Primate Origins

Three major hypotheses explaining primate evolution:

1. Arboreal Hypothesis

   • Traits evolved for tree locomotion

   • Grasping extremities, flexible joints, forward-facing eyes for depth perception

   • Reduced olfactory system, enhanced vision

2. Visual Predation Hypothesis

   • Adaptations linked to insect hunting

   • Grasping extremities for catching prey

   • Enhanced vision for prey detection

3. Angiosperm-Primate Coevolution Hypothesis

   • Primate traits evolved alongside flowering plants

   • Color vision, grasping hands/feet, omnivory to access fruit, nectar, and seeds

• Compromise Theory: Combination of all three hypotheses suggests early primates engaged in both fruit consumption and insect predation

Geological Timeline of Primate Evolution

• Mesozoic Era (~251-65.5 mya)

  • Age of dinosaurs

  • Mammals were small, nocturnal

• Cenozoic Era (~65 mya – Present)

  • Most primate evolution occurred

  • Split into 7 epochs:

Cenozoic Epochs & Primate Evolution

1. Paleocene (65-55.8 mya)

   • First archaic primates (plesiadapiforms)

2. Eocene (55.8-33 mya)

   • First true primates (euprimates)

   • Early strepsirrhines and haplorhines

3. Oligocene (33-23 mya)

   • Early catarrhines, precursors to monkeys & apes

4. Miocene (23-5.3 mya)

   • First monkeys and apes

   • Human-like creatures emerge

5. Pliocene (5.3-2.6 mya)

   • Early hominin diversification

6. Pleistocene (2.6-0.105 mya)

   • Evolution of early Homo species

7. Holocene (0.105 mya – Present)

   • Modern humans

Paleocene and Primate Evolution

• K-T extinction (~66 mya):

  • 70% of species extinct, ecological niches opened

  • Angiosperms expanded, supporting early primates

• First primates emerged around the Paleocene-Cretaceous transition (~66 mya)

Estimating Primate Origins

• Fossil Record:

  • Crown group: Definite primates with derived traits

  • Stem group: Precursor species lacking distinct traits

  • First primates likely emerged earlier than fossil evidence suggests

• Molecular Clock:

  • Uses DNA mutations to estimate species divergence

  • Tends to overestimate divergence compared to fossils

Plesiadapiforms – Early Primate Ancestors

• Considered "archaic primates", not true primates

• Three main families:

  1. Purgatoriidae – Earliest primates, small, arboreal

  2. Plesiadapidae – Rodent-like incisors, likely folivorous

  3. Carpolestidae – Arboreal, opposable grasping toe

• Key Traits:

  • Claws instead of nails

  • No post-orbital bar

  • Supports Arboreal Hypothesis

Eocene – Rise of True Primates (Euprimates)

• Eocene (55.8-33 mya): Warmer, more tropical forests

• Euprimate traits:

  • Forward-facing eyes, greater brain size, opposable big toe, nails (not claws)

Two Main Euprimate Groups

1. Adapoids (Apoidea) – Lemur-like

   • Diurnal, herbivorous, larger body size

   • Considered stem group for strepsirrhines

   • Darwinius ("Ida") – One of the most complete early primate fossils

2. Omomyoids (Omomyoidea) – Tarsier-like

   • Nocturnal, small-bodied, frugivorous/insectivorous

   • Possible ancestors to haplorhines (monkeys, apes, humans)

Regional Omomyoid Evolution

• Asia: Archicebus – Early diurnal insectivore

• Europe: Necrolemur – Possible tarsier ancestor, leaper adaptations

• North America: Nocturnal, frugivorous species

Summary of Key Takeaways

• Primate evolution theories suggest adaptations for trees, insect predation, and fruit consumption

• Cenozoic Era (~65 mya-Present) was the key period for primate diversification

• Paleocene (~66 mya): First archaic primates appeared

• Eocene (~55.8 mya): Rise of true primates (euprimates)

• Adapoids → Strepsirrhine ancestors (lemur-like)

• Omomyoids → Possible Haplorhine ancestors (tarsier-like, early monkeys & apes)