In 1984 American paleoanthropologist Walter Ferguson decried Australopithecus afarensis as a species. At the time, the known fossils of Au. afarensis came from sites in Ethiopia and Tanzania.
The considerable variation in the bones of this combined collection were generally thought due to size differences between male and female members of the species. But Ferguson believed the bones belonged to more than 1 species. Based on the size and shape of molars, Ferguson concluded that some of the larger jaws matched those of Au. africanus, while the littler jaws had smaller, narrower Homo-like teeth. The 3-million-year-old fossils were too old to fit with any known Homo, so Ferguson named a new species: H. antiquus.
Ferguson’s species splitting had a larger implication: if Australopithecus and Homo lived side by side for hundreds of thousands of years, it was unlikely that australopithecines were the direct ancestors of Homo.
However merited, Ferguson’s work did not convince to consensus. Au. afarensis is still around, while few have ever heard of H. antiquus.