What is the main reason that australopithecus garhi has been proposed as an ancestor for homo?

Fossils of Australopithecus gardhi are associated with some of the oldest known stone tools, along with animal bones that weer cut and broken open with stone tools. It is possible that, then this species was among the first to make the transition to stone toolmaking and to eating meat and bone marrow from large animals. Scientists claim that the large molar teeth show that Australopithecus gardhi is related to Paranthropus aethiopicus; however the combination of features of the face, brain case and teeeth are unlike Paranthropus. Scientists find thinks that Australopithecus represent an ancestor of the genus Homo.