Www.cengage.com/biology/starr Albia Dugger Miami Dade College Cecie Starr Christine Evers Lisa Starr Chapter 16 Evidence of Evolution (Sections 16.6 -

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Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

Chapter 16Evidence of Evolution

(Sections 16.6 - 16.9)

16.6 Putting Time Into Perspective

• Transitions in the fossil record are boundaries for great intervals of the geologic time scale

• geologic time scale • Chronology of Earth’s history• Correlates geologic and evolutionary events

The Geologic Time Scale

Sedimentary Rock in the Grand Canyon

ANIMATION: Geologic time scale

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Key Concepts

• Evidence From Fossils• The fossil record provides physical evidence of past

changes in many lines of descent• We use the property of radioisotope decay to determine

the age of rocks and fossils

16.7 Drifting Continents,Changing Seas

• The theory that all continents today were once part of the supercontinent Pangea explains why the same fossils occur in sedimentary rock on both sides of the Atlantic Ocean

• Pangea • Supercontinent that formed about 237 million years ago

and broke up about 152 million years ago

Plate Tectonics

• Movements of Earth’s tectonic plates carry land masses to new positions, which have profound impacts on evolution

• plate tectonics •Theory that Earth’s outer layer of rock is cracked into plates, the slow movement of which rafts continents to new locations over geologic time•Supported by magnetic polarity of igneous rocks

Mechanisms of Plate Tectonics

• New crust spreads outward from oceanic ridges, forcing tectonic plates away from the ridge and into trenches

Fig. 16.12.1-4, p. 248

fault hot spottrench trenchridge123 4

Mechanisms of Plate Tectonics

ANIMATION: Plate margins

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An Older Supercontinent

• Identical layers of rock around the Southern Hemisphere hold matching fossils of organisms that were extinct millions of years before Pangea formed

• An older supercontinent, Gondwana, included most land masses that are now in the Southern Hemisphere, India and Arabia

• Gondwana • Supercontinent that existed before Pangea, more than 500

million years ago

The Drifting Continents

• Major evolutionary forces: •Gondwana broke up in the Silurian•Pangea formed in the Triassic, broke up in the Jurassic

Key Concepts

• Evidence From Biogeography• Geologic events have influenced evolution• Correlating geologic and evolutionary events helps explain

the distribution of species, past and present

16.8 Similarities in Body Form and Function

• Clues about the history of a lineage may be found in body form, function, or biochemistry

• Similarities in structure of body parts often reflect shared ancestry – in such cases, comparative morphology can be used to unravel evolutionary relationships

Morphological Divergence

• Homologous structures (body parts that appear different in different lineages, but are similar in some underlying aspect of form) are evidence of a common ancestor

• Body parts become modified to a different size, shape, or function in different lineages by morphological divergence

• Example: Limb bones of all modern land vertebrates originated from a family of ancient “stem reptiles”

Key Terms

• homologous structures • Similar body parts that evolved in a common ancestor

• morphological divergence• Evolutionary pattern in which a body part of an ancestor

changes in its descendants

Morphological Divergence

• Number and position of many skeletal elements were preserved when diverse forms evolved

• Certain bones were lost over time in some of the lineages

Fig. 16.14, p. 250elephant

human

bat

porpoise

penguin

chicken

pterosaur

stem reptile5

123

4

5

12

34

5

12

3 4

1

2 3

32

54

2

3

1

4

23

1

Morphological Divergence

Morphological Convergence

• Analogous structures are body parts that look alike in different lineages but did not evolve in a common ancestor

• They evolved separately after the lineages diverged (as adaptations to the same environmental pressures) by the process of morphological convergence

• Example: Bird, bat, and insect wings all perform the same function (flight) but the wing structures are not homologous

Key Terms

• analogous structures • Similar body structures that evolved separately in different

lineages

• morphological convergence • Evolutionary pattern in which similar body parts evolve

separately in different lineages

Morphological Convergence

Fig. 16.15a, p. 251

Morphological Convergence

Fig. 16.15b, p. 251

Morphological Convergence

Fig. 16.15c, p. 251

Morphological Convergence

Fig. 16.15d, p. 251

Morphological Convergence

Fig. 16.15d, p. 251

Insects Bats Humans Crocodiles Birds

wings

wings wings

limbs with 5 digitsD

Morphological Convergence

16.9 Similarities in Patterns of Development

• Similar patterns of embryonic development reflect shared ancestry

• Master genes that control embryonic development patterns have changed very little or not at all over evolutionary time

• Master genes with similar sequence and function in different lineages are strong evidence that those lineages are related

Similar Genes in Plants

• Master genes called homeotic genes guide formation of specific body parts during development

• Example: The Apetala1 gene affects formation of petals across many different lineages, so this gene probably evolved in a shared ancestor

Developmental Comparisons in Animals

• Embryos of many vertebrate species develop in similar ways

• All vertebrates go through a stage in which they have four limb buds, a tail, and a series of somites

Fig. 16.16a, p. 252

Developmental Comparisons in Animals

Fig. 16.16b, p. 252

Developmental Comparisons in Animals

Fig. 16.16c, p. 252

Developmental Comparisons in Animals

Fig. 16.16d, p. 252

Developmental Comparisons in Animals

Fig. 16.16e, p. 252

Developmental Comparisons in Animals

Variations in Development

• Differences are brought about by variations in expression patterns of master genes that govern development

• Example: • The pattern of expression of Hox master genes

determines particular zones along the body axis• In insects, the Hox gene antennapedia, determines where

legs develop on the thorax• A vertebrate version of antennapedia, the Hoxc6 gene,

causes a vertebra to develop ribs as part of the back

Expression of Antennapedia

• A mutation that causes antennapedia to be expressed in embryonic tissues of a Drosophila’s head (left) causes legs to form there too (right)

Fig. 16.17a, p. 252

Expression of Antennapedia

Fig. 16.17b, p. 252

Expression of Antennapedia

Expression of Hox6

• Chicks (left) have 7 vertebrae in their back and 14-17 in their neck; snakes (right) have more than 450 back vertebrae

Forever Young

• Mutations that alter rate of development may allow juvenile traits to persist into adulthood

• Example:• At early stages of development, chimpanzee and human

skulls appear quite similar• Different parts develop at different rates• A human adult skull is proportioned more like the infant

chimpanzee skull than the adult chimpanzee skull

Proportional Changes During Skull Development

Fig. 16.19, p. 253

proportions in infant

proportions in infantadult

adult

A

B

Proportional Changes During Skull Development

Fig. 16.19a, p. 253

Proportional Changes During Skull Development

Fig. 16.19a, p. 253

proportions in infantadult

A

Proportional Changes During Skull Development

Fig. 16.19b, p. 253

Proportional Changes During Skull Development

Fig. 16.19b, p. 253

proportions in infant adultB

Proportional Changes During Skull Development

ANIMATION: Mutation and proportional changes

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Key Concepts

• Evidence in Form and Function• Different lineages may have similar body parts that reflect

descent from a shared ancestor• Lineages with common ancestry often develop in similar

ways

Reflections of a Distant Past (revisited)

• The K–T boundary layer, an unusual clay that formed 65 million years ago, is rich in iridium, an element rare on Earth’s surface but common in asteroids

• Scientists found a huge crater, about 65 million years old, off the coast of Mexico’s Yucatán Peninsula – evidence of an asteroid impact that may have caused extinctions