Nature has a short blurb about Suminia getmanovi, a 260 million year old fossil that is the earliest evidence of an arboreal vertebrate. The blurb doesn’t tell too much, although it does have a very sweet picture. Apparently, evidence for arboreal behavior in this fossil includes elongated limbs, [something unelaborated upon about] its digits, and a long tail. It may have had a prehensile tail (like the Neotropical Ateline primates, including howler monkeys and spider monkeys), and possibly an opposable thumb (like in all true primates).
Given the fossil’s great antiquity and its potentially primate-like anatomy, one may ask, ‘Is this the common ancestor of all primates–are primates as ancient as the Permian Therapsids (a bad-ass group of ancient animals, also known as “mammal-like reptiles”)?’ Of course not. Rather, it is a great lesson in evolution: if there’s a niche to be filled, something will fill it, which means convergent evolution has probably been pretty common in the history of life. Flying evolved independently in dinosaurs, birds and mammals. Arboreal predation evolved in parallel in the marsupial Caluromys and (possibly) the first true Primates–there are several examples of convergent evolution in marsupials (Metatherians) and Eutherian (like us!) mammals. In fact, gliding evolved independently in the Jurassic mammal Volaticotherium, the (modern) marsupial sugar gliders (Petaurus), and the (modern) Eutherian colugos. Oh, and then there’s the ‘single-lens camera eye’ that evolved independently in cephalopods and vertebrates.
So, where there are similar niches to be filled, there’s a good chance that different animals will independently evolve similar adaptations to fill these niches. To quote one of D. Futuyma’s Principles of Evolution: homoplasy is common in evolution.