1. Chapter 16 Evidence of Evolution
(Sections ) 1

2. 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

3. The Geologic Time Scale
Figure The geologic time scale correlated with sedi-mentary rock exposed by erosion in the Grand Canyon. A Transitions between layers of sedimentary rock mark great time spans in Earth’s history (not to the same scale). mya: millions of years ago. Dates are from the International Commission on Stratigraphy, 2007.
B We can reconstruct some of the events in the history of life by studying rocky clues in the layers. Here, the red triangles mark times of great mass extinctions. ‘First appearance’ refers to appearance in the fossil record, not necessarily the first appearance on Earth; we often discover fossils that are significantly older than previously discovered specimens.
C Each rock layer has a composition and set of fossils that reflect events during its deposition. For example, Coconino Sandstone, which stretches from California to Montana, is mainly weathered sand. Ripple marks and reptile tracks are the only fossils in it. Many think it is the remains of a vast sand desert, like the Sahara is today.

4. Sedimentary Rock in the Grand Canyon
Figure The geologic time scale correlated with sedi-mentary rock exposed by erosion in the Grand Canyon. A Transitions between layers of sedimentary rock mark great time spans in Earth’s history (not to the same scale). mya: millions of years ago. Dates are from the International Commission on Stratigraphy, 2007.
B We can reconstruct some of the events in the history of life by studying rocky clues in the layers. Here, the red triangles mark times of great mass extinctions. ‘First appearance’ refers to appearance in the fossil record, not necessarily the first appearance on Earth; we often discover fossils that are significantly older than previously discovered specimens.
C Each rock layer has a composition and set of fossils that reflect events during its deposition. For example, Coconino Sandstone, which stretches from California to Montana, is mainly weathered sand. Ripple marks and reptile tracks are the only fossils in it. Many think it is the remains of a vast sand desert, like the Sahara is today.

5. ANIMATION: Geologic time scale
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6. 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

7. 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

8. 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

9. Mechanisms of Plate Tectonics
New crust spreads outward from oceanic ridges, forcing tectonic plates away from the ridge and into trenches

10. Mechanisms of Plate Tectonics3 2 1 4
fault
trench
ridge
hot spot
trench
Figure Plate tectonics. Huge pieces of Earth’s outer rock layer slowly drift apart and collide. As the plates move, they convey continents around the globe. The current configuration of the plates is shown in Appendix VIII.
Fig , p. 248

11. ANIMATION: Plate margins
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12. 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

13. The Drifting Continents
Major evolutionary forces:
Gondwana broke up in the Silurian
Pangea formed in the Triassic, broke up in the Jurassic
Figure A series of reconstructions of the drifting continents. A The supercontinent Gondwana (yellow) had begun to break up by the Silurian. B The supercontinent Pangea formed during the Triassic, then C began to break up in the Jurassic. D K–T boundary. E The continents reached their modern configuration in the Miocene.

14. Key Concepts Evidence From Biogeography
Geologic events have influenced evolution
Correlating geologic and evolutionary events helps explain the distribution of species, past and present

15. 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

16. 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”

17. 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

18. 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

19. Morphological Divergence2 1 3
pterosaur 4 1 2
chicken 3 2 3
penguin 1 2 1 3 4
stem reptile 5 4
porpoise 2 3 5 1 2
Figure Morphological divergence among vertebrate forelimbs, starting with the bones of a stem reptile. The number and position of many skeletal elements were preserved when these diverse forms evolved; notice the bones of the forearms. Certain bones were lost over time in some of the lineages (compare the digits numbered 1 through 5). The drawings are not to the same scale.
bat 3 4 1 5 2 3 4 5
human
elephant
Fig , p. 250

20. 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

21. 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

22. Morphological Convergence

23. Morphological Convergence
Figure Morphological convergence. The flight surfaces of a bat wing A, a bird wing B, and an insect wing C are analogous structures. D The independent evolution of wings in the three separate lineages that led to bats, birds, and insects. You will read more about diagrams that show evolutionary relationships in Section
Fig a, p. 251

24. Morphological Convergence
Figure Morphological convergence. The flight surfaces of a bat wing A, a bird wing B, and an insect wing C are analogous structures. D The independent evolution of wings in the three separate lineages that led to bats, birds, and insects. You will read more about diagrams that show evolutionary relationships in Section
Fig b, p. 251

25. Morphological Convergence
Figure Morphological convergence. The flight surfaces of a bat wing A, a bird wing B, and an insect wing C are analogous structures. D The independent evolution of wings in the three separate lineages that led to bats, birds, and insects. You will read more about diagrams that show evolutionary relationships in Section
Fig c, p. 251

26. Morphological Convergence
Figure Morphological convergence. The flight surfaces of a bat wing A, a bird wing B, and an insect wing C are analogous structures. D The independent evolution of wings in the three separate lineages that led to bats, birds, and insects. You will read more about diagrams that show evolutionary relationships in Section
Fig d, p. 251

27. Morphological Convergence
Insects
Bats
Humans
Crocodiles
Birds
wings
wings
wings
Figure Morphological convergence. The flight surfaces of a bat wing A, a bird wing B, and an insect wing C are analogous structures. D The independent evolution of wings in the three separate lineages that led to bats, birds, and insects. You will read more about diagrams that show evolutionary relationships in Section
limbs with 5 digits D
Fig d, p. 251

