Australopithecus first appeared on Earth 5 million years ago, which is right about here on the timeline. They survived until 1 million years ago, and overlapped with Homo Habilis and Homo Erectus. The most famous Australopithecus is Lucy. She was found by archaeologist Don Johanson. Australopithecus had brains the size of an orange and were the earliest human ancestor. Their features included long arms, human-like hands and feet and large heads. Australopithecus was also short compared to humans today. They were 3 to 4 feet tall on average. They were also bipeds. Being bipeds meant that Australopithecus could walk on two feet. They used tools too, but they did not make them. For example, a stick could be used to dig. Australopithecus' existance overlapped with that of Homo Habilis. The meaning of the name "Australopithecus" is Southern Ape. From the photo, you can infer that they did not really have a forehead and that their skull is small, which means that their brain did not have a lot of room. From the video, you can tell that Lucy was a very important discovery.
This information came from the Becoming Human Video and the Early Hominids website.