primate adaptations

Social Organization Adaptation

anatomy (teeth, body size, and testes size) reflects social organization and mating systems in primates

polygynous

one male, multi female

female coalitionary competition

levels of dimorphism influenced by female social strategies, female coalitions reduce advantages of large male canines

canine size (from biggest to smallest)

single male group, multimale group, polyandrous/monogamous group

body size dimorphism (from biggest to smallest)

single male group, multimale group, polyandrous/monogamous group

relative testes size (from biggest to smallest)

multimale group, polyandrous/monogamous group, single male group,

body size

places opportunities & restrictions on a species’ ecological options

the square cube law

as an animal gets large, its volume & weight increases much faster than its surface area

problems caused by square cube law

supporting body weight, dissipating heat, digestion, and brain function

what evolutionary tricks have primates developed to handle these size constraints?

evolving different physical proportions, postural & behavioral changes that reduce stress on bones (small primates have a flexed limb gait & large primates have an extended limb gait)

arboreal quadrupeds skeletal adaptations

narrow thorax, long tail for balance, laterally placed scapula

arboreal quadrupeds limb adaptations

limbs of roughly equal length, grasping hands & feet with opposable big toe

terrestrial quadrupeds skeletal adaptations

narrow thorax, short/reduced tail, restricted shoulder joint mobility

terrestrial quadrupeds limb adaptations

longer forelimbs than hindlimbs, robust joints

leapers skeletal adaptations

elongated ankle bones (tarsals), upright trunk posture

leapers limb adaptations

very long & powerful hindlimbs, short forelimbs

suspension (brachiators) skeletal adaptations

dorsally placed scapula, highly mobile shoulder joint, short stiff lumbar spine, broad thorax

suspension (brachiators) limb adaptation

hook-like hands/long curved fingers, very long forelimbs relative to hindlimbs, reduced thumbs

frugivory teeth adaptations

low & rounded molar cusps (grinding pulp) and broad incisors (to crack fruit)

frugivory digestion adaptations

long & small intestine (rapid absorption of simple sugars)

folivory teeth adaptations

well-developed molar shearing crests (slice leaves) and small incisors

folivory digestion adaptations

large caecum, complex stomach, enlarged large intestine

insectivores/faunivores teeth adaptations

sharp pointed cusps on all teeth (piercing insect exoskeletons)

insectivores/faunivores digestion adaptation

short, simple gut

gum eaters teeth adaptations

stout incisors (bark gouging)

gum eaters digestion adaptations

long caecum

gum eaters digit adaptations

claws on digits (tree clinging while feeding)

brain size hypotheses

Social Brain Hypothesis & Dietary Hypothesis

Dietary Hypothesis

large brains evolved to solve ecological problems (harder/complex diets like patchy, seasonal, extractive = bigger brains)

frugivore species

chimps, baboons, spider monkeys (ateles)

folivore species

howler monkeys (alouatta), colobus monkeys, macaques

insectivore species

tarsiers

gum eaters

fork marked lemur

polygynous species

baboons, gorillas

monogamous species

gibbons (hylobates)