Which group of early primates is characterized by having fossils that account for a significant number of species from the early Eocene?

The correct answer is the group characterized by having fossils that account for a significant number of species from the early Eocene: Euprimates. During the early Eocene epoch, approximately 56 to 34 million years ago, Euprimates emerged as the first true primates, exhibiting features indicative of modern primate morphology.

Euprimates are significant because they include recognizable ancestors of both strepsirrhines (like lemurs and lorises) and haplorhines (like tarsiers and anthropoids). The diverse fossil record from this period shows a variety of species that illustrate the rapid diversification and adaptation of primates in response to changing environments.

The other groups mentioned, such as Plesiadapiforms, although important early primates, belong to a separate group that predates the Eocene and does not represent true primates as understood today. Anthropoids are more advanced primates and came later in the evolutionary timeline, while "primate ancestors" is a broad term that does not specifically denote a defined group like Euprimates. Hence, Euprimates are distinct for their abundance and diversity in the early Eocene fossil record.