Primate Evolution & Classification: Key Fossils, Traits, and Hypotheses

Paleocene (66-56 mya)

First primate-like mammals (plesiadapiforms) appear; warm tropical climate.

Eocene (56-34 mya)

First true primates (euprimates); early strepsirrhines and haplorhines evolve; tropical forests widespread.

Oligocene (34-23 mya)

Anthropoids diversify; early catarrhines like Aegyptopithecus appear; climate cools and dries.

Miocene (23-5.3 mya)

"Age of Apes"; hominoids diversify; early hominins appear near end.

Pliocene (5.3-2.6 mya)

Australopithecines evolve in Africa; bipedalism well established.

Pleistocene (2.6 mya-11,700 years ago)

Genus Homo expands; Homo erectus, Neanderthals, and modern humans appear; Ice Ages; stone tools develop.

Holocene (11,700 years ago-present)

Modern humans dominate; agriculture, cities, stable climate.

Anthropocene (proposed)

Modern human impact on Earth's systems and climate.

6 Characteristics of Mammals

Lactation; hair or fur; single bone in lower jaw; aortic arch bends left; three middle ear bones (malleus, incus, stapes); diaphragm for efficient breathing.

5 Characteristics of Primates

Post-orbital bar; nails instead of claws; opposable thumbs or toes; forward-facing eyes for depth perception; petrosal auditory bulla.

r-selected

Many offspring, fast maturity, little parental care, short lifespan.

K-selected

Few offspring, slow maturity, high parental care, long lifespan.

Cladistic classification

Based on derived traits; example: haplorhines; traits include post-orbital closure, shorter snout.

Gradistic classification

Based on ancestral traits; example: strepsirhines; traits include long snout, post-orbital bar.

Tarsier taxonomy

Gradistically prosimian, cladistically haplorhine.

Strepsirhine traits

Long snout, wet nose (rhinarium), tooth comb, grooming claw, small brain, tapetum lucidum, no post-orbital closure.

Haplorhine traits

Short snout, dry nose, post-orbital closure, large brain, no tooth comb, no grooming claw, no tapetum lucidum.

Tarsier traits

Has grooming claw, no tooth comb, more like haplorhines overall.

New World Monkeys

3 premolars, flat outward-facing nose, prehensile tails.

Old World Monkeys

2 premolars, downward-facing nose, non-prehensile tails.

Ape characteristics

No tails; Y-5 molars; larger brains; more flexible shoulders.

Plesiadapiforms

Not true primates.

Adapids

Lemur-like; first true primates.

Omomyids

Tarsier-like; includes Ida fossil.

Parapithecids

Ancestors to New World monkeys.

Propliopithecids

Ancestors to Catarrhines.

Aegyptopithecus

Early Catarrhine example.

Proconsul

First ape-like primate.

Oreopithecus

European ape, evolutionary dead end.

Dryopithecus

European ape.

Sivapithecus

Ancestor of modern orangutans.

Gigantopithecus

Giant extinct ape; mandible found.

Allopatric speciation

Populations separated by geography (e.g., chimps and bonobos).

Parapatric speciation

Overlapping populations with hybrid zones (e.g., baboons).

Sympatric speciation

Evolve in same area, different niches (e.g., bamboo lemurs).

Relative dating

Uses stratigraphy or fossils to determine age order; not exact.

Absolute dating

Uses radiometric methods (radiocarbon, K-Ar) for actual dates.

Best method for million-year fossils

Potassium-argon dating.

Human-chimp divergence

8-10 million years ago.

Lemur diversity

Isolated on Madagascar; no competition → many ecological niches.

Homology

Shared traits due to common ancestry (e.g., bat and human forelimbs).

Homoplasy

Similar traits without shared ancestry (e.g., bat and bird wings).

Convergent evolution

Unrelated species evolve similar traits (e.g., sharks and dolphins).

Parallel evolution

Closely related species evolve similar traits after divergence (e.g., bamboo lemurs, colobus monkeys).

Arboreal Hypothesis

Primates evolved traits for life in trees (grasping hands, nails, forward eyes).

Visual Predation Hypothesis

Traits evolved for hunting insects with depth perception.

Angiosperm Radiation Hypothesis

Traits evolved alongside flowering plants (color vision, grasping hands).

Vertical clingers and leapers

Long legs, short arms; leap between trees (e.g., tarsiers).

Arboreal quadrupedalism

Move on all fours in trees; long tails (e.g., capuchins).

Terrestrial quadrupedalism

Walk on all fours on ground (e.g., baboons).

Suspensory locomotion / brachiation

Swing beneath branches; long arms (e.g., gibbons).

Knuckle-walking

Weight supported on bent fingers (e.g., chimps, gorillas).

Insectivore diet

Insects; sharp cusps, shearing crests.

Frugivore diet

Fruits; broad incisors, low rounded molars.

Gumnivore diet

Tree sap; projecting incisors, claws.

Folivore diet

Leaves; high-cusped molars, small incisors.

Omnivore diet

Mixed; generalized teeth.

Infant parking

Leave infants while foraging.

Alloparenting

Helpers care for infants.

Maternal care

Mother raises offspring.

Paternal care

Father participates.

Infanticide

Males kill infants to bring females into estrus.

Primate threats

Hunting, deforestation, pet trade, habitat loss.

Sexual selection

Female choice drives evolution of male traits (bright colors, displays).

Macaque culture

Wash sweet potatoes, soak in hot springs, stack rocks.

Chimpanzee/bonobo tool use

Fish for insects.

Capuchin tool use

Crack nuts with tools.

Orangutan tool use

Use leaves as tools or bandages.

Solitary social system

Live alone (orangutans).

Monogamous social system

One male and one female pair.

Extra-pair copulation

Mating outside pair bond.

Polygyny

One male, multiple females (gorillas).

Polygamy

Multiple males and females (baboons).

Polyandry

One female, multiple males (tamarins).

Fission-fusion

Groups split and merge (chimps, bonobos).

Diurnal

Active during the day.

Nocturnal

Active at night.

Cathemeral

Active day and night (lemurs).

Crepuscular

Active at dawn and dusk.

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