Final answer:
Australopithecines such as Australopithecus afarensis, distinguishable from apes by relatively smaller canines, also exhibited bipedality and larger brains compared to apes, with many human-like traits that mark them as important ancestors in human evolution.
Step-by-step explanation:
One feature that distinguished australopithecines from apes was relatively smaller canines.
Australopithecus species, such as Australopithecus afarensis, which lived between 3.9 and 2.9 million years ago, had smaller canines and molars compared to apes. This reduction in tooth size, specifically the size of the canines, is a notable difference between australopithecines and apes. Australopithecines also exhibited other key humanlike traits, including bipedalism (walking on two limbs), larger brains relative to their body size compared to apes, albeit not as large as modern humans, and a fully upright posture. While the increase in brain size in later hominins like Homo habilis was significant, with brain volumes around 800 cubic centimeters, australopithecines like A. afarensis had brain sizes of about 380 to 450 cubic centimeters, which is roughly the size of a modern chimpanzee's brain but larger than that of earlier primates. Thus, distinguishing australopithecines from apes include their smaller canines, bipedality, and slightly larger brains.