australopithecine

n.
Any of several extinct humanlike primates of the genus Australopithecus, known chiefly from Pleistocene fossil remains found in southern and eastern Africa.

adj.
Of, relating to, or characteristic of these extinct humanlike primates.

[From New Latin Austrālopithēcus, genus name : Latin austrālis, southern; see austral¹ + pithēcus, ape (from Greek pithēkos).]

Any of the seven extinct species that belong to the family Hominidae (comprising humans and their closest relatives). These species are not attributable to the genus Homo, but belong to at least three genera that existed between about 4.4 million years ago (Ma) and 1.2 Ma during the Pliocene and early Pleistocene epochs. All seven species are known only from Africa. Although some workers regard all of them as belonging to one genus, Australopithecus, it is clear that a second genus, Ardipithecus, should be recognized for the earliest known hominid fossils, and that the three “robust” species belong to a third genus, Paranthropus.

The name australopithecine comes from the taxon Australopithecus (“southern ape”) africanus, which was coined by Raymond Dart for a fossil skull discovered in 1924 in Taung, South Africa (see illustration). The Taung skull had several distinctly hominid, or humanlike, features, but the claim that A. africanus was a human forebear was disputed by many of the leading paleoanthropologists of that time. The hominid status of A. africanus became widely accepted more than a decade later, largely because of work on Australopithecus fossils from Sterkfontein. Specimens of A. africanus are known also from the sites of Makapansgat and Gladysvale in southern Africa. Faunal comparison with radiometrically dated sites in eastern Africa indicates that this species existed between about 3.0 and 2.3 Ma. The name Paranthropus (“beside human”) was coined in 1938 when fossils from Kromdraai, South Africa, were attributed to the taxon P. robustus. Fossils of this species are also known from the nearby sites of Swartkrans and Drimolen. These bones are dated, also by faunal comparisons with radiometrically dated sites in eastern Africa, to between about 1.8 and 1.5 Ma.

Lateral view of the Taung skull of Australopithecus africanus, the type specimen of Australopithecus and the first early hominid specimen to be discovered in Africa. (Courtesy of F. E. Grine)

At least seven australopithecine species, belonging to at least three genera, can be recognized in the Pliocene and early Pleistocene of Africa: Ardipithecus ramidus (?5.0–4.4 Ma), Australopithecus anamensis (3.9–4.2 Ma), Australopithecus afarensis (?4.0–2.9 Ma), Australopithecus africanus (3.0–2.3 Ma), Paranthropus aethiopicus (2.8–2.3 Ma), Paranthropus boisei (2.3–1.2 Ma), and Paranthropus robustus (1.8–1.5 Ma). All are defined on the basis of craniodental morphology.

Paleoanthropologists disagree over the assignment of early hominid fossils to different genera and species. Such arguments over what is known as Alpha Taxonomy are to be expected, as different workers view the fossil record from different philosophical perspectives. Such differences also account for disagreements over the phylogenetic relationships of these species, including the issue of which (if any) is most closely related to the human genus, Homo. Every phylogenetic hypothesis that has been put forward since the 1950s has been either falsified outright or at least substantially altered by ongoing research and new discoveries.

At present, no scientifically rigorous phylogenetic analysis has been undertaken that incorporates all seven of the australopithecine species. The most comprehensive study of “australopithecine” evolutionary relationships to date does not include Ar. ramidus or A. anamensis. Nevertheless, it is evident from the descriptive account of Ar. ramidus that it very likely resembles the stem hominid taxon in its morphology. Australopithecus anamensis shares some evolved (derived) traits with later species such as A. afarensis, but retains some primitive features that are displayed also by Ar. ramidus. Thus, A. anamensis most likely evolved from a species that was at least morphologically similar to Ar. ramidus in some respects. For the moment, Ar. ramidus represents the best candidate for the ancestor of A. anamensis. Australopithecus anamensis, in turn, possesses some unique features that make it unlikely to be the immediate ancestor of A. afarensis, but it is probable that A. afarensis evolved from a species that had a strong morphological resemblance to A. anamensis.

Australopithecus afarensis likely gave rise to a lineage that provided the ancestry of both A. africanus and another lineage that included the common ancestor of the genera Paranthropus and Homo. Although A. africanus shares a number of derived morphological characters with species that are part of the Paranthropus and Homo lineage, it is not considered to be directly ancestral to that line because it exhibits derived morphology in several characters that are more primitive in both A. afarensis and P. aethiopicus. It is perhaps more likely that the derived traits which A. africanus shares with some species of Paranthropus and Homo were evolved in parallel. Other workers, however, have argued that A. africanus constitutes a reasonable morphotype for the last common ancestor of the lineage that leads to Homo and Paranthropus. In this case, the primitive features displayed by P. aethiopicus would represent evolutionary reversals. At present, then, it is safest to conclude that the phyletic position of A. africanus remains ambiguous.

Paranthropus aethiopicus is considered to be a likely candidate for the ancestry of both P. boisei and P. robustus. The reason is that P. aethiopicus shares a number of primitive features with A. afarensis, but at the same time it shares a host of derived features with the later species of Paranthropus, namely P. robustus and P. boisei.

The lineage leading to Paranthropus shares a number of morphological features with that leading to Homo. For example, all species of Homo and Paranthropus share a coronally oriented petrous temporal bone, a foramen magnum that is roughly horizontal in disposition, and a vertically oriented mandibular symphysis. Thus, it is most parsimonious to assume that these two lineages shared a common ancestor at some time prior to 2.8 Ma.

The apparent increase in cranial capacity that is shown by some species of Paranthropus (P. robustus and P. boisei) would appear to parallel the increase in brain size that characterized the evolutionary history of the lineage that led to Homo sapiens. Tools made of stone or bone are not known to be associated with Ardipithecus or the three species of Australopithecus. Stone tools are known from sites that contain P. boisei fossils, and both bone and stone tools are known from sites that preserve P. robustus remains. However, early members of the genus Homo are known also from these same localities. Thus, it is difficult to determine whether Paranthropus species may have been responsible for some of the late Pliocene and early Pleistocene archeological record. Indeed, it has been argued that the later species of Paranthropus may have been driven to extinction through competition with early Homo, because the latter possessed a distinct ecological advantage through the utilization of lithic technology in the procurement of food. While the evidence for this is not compelling, it is possible that ecological interactions between Paranthropus and early members of Homo may have influenced the evolutionary course of the human genus. See also Apes; Fossil humans.

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The noun has one meaning:

Meaning #1: any of several extinct humanlike small-brained bipedal primates of the genus Australopithecus; from 1 to 4 million years ago

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The adjective australopithecine has one meaning:

Meaning #1: of or belonging to the hominid genus Australopithecus
  Pertains to noun: genus Australopithecus (meaning #1)

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