Final answer:
Australopithecus garhi is considered a potential direct ancestor to later hominins due to its transitional characteristics and evidence suggesting its use of stone tools. This is supported by cut marks on ruminant bones found in association with A. garhi fossils, indicating butchering with tools that predate Homo habilis's tool use.
Step-by-step explanation:
Australopithecus garhi is thought to be a direct ancestor to later hominins primarily because it exhibits characteristics that are transitional between the earlier australopithecines and the later species of the genus Homo. Specifically, A. garhi has a cranial capacity slightly greater than A. afarensis at 450 cubic centimeters and large incisors whose function is not fully understood. However, the most compelling evidence for its place in human evolution is the association of A. garhi fossils with stone tools. Fossil bones of ruminants with cut marks indicative of butchering have been found alongside A. garhi remains, suggesting that this species utilized stone tools, predating the known tool use of Homo habilis.
While there is still some debate about whether A. garhi directly made these tools, the use of tools is supported by the cut marks on bones found in close proximity to their fossils. This evidence challenges the previously held belief that H. habilis was the earliest tool user. Instead, it indicates that tool use arose earlier in hominin evolution, with A. garhi as a possible candidate for the initiation of this behavior.