Final answer:
Primates, including humans, exhibit post-cranial features like a rotating shoulder joint, widely separated toes and thumbs, stereoscopic vision, and large brains, which are adaptions from their tree-dwelling ancestors. Humans specifically have evolved for bipedalism, with shortened arms relative to their legs, increased dexterity, and enlarged brains, particularly in the frontal lobes. Other characteristics involve flattened nails and typically a single offspring per pregnancy.
Step-by-step explanation:
Physical Features of Primates: Post Cranial
The physical features of primates post-cranially include distinctive traits that support their arboreal heritage and facilitate versatile movement both in trees and on the ground. These traits are:
- A rotating shoulder joint, allowing a wide range of arm motion, important for brachiation (swinging through trees) or other forms of locomotion.
- A big toe widely separated from other toes and an opposable thumb (in non-human primates), aiding grip and manipulation of objects.
- Stereoscopic vision for depth perception, crucial in navigating arboreal environments.
- Brains larger than those of most other mammals, particularly in the cerebrum, facilitating complex behaviors and high intelligence.
- Flattened nails instead of claws.
- Usually producing only one offspring per pregnancy, allowing for more intense parental care.
- A tendency to hold the body upright, seen in the semi-erect or erect posture of primates.
Additional post-cranial characteristics specific to Homo sapiens include:
- A fully erect posture leading to bipedalism, a mode of locomotion unique to humans among extant primates.
- Arms shortened relative to legs, enhancing bipedal efficiency.
- Increased dexterity in the hands.
- An increase in brain size, especially in the frontal lobes.
- A reduction in bone mass in the skull and face.
The primate shoulder girdle featuring a collar bone (clavicle) supports versatile limb motion, and curved fingers suggest adaptations for climbing and swinging, indicators of a primitive shoulder position suitable for an arboreal lifestyle.