Final answer:
The genus ancestral to platyrrhines in South America during the Oligocene epoch, with dental remains suggesting frugivory, is likely the Propliopithecoidea. They had low, rounded cusps on their molars, indicative of a frugivorous diet. Although the first definitive platyrrhine fossils were found in Africa, subsequent evolution occurred after they arrived in South America.
Step-by-step explanation:
South American Genus from the Oligocene
The question refers to the early ancestors of platyrrhines, the New World monkeys from the Oligocene epoch. The Oligocene epoch spans from approximately 34 million years ago (MYA) to about 22 MYA. During this time, a significant genus ancestral to platyrrhines is believed to be the Propliopithecoidea, which are early haplorrhine fossils found in the Fayum region of Africa, suggesting African roots for these New World monkeys. The teeth of these primates indicate that their diet was likely frugivorous, as they had low, rounded cusps on their molars, suitable for eating fruit.
It's worth noting that even though the first definitive platyrrhine fossils were found in Africa, significant evolutionary developments likely took place after their ancestors reached South America. The presence of a third premolar and a dental formula of 2.1.2.3 is significant in understanding the evolution of New World monkeys. The early primates' dental characteristics suggest a close relationship with frugivorous diets.
Analogous to the robust and gracile australopithecines, we can infer that the development of dental morphology is closely tied to dietary habits. For instance, Paranthropus, a robust australopithecine genus, had significantly larger teeth adapted for a tough, fibrous diet, unlike the preceding australopithecines which had smaller teeth suggesting a softer diet. Similarly, the dental evidence from early platyrrhines suggests fruit consumption played a critical role in their diet based on tooth morphology.