Australopithecines

Australopithecine is the informal adjective designating members of the taxonomic subfamily Australopithecinae, which with the Homininae constitute the family Hominidae. The Hominidae are humans, human ancestors and collateral species after the lineage branched from that leading to chimpanzees. Recently, paleontologists, influenced by evidence from genetics that apes and humans are more closely related than traditional taxonomy reflected, have pulled African apes into the Hominidae, with repercussions right down the taxonomic scale. Under the new scheme, gorillas are in the subfamily Gorillinae and chimpanzees and humans are in the Homininae. The Homininae is divided into two tribes, the Panini for chimpanzees and Hominini for our own lineage. Our tribe, the Hominini, is divided into two subtribes, the Australopithecina (less formally “australopiths”) and the Hominina, which contains only the genus Homo.

Except for specialists, the new taxonomy hardly affects the australopithecines. There is but a single difference: “australopithecines” are now referred to as “australopiths.” The old and new schemes are given in the table. Taxa in bold are discussed in this entry.

Australopiths as a group differ from chimpanzees and other apes in possessing more robust, less protruding (i.e., more orthognathic) faces. Australopith mandibles lack a “simian shelf” (a ridge of bone behind the chin that joins the two sides of the jaw) and are more robust. Australopiths have a shallower supratoral sulcus (groove behind the browridge) and a more caudally oriented nuchal plane (that is, the attachment of the neck muscles faces downward, reflecting a vertical spine). Australopith incisors are slightly smaller to much smaller than chimpanzees, molars and premolars are larger, dental enamel thicker to much thicker, and canine less projecting though still roughly triangular. Whereas ape lower first premolars have a sloping face that sharpens the back of the upper canine when the individual closes its mouth, australopith first premolars start out a little more molarlike in early species and have lost all evidence of this honing shape by 2.5 million years ago (Ma). Australopith canines typically wear from the tip, rather than along a knife-like rear edge, as in apes. The robusticity of the skull is thought by many to reflect an adaptation to chewing more fibrous foods. Fruits in open habitats are less succulent and more fibrous than the fruits chimpanzees eat, and australopiths likely also included fibrous underground storage organs in their diet.

Australopith skulls differ from those of Homo in having cranial capacities of less than 700 cc and usually < 600 cc. Australopiths have more prognathic (protruding) faces. All australopiths lack a true external [Page 312][Page 313]nose, but rather they quite resemble chimpanzees in this feature. Aside from cranial capacity, the skulls of earliest Homo, Homo habilis, as exemplified by ER 1470 and OH 7, are quite like those of South African australopiths.