The term Australopithecine ('australos' for short) refers to any species in the related genera Australopithecus or Paranthropus. These genera occurred in the Pliocene–Pleistocene era, and were bipedal. The arrangement of their teeth, especially the dental arcade, was similar to humans. They did not have the large canine teeth characteristic of present-day apes.
They had a brain size not much larger than modern apes, lacking the large brain of the genus Homo. They were mainly bipedal, but probably capable of climbing and living at least partly in trees. Their arms were longer in proportion to their bodies, and this also suggests their inherited capacity to move above the ground. The efficiency of their walking is difficult to estimate, but they were not so well adapted to bipedalism as humans. The males were much larger than the females, which suggests a family arrangement with a dominant male and several females, as with modern apes. Nothing is known for certain about their use of tools.
When used alone, the term refers to both genera together. Australopithecus is sometimes referred to as the "gracile (slender) australopithecines", while Paranthropus are also called the "robust australopithecines".
- Kenyanthropus (3.5 to 3.2) mya is either a separate genus of australos, or a species of Australopithecus.
- Ardipithecus (5.6 and 4.4) mya, is a Miocene hominin. It had a grasping big toe, and therefore could live in trees as well as on the ground. The term "facultative biped" is used.
- Sahelanthropus, also a Miocene hominin, lived about seven million years ago (mya). The relationships of this species to the australos is unclear.
- Orrorin, at 6.1 to 5.7 mya is known from 20 pieces of bone, and its relationships are unclear. Orrorin is both earlier, by almost 3 million years, and more similar to modern humans than is A. afarensis. The main similarity is that the Orrorin femur is morphologically closer to that of H. sapiens than is Lucy's; there is, however, some debate over this point.
A likely ancestor of the australopithecines is the Ardipithecus genus, which lived in East Africa. The genus Homo (humans), appears about 2.4 million years ago with Homo habilis. Australos moved into mixed savannah/woodland habitats as the climate cooled in the later Miocene. This explains their adaptations to walking or walking plus climbing. It also explains the changes to their diet and teeth, though not in detail. The great increase in brain size of modern man began with the genus Homo: it did not start with the australos.
The australopithecines according to Briggs & Crowther.
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