Macroevolution%20and%20the%20Early%20Primates

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Chapter 5

• Macroevolution and the Early Primates

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Chapter Outline

• What Is Macroevevolution?
• When and Where Did the First Primates Appear, and
  What Were They Like?
• When Did the First Monkeys and Apes Appear, and
  What Were They Like?

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Macroevolution

• Over time, macroevolutionary forces produce new
  species from old ones.
• Macroevolution focuses upon the formation of new
  species and on the evolutionary relationships
  between groups of species.
• Isolating mechanisms can separate breeding
  populations and lead to the appearance of new
  species.

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Isolating Mechanisms

• Geographical
• Anatomical structure
• Social and cultural concepts

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Cladogenesis
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Isolating Mechanisms

• In branching evolution, isolating mechanisms
  separate breeding populations, creating divergent
  subspecies and then divergent species.
• Geographical, biological, or social isolating
  mechanisms block gene flow between groups,
  contributing to the accumulation of genetic
  mutations in each population.
• Biological isolating mechanisms include phenomena
  such as the sterility of hybrid offspring.

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Anagenesis and Convergence

• Anagenesis
• When natural selection, over time, favors some
  variants over others.
• Creates a change in a populations average
  characteristics.
• Convergence
• Occurs when two unrelated species come to
  resemble each other owing to functional
  similarities.

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Anagenesis
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Continental Drift
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Primate Evolution

• Primates arose from a branching of mammalian
  forms that began more than 100 million years
  after the appearance of the first mammals.
• Most ecological niches that mammals have since
  occupied were
• preempted by reptiles
• nonexistent until flowering plants became
  widespread about 65 million years ago.

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Ancestral Features

• Features in the Eocene genus Adapis are found in
  prosimians today. Like modern lemurs, it has a
  postorbital bar, a bony ring around the eye
  orbit. Note that the orbit is open behind the
  ring.

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Primate Evolution

• Geological changes in the orientation and
  position of the earths continents affected the
  global climate.
• This played a key role in the evolution and
  distribution of the primates.
• The first primates were arboreal insect eaters
  and the characteristics of all primates developed
  as adaptations to this early way of life.

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Early Primates

• The earliest primates developed 60 million years
  ago in the Paleocene epoch.
• They were small arboreal creatures.
• Diverse prosimianlike forms were common in the
  Eocene across what is now North America and
  Eurasia.
• By the late Eocene, 45 million years ago, small
  primates combining prosimian and anthropoid had
  emerged.

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Location of Hominid Fossils
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Primate Evolution

• By the late Eocene small primates combining
  lemurlike and tarsierlike features with those in
  monkeys and apes developed.
• In the Miocene epoch, apes proliferated and
  spread over many parts of the Old World.
• Ancestors of large apes and humans appeared by 16
  m.y.a. and were widespread as recently as 8
  m.y.a.

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Primate Evolution

• Details of dentition suggest that hominines arose
  from these earlier apes.
• Some populations lived in parts of Africa where
  pressures existed to transform a creature just
  like it into a primitive hominine.
• Other populations remained in the forests,
  developing into todays bonobo, chimpanzee, and
  gorilla.

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