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e Flattened Nails O O O O Having claws is the ancestral condition among mammals The earliest mammals had claws Early primates evolved nails which replaced claws Only tamarins and small monkeys have claws, but claws re-evolved from monkey ancestors who had flattened nails Represents a major shift in the function of the limbs in the primate lineage e forward -facing eyes O Most primates, eyes are shifted around from the size of the head to the front In all monkeys and apes and us humans are eyes are very close together Among apes and humans, our eyes are separated about the width of an eye Having eyes close together provides and have a major advantage Animals with eyes on the sides of their head have 360 degree view Horses can see in every direction without having to move their head but back of head is blind spot Horses and deers have poor depth perception since eyes are on side of head Dog and cat family have more forward facing eyes and improved depth perception Stereoscopic vision: gives better depth perception, the left and right eyes take visual information independently of each other but with this vision, the left eye and right eye overlap, so brain gets two independent sources of spatial information on the physical world right in front of it Compares and collects data and allows brain to refine data and determine where these objects sit in the 3 dimension world, having eyes close together does limit our peripheral vision Why? Form hypotheses to show the advantages of these traits e Arboreal Hypothesis (Wood-Jones and Elliot-Smith,1920) m Argued that these 3 traits are ones that will logically develop for adaptation for living full time in the trees and moving rapidly through the branches m Allow species to safely leaping from branch to branch and grasping fruit or insects with great precision e Visual Predation Hypothesis(Cartmill 1970) o Noted that squirrels are very well adapted to living in trees but lack these 3 primate traits m Have claws, eyes on side of head, fingers and toes are prehensile m He argued that rather than being for arboil living, forward facing eyes and