Final answer:
During the Miocene period, early apes such as Proconsul africanus and Sivapithecus existed, with the former being one of the earliest and demonstrating quadrupedal movement, and the latter showing similarities to orangutans. Additionally, there are Miocene fossils like Samburupithecus and Oreopithecids, which are connected to modern African apes and humans.
Step-by-step explanation:
During the Miocene period, several ancestors of modern apes roamed the Earth. One of the earliest Miocene apes, Proconsul africanus, lived approximately 23 to 14 million years ago. These apes lacked the long, curved digits of their modern descendants, indicating that although they could hang from branches, they more commonly moved on all fours. Proconsul was also tailless, which is a defining characteristic of apes rather than monkeys. Furthermore, their dental pattern followed the 2.1.2.3 formula, which is consistent with all Old-World monkeys and apes, including humans.
Sivapithecus is another significant Miocene ape, commonly found in Asia, and noted for their thick dental enamel. This suggests a diet of hard foods. The skull morphology of Sivapithecus has a striking similarity to that of the modern orangutan, particularly in the structure of nasal openings and eye sockets.
The end of the Miocene also saw large apes like Samburupithecus, akin to modern African apes, and Oreopithecids, which had facial features connecting it to both African apes and humans. However, the ancestors of the modern African great apes and their lineage still remain largely unclear.