Before "P. boisei" was described (and "P. robustus" was the only member of "Paranthropus"), Broom and Robinson continued arguing that "P. robustus" and "A. africanus" (the then only known australopithecines) were two distinct lineages. However, remains were not firmly dated, and it was debated if there were indeed multiple hominin lineages or if there was only 1 leading to humans. In 1975, the "P. boisei" skull KNM-ER 406 was demonstrated to have been contemporaneous with the "H. ergaster" skull KNM ER 3733, which is generally taken to show that "Paranthropus" was a sister taxon to "Homo", both developing from some "Australopithecus" species, which at the time only included "A. africanus". In 1979, a year after describing "A. afarensis" from East Africa, anthropologists Donald Johanson and Tim D. White suggested that "A. afarensis" was instead the last common ancestor between "Homo" and "Paranthropus", and "A. africanus" was the earliest member of the "Paranthropus" lineage or at least was ancestral to "P. robustus", because "A. africanus" inhabited South Africa before "P. robustus", and "A. afarensis" was at the time the oldest known hominin species at roughly 3.5 million years old. Now, the earliest known South African australopithecine ("Little Foot") dates to 3.67 million years ago, contemporaneous with "A. afarensis".