To prove that Au. anamensis branched from an earlier, as-yet-unknown population would require evidence that the Australopithecus species lived at the same time as Ar. ramidus, the Berkeley scientist notes. No such evidence exists.
That's a rather large leap of logic.
"That's a rather large leap of logic."
It's clearly their working hypothesis and it is based on the little information they have. Why is it a leap of logic?