Various smaller-, bipedal hominins.
These include members of genus genus Australopithecus as well as members of genus .
The australopiths lived from at most about 4.5 to 1.5 million years ago. Together they are considered to be a paraphyletic grouping because of the omission of their descendant clade, genus Homo.
Video (Attempts at animating Australopithicus with some discussion of evidence for its bipedalism)
Video (Comparing the skull of Australopithicus afarensis to that of Homo sapiens)
Video (A song, very nicely done, though keep in mind that the robust species are now assigned to genus Paranthropus)