Fossils effectively do. We have a great idea of when birds came about due to the fossil record, same with whales.
unless you think it’s a coincidence that we have a lot of bird-like-dinosaurs that increasingly lose/gain characteristics similar to birds.
Im also not sure what you mean with Australopithecus? Do you mean it’s physical appearance? Because it should resemble a mix between chimps and humans. Orangutans are the out-group for great apes, every other great ape is more closely related to one another than they are to organutans
Most paleontologists avoid “primitive” these days and use basal, as to not confuse readers. It’s more saying something is further down the evolutionary tree, as opposed to saying it’s lesser to current animals.