1 - 100 pgs

FROM TREE SHREW TO APE

CHAPTER OBJECTIVES

By the end of this chapter you should be able to:
A. Explain how the major changes in the position of the continents and world climates have influenced the course of primate evolution.
B. Describe how paleontologists establish the age of fossils.
C. Assess what we know about the earliest members of the primate lineage.
D. Identify when and where apelike primates first appear in the fossil record.

1. Historical Context of Primate Evolution

1.1 Permian and Early Triassic Periods

  • During the Permian and early Triassic periods, the Earth's fauna was dominated by therapsids.

  • Therapsids: A diverse group of reptiles featuring traits linking them to modern mammals, such as warm-bloodedness and hair covering (see Figure 9.1).

  • The extinction of most therapsid groups at the end of the Triassic allowed dinosaurs to fill ecological niches for large, terrestrial animals.

  • One lineage of therapsids diversified into the first true mammals, which were small, nocturnal creatures that likely fed on seeds and insects, featuring internal fertilization and egg-laying capabilities.

  • By the end of the Mesozoic era (65 million years ago), placental and marsupial mammals had evolved.

  • The extinction of dinosaurs initiated the Cenozoic era and spurred the radiation of mammals, including modern descendants like horses, bats, and primates.

  • Early mammals likely resembled contemporary tree shrews (see Figure 9.2).

1.2 Key Thematic Outline

  1. Continental Drift and Climate Change (p. 212).

  2. Methods of Paleontology (p. 213).

  3. Evolution of Early Primates (p. 218).

  4. Haplorrhine Diversification (p. 222).

  5. Emergence of the Apes (p. 227).

2. Geologic Timescale

2.1 Table 9.1: The Geologic Timescale

  • Cenozoic Era:

    • Quaternary: Holocene (0.012 Ma), Pleistocene (2.6 Ma).

    • Note: Origins of agriculture and Homo sapiens.

    • Tertiary:

    • Pliocene (5 Ma). Miocene (23 Ma), Oligocene (34 Ma), Eocene (54 Ma), Paleocene (66 Ma).

    • Dominance of angiosperms, mammals, birds, and insects.

  • Mesozoic Era:

    • Cretaceous (136 Ma): Rise of angiosperms, dinosaurs extinct.

    • Jurassic (190 Ma): Abundance of dinosaurs, first birds.

    • Triassic (225 Ma): First appearances of mammals and dinosaurs.

  • Paleozoic Era:

    • Permian (280 Ma): Expansion of reptiles, decline of amphibians, last trilobites.

    • Carboniferous (345 Ma): Age of amphibians; first reptiles.

    • Devonian (395 Ma): Age of fishes; first amphibians, insects.

2.2 The Animal Kingdom Over Time

  • Certain lessons regarding evolutionary history can be traced through paleontology which reveals habitats and environments in which early primates lived and evolved.

3. Fossil Evidence and Paleontology

3.1 Fossils and Paleontology

  • Fossils: Mineralized remains of once-living organisms, potentially preserved for millions of years.

  • Paleontologists: Scientists that study, describe, and interpret fossils.

    • Fossils inform understanding of ancient environments and species adaptations to climate.

3.2 Radiometric Dating Methods

  • Several radiometric methods are employed to estimate the age of fossils:

    1. Potassium-Argon Dating: Dates volcanic rocks and related fossil materials.

    2. Carbon-14 Dating: Used for dating relatively young fossils, less than 40,000 years old.

    3. Thermoluminescence Dating: Measures trapped electrons in minerals to estimate age.

    4. Electron Spin Resonance Dating: Determines the age of materials based on electron traps.

    5. Uranium-Lead Dating: Primarily used for dating older geological formations.

4. Continental Drift and Climate Change

4.1 Importance of Continental Drift

  • Continental Drift: The slow movement of the Earth’s plates has significantly influenced climatic conditions and subsequently, evolution.

    • Example: Pangaea’s separation altered oceanic currents and climates, affecting species migrations and environmental adaptations.

  • Climate Change: Shifting climates throughout the ages have dictated the adaptation processes in evolving primates, introducing variability in evolutionary pathways.

5. The Evolution of Early Primates

5.1 Evolution of Angiosperms and Primates

  • The emergence of flowering plants (angiosperms) during the Mesozoic revolutionized ecological niches.

  • Primates evolved in connection with these changes, adapting to various diets including fruits and insects.

5.2 Plesiadapiforms

  • Plesiadapiforms: Group considered a potential ancestor to primates, existing from the Paleocene epoch (66-54 Ma).

    • Characteristics include a well-developed sense of smell, varied diet, claws, and small body size.

  • The species Carpolestes simpsoni, for example, featured an opposable big toe and traits indicating fruit-eating behavior (see Figure 9.7).

5.3 Eocene Epoch Primates

  • Eocene primates exhibited key traits of modern primates, such as grasping hands and forward-facing eyes.

  • Faunal diversity increased during the Eocene, producing many adaptations among early primate groups (Figures 9.9, 9.10).

6. Haplorrhine Diversification & Emergence of Apes

6.1 Evolution of Haplorrhines

  • The Oligocene Epoch saw climate shifts that influenced the demise and relocation of primate species.

  • The earliest unambiguous haplorrhines emerged from the Fayum Depression of Egypt.

6.2 Emergence of Apes

  • Apes began to diverge during the late Oligocene, with fossil evidence suggesting diversity and adaptation in evolving environments (Figure 9.22).

6.3 Adaptations Supporting Suspensory Locomotion

  • Early hominoids specialized in anatomical features enabling efficient movement below branches, differentiating them from ancestral monkeys (Figure 9.21).