Final answer:
The prosimians, which include species like lemurs and tarsiers, have retained the most ancestral traits of all primate groups. They exhibit physical characteristics likely present in the common ancestors of all primates due to their earlier evolutionary divergence.
Step-by-step explanation:
The primate group that retained the most ancestral traits is the prosimians. This group includes species like lemurs, aye-ayes, and tarsiers. Prosimians tend to be smaller, nocturnal, and have relatively smaller brains compared to anthropoids such as monkeys, apes, and humans. Prosimians represent an earlier branch of the primate evolutionary tree and thus have retained more of the physical characteristics that were likely present in the common ancestors of all primates. These ancestral traits include adaptations for climbing, such as grasping extremities which may have developed in response to the need for fine tactile and visual discrimination to feed on angiosperms, evidencing a close relationship in the evolutionary history between flowering plants and primate origins.
Primates share key features such as pentadactyl limbs (five-fingered hands), various types of teeth, stereoscopic vision, and an opposable thumb. Despite the evolution of different primate species, these features can still be seen throughout the primate order, linking them to their arboreal heritage and omnivorous diet which was deeply influenced by the angiosperm theory. As humans, we share many of these traits and genetic material with primates, which provides evidence of our common ancestry, but it is the prosimians who exhibit the closest connection to the earliest primate origins.