Primate Evolution Notes

Chapter 8: Primate Evolution

• Chapter 8 focuses on primate evolution based on fossil evidence.

• It explores the evolution of the primate line using fossils found over the last 100-200 years.

• The chapter highlights various fossil species.

• Following chapters will focus on hominins, which are bipedal line of fossils.

• Understanding fossil formation and dating processes is crucial.

Cuvier and Catastrophism

• Cuvier, mentioned in Chapter 2, is a founder of fossil science.

• He discovered fossils of extinct organisms and developed the concept of extinction.

• Cuvier also found some fossils in the primate line.

Earliest Primates

• Primates possibly started evolving around 65 million years ago.

• This led to Priscillians (old term for Strepsirrhines).

• Strepsirrhines are lemurs and lorises.

• Lemurs and lorises look different because they are tied to the most primitive evolving line of primates.

• Around 65 million years ago, when dinosaurs went extinct, primates filled various ecological niches.

• Old World monkeys branched off about 25 million years ago.

• New World monkeys branched off about 35 million years ago.

• Lesser apes branched off about 18 million years ago.

• Great apes branched off about 14 million years ago.

• Gorillas: 12 million years ago.

• Chimps: 8-10 million years ago.

• Hominins (leading to Homo sapiens) branched off from apes about 8-9 million years ago.

Emergence of Primates

• Primates started filling ecological niches after the extinction of dinosaurs.

• Hypotheses for primate flourishing around 65 million years ago:

  • Arboreal hypothesis: Reliance on trees.

  • Visual predation hypothesis: Reliance on vision over smell for hunting.

  • Angiosperm radiation hypothesis (or Angiosperm primate coevolution hypothesis): Success related to specific environments.

Debate on Earliest Primates

• Early belief: Plesiadapaforms were the earliest primates.

• Plesiadapaforms had primate-like features in their hands but lacked a post-orbital bar in their skull.

• Post-orbital bar: bony structure alongside the eye socket

• Lemurs have a post-orbital bar, but it's not a complete enclosure.

• Plesiadapaforms lack this, having a completely open area behind the eye socket.

• Around 60 years ago, the idea of Plesiadapaforms as the oldest primates started to decline.

• U. Primates (Euprimates): Dappets and Omameids:

  • Now generally considered the first true primates.

• Textbook indicates shift back to considering Plesiadapaforms as potentially the oldest primates.

• Purgatoryus, a Plesiadapaform, is considered one of the earliest primates.

• Paleocene Epoch: specifically referring to Plizia Dapliforms

Geological Time Terms (Epochs)

• Eocene: Older/oldest epoch.

• Oligocene.

• Miocene.

Important Fossil Finds

• Darwin (fossil find): Discovered in the early 2000s, considered part of the Strepsirrhine branch

• Arches Sepis:

  • Generally considered one of the earliest Haplorhines.

  • May have given rise to all Haplorhines.

  • Dated to about 55 million years ago, found in China.

  • Linked to modern Haplorhines through ankle bone and teeth features.

• Yosimus (Eosimius):

  • Also called the dawn monkey, found in China about 42 million years. ago.

  • May have been the first anthropoid (monkeys, apes, and humans).

  • Found during the Eocene epoch.

  • Attributed as the first anthropoid due to ankle bone similarity to modern anthropoids (like baboons) compared to Tarsiers.

Significance of the Phi M (Faiyum) Depression

• Located in Egypt.

• 37-29 million years ago (Oligocene epoch).

• Very different ecological look: wetlands instead of desert.

• Important area for fossil finds (primates and non-primates).

• Egyptopithecus: Important early primate fossil dated between 32 and 29 million years ago.

New World Primates

• Found in North and South America.

• Debate on how they arrived in the New World:

  1. Evolved directly from early Plesiadapaforms in North America (unlikely due to a gap in the fossil record).

  2. Came from the Old World (more evidence of primate evolution in the Old World).

  3. Coastal route through Antarctica.

  4. Evolved completely and independently.

• Genetic evidence discounts the fourth hypothesis: New World monkeys originated from Old World monkeys.

• Most likely, they crossed the Atlantic Ocean through waterway path.

Rafting

• Animals get stuck on floating vegetation and drift across the ocean by chance.

• This may have been how primates from the Old World reached South America.

• There would have been islands that were present, where, you know, at stopping off points.

Ape Beginnings

• Apes are closest relatives.

• Earliest apes evolved about 20 million years ago.

• Known as dental apes.

• Proconsul: One of the earliest types of apes.

• Lack of external tail.

• Monkey-like body plan: equal size arms and legs.

• Small in size.

Dental Apes

• Looked monkey-like except for their teeth.

• Wi-fi (Y-5) molar pattern: 5 bumps or cusps and a Y-shaped groove (seen in apes and humans).

• Wi-fi molar pattern evolved due to diet.

  • Bilophodont molar: Monkeys have this type of tooth that contains a deep groove down the middle and 4 bumps.

• Miocene apes: Proconsul is an example.

Gigantopithecus

• Extinct early ape species, but not a dental ape.

• Lived around 2 million years ago (much more recent than dental apes).

• Found in southern parts of Asia (China and India).

• Largest primate ever (8-11 feet tall when standing, up to 600 pounds).

• Walked quadrupedally but could stand.

• Lived in the same range and time period as Homo erectus.

• Possible origin of Yeti legends.