23 million years ago: the origin of apes.
Fossilization of an organism happens when its organic remains are buried under sediment or volcanic ash. There are very few ape fossils because apes arose and evolved in regions where fossilization does not occur. They inhabit warm, tropical rainforests, where organic material decomposes rapidly and does not preserve. However, thanks to modern molecular biology, we know apes originated around 23 million years ago.
Apes differ from other primates for not having a tail. Currently, the only surviving ape species are gibbons, orangutans, gorillas, chimpanzees, bonobos and humans. The oldest known remains of an ape are those of Morotopithecus bishopi, dated 20.6 million years ago. They were found on Mount Moroto, an extinct volcano in Uganda.
7 million years ago, the region of Tuscany, in Italy, was a series of islands in the Mediterranean. Another ape called Oreopithecus bambolii flourished in this region. It probably survived after migrating from Africa and lived totally isolated for 3 million years. The most interesting thing about this ape is that its fossils show it had developed bipedalism, independently from our hominid ancestors.