The Australopithecus is a genus corresponding to a particular type of hominin that developed certain locomotion patterns and had a derived dentition when compared to chimpanzees and earlier hominins. Several taxa fall within such a characterization. Strait el al. (1997) have pointed out that the taxon Australopithecus, conventionally defined as the set of all hominins prior to Homo— except Ardipithecus—that were known at the time, constitutes a paraphyletic group. That is, Australopithecus was at that time a hodgepodge in which to place all early hominins that did not fit elsewhere. Strait and colleagues (1997) took into account the following taxa in their study: A. afarensis, A. africamis, A. aethiopicits, A. robustus, and A. boisei. Table 4.1 includes other species that were not known at the time, such as A. anamensis and Australopithecus garhi, but the issues raised by Strait et al. do not change by this inclusion. The consequence of defining the genus Australopithecus in such a broad way is that specimens that cannot be grouped in a single evolutionary lineage are ultimately included together.
One way to resolve the problem, so that genera can be defined that constitute true lineages, is to separate "robust" australopitheories from the other taxa. The distinction between robust and gracile hominins was set up as a consequence of the discovery of fossils that exhibited very different features, but were found in close South African sites during the first half of the twentieth century. It is necessary to introduce a historical note here. The cranial traits of the Taung specimen, used by Raymond Dart to define, in 1925, the genus Australopithecus (Dart, 1925) and those found later at Sterkfontein and Makapansgat did not appear massive, lacking a sagittal crest. Robert Broom (1938) later discovered much more robust specimens at Kromdraai, similar to those found later at Swartkrans. Although Broom suggested the genus and species Paranthropus robustus for them, many authors just distinguished between gracile A. africamis, and robust Australopithecus robust us. However, later findings at Olduvai (Tanzania) required the revision of this relative concept of robusti-city and gracility. Early Homo from Olduvai was more gracile than A. africamis. Moreover, gracile Australopithecus are much older than the robust specimens and than Olduvai Homo habilis. These two last types of hominin are approximately the same age. So, the distinction between gracile and robust forms should be used to refer to two lineages, one specialized in the intake of hard vegetables, and the other a carnivorous lineage.