Introduction:
The extinct human ancestor who ate only fruits and hunted with stone weapons is Australopithecus.

Explanation:
Australopithecus is an extinct genus of hominins that lived between 4.2 and 1.9 million years ago in Africa. They were early human-like creatures that had both ape-like and human-like characteristics. One of the key aspects of their diet and lifestyle was their reliance on fruits and the use of stone tools for hunting.

Diet:
Australopithecus primarily consumed fruits as their main source of food. Their teeth and jaws were adapted for chewing and processing fruits. The dental morphology of Australopithecus, with thick enamel and large molars, indicates that they had a specialized diet of tough, fibrous plant materials such as fruits, nuts, and seeds. This suggests that they were primarily frugivorous, meaning they relied heavily on fruits for their nutrition.

Stone Tools:
Australopithecus is also known for its use of stone tools. Although they were not as advanced as later hominin species like Homo erectus, they used simple stone tools for various purposes, including hunting. These tools were primarily used for smashing bones and accessing the marrow inside, indicating that they were involved in scavenging or hunting activities.

Evolutionary Significance:
Australopithecus is considered an important transitional species in human evolution. They displayed a combination of primitive and advanced traits, making them a crucial link between our ape-like ancestors and early human species. Their adaptation to a diet consisting of fruits and the use of stone tools for hunting marked a significant step in the development of human ancestors.

Conclusion:
In summary, Australopithecus is the extinct human ancestor that ate only fruits and hunted with stone weapons. Their frugivorous diet and the use of stone tools for hunting and scavenging played a crucial role in their evolution and paved the way for the emergence of later human species.