is a serious problem. Another problem presents itself in the fact that it has been very difficult to assess which hominid [now "hominin"] represents the first member of the genus Homo. Without knowing this, it is not possible to determine which species of australopith may have been ancestral to Homo."[9]

Asian australopiths
See also: Meganthropus

A minority held viewpoint among palaeoanthropologists is that australopiths moved outside Africa. A notable proponent of this theory is Jens Lorenz Franzen, formerly Head of Paleoanthropology at the Research Institute Senckenberg. Franzen argues that robust australopiths had reached not only Indonesia, as Meganthropus, but also China:

"In this way we arrive at the conclusion that the recognition of australopithecines in Asia would not confuse but could help to clarify the early evolution of hominids ["hominins"] on that continent. This concept would explain the scanty remains from Java and China as relic of an Asian offshoot of an early radiation of Australopithecus, which was followed much later by an [African] immigration of Homo erectus, and finally became extinct after a period of coexistence."[12]

In 1957, an Early Pleistocene Chinese fossil tooth of unknown province was described as resembling P. robustus. Three fossilized molars from Jianshi, China (Longgudong Cave) were later identified as belonging to an Australopithecus species (Gao, 1975). However further examination questioned this interpretation; Zhang (1984) argued the Jianshi teeth and unidentified tooth belong to H. erectus. Liu et al. (2010) also dispute the Jianshi-australopithecine link and argue the Jianshi molars fall within the range of Homo erectus:

"No marked difference in dental crown shape is shown between the Jianshi hominin and other Chinese Homo erectus, and there is also no evidence in support of the Jianshi hominin's closeness to Australopithecus."

But, Wolpoff (1999) notes that in China "persistent claims of australopithecine or australopithecine-like remains continue".

See also

Notes
  1. Stanford 2012.
  2. Gray, J. E. (1825). "An outline of an attempt at the disposition of Mammalia into Tribes and Families, with a list of genera apparently appertaining to each Tribe". Annals of Philosophy, new series. 10: 337–334.
  3. Wood 2010.
  4. Wood & Richmond 2000.
  5. Briggs & Crowther 2008, p. 124.
  6. "GEOL 204 The Fossil Record: The Scatterlings of Africa: the Origins of Humanity". www.geol.umd.edu. Retrieved 24 December 2016.
  7. Kottak 2004.
  8. Mai, Owl & Kersting 2005.
  9. Szpak, P. (2007). "Evolution of the Australopithecines". Tree of Life.
  10. Mai, Owl & Kersting 2005, p. 45.
  11. Dembo, Mana; Radovčić, Davorka; Garvin, Heather M.; Laird, Myra F.; Schroeder, Lauren; Scott, Jill E.; Brophy, Juliet; Ackermann, Rebecca R.; Musiba, Chares M.; de Ruiter, Darryl J.; Mooers, Arne Ø. (1 August 2016). "The evolutionary relationships and age of Homo naledi: An assessment using dated Bayesian phylogenetic methods". Journal of Human Evolution. 97: 17–26. doi:10.1016/j.jhevol.2016.04.008. hdl:2164/8796. ISSN 0047-2484.
  12. Franzen 1985.

References
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