28. 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

29. 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

30. 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

31. Developmental Comparisons in Animals
Figure Visual comparison of vertebrate embryos. All vertebrates go through an embryonic stage in which they have four limb buds, a tail, and divisions called somites along their back. Embryos left to right: human, mouse, bat, chicken, alligator.
Fig a, p. 252

32. Developmental Comparisons in Animals
Figure Visual comparison of vertebrate embryos. All vertebrates go through an embryonic stage in which they have four limb buds, a tail, and divisions called somites along their back. Embryos left to right: human, mouse, bat, chicken, alligator.
Fig b, p. 252

33. Developmental Comparisons in Animals
Figure Visual comparison of vertebrate embryos. All vertebrates go through an embryonic stage in which they have four limb buds, a tail, and divisions called somites along their back. Embryos left to right: human, mouse, bat, chicken, alligator.
Fig c, p. 252

34. Developmental Comparisons in Animals
Figure Visual comparison of vertebrate embryos. All vertebrates go through an embryonic stage in which they have four limb buds, a tail, and divisions called somites along their back. Embryos left to right: human, mouse, bat, chicken, alligator.
Fig d, p. 252

35. Developmental Comparisons in Animals
Figure Visual comparison of vertebrate embryos. All vertebrates go through an embryonic stage in which they have four limb buds, a tail, and divisions called somites along their back. Embryos left to right: human, mouse, bat, chicken, alligator.
Fig e, p. 252

36. 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

37. 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)

38. Expression of Antennapedia
Figure Expression of the antennapedia gene in the embryonic tissues of the insect thorax causes legs to form. Normally, the gene is never expressed in cells of any other tissue. A mutation that causes antennapedia to be expressed in the embryonic tissues of a Drosophila’s head (left) causes legs to form there too (right).
Fig a, p. 252

39. Expression of Antennapedia
Figure Expression of the antennapedia gene in the embryonic tissues of the insect thorax causes legs to form. Normally, the gene is never expressed in cells of any other tissue. A mutation that causes antennapedia to be expressed in the embryonic tissues of a Drosophila’s head (left) causes legs to form there too (right).
Fig b, p. 252

40. Expression of Hox6
Chicks (left) have 7 vertebrae in their back and in their neck; snakes (right) have more than 450 back vertebrae
Figure An example of comparative embryology. Expression of the Hoxc6 gene is indicated by purple stain in two vertebrate embryos, chick (left) and garter snake (right). Expression of this gene causes a vertebra to develop ribs as part of the back. Chickens have 7 vertebrae in their back and 14 to 17 vertebrae in their neck; snakes have upwards of 450 back vertebrae and essentially no neck.

41. 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

42. Proportional Changes During Skull Development

43. Proportional Changes During Skull Development
adult A
proportions in infant
Figure Morphological differences between two primates. These skulls are depicted as paintings on a rubber sheet divided into a grid. Stretching the sheets deforms the grid. Differences in how they are stretched are analogous to different growth patterns. Shown here, proportional changes during skull development in A the chimpanzee and B the human. Chimpanzee skulls change more than human skulls, so the relative proportions in bones of adult and infant humans are more similar than those of adult and infant chimpanzees. B
adult
proportions in infant
Fig , p. 253

44. Proportional Changes During Skull Development
Figure Morphological differences between two primates. These skulls are depicted as paintings on a rubber sheet divided into a grid. Stretching the sheets deforms the grid. Differences in how they are stretched are analogous to different growth patterns. Shown here, proportional changes during skull development in A the chimpanzee and B the human. Chimpanzee skulls change more than human skulls, so the relative proportions in bones of adult and infant humans are more similar than those of adult and infant chimpanzees.
Fig a, p. 253

45. Proportional Changes During Skull Development
adult
Figure Morphological differences between two primates. These skulls are depicted as paintings on a rubber sheet divided into a grid. Stretching the sheets deforms the grid. Differences in how they are stretched are analogous to different growth patterns. Shown here, proportional changes during skull development in A the chimpanzee and B the human. Chimpanzee skulls change more than human skulls, so the relative proportions in bones of adult and infant humans are more similar than those of adult and infant chimpanzees. A
proportions in infant
Fig a, p. 253

46. Proportional Changes During Skull Development
Figure Morphological differences between two primates. These skulls are depicted as paintings on a rubber sheet divided into a grid. Stretching the sheets deforms the grid. Differences in how they are stretched are analogous to different growth patterns. Shown here, proportional changes during skull development in A the chimpanzee and B the human. Chimpanzee skulls change more than human skulls, so the relative proportions in bones of adult and infant humans are more similar than those of adult and infant chimpanzees.
Fig b, p. 253

47. Proportional Changes During Skull Development
Figure Morphological differences between two primates. These skulls are depicted as paintings on a rubber sheet divided into a grid. Stretching the sheets deforms the grid. Differences in how they are stretched are analogous to different growth patterns. Shown here, proportional changes during skull development in A the chimpanzee and B the human. Chimpanzee skulls change more than human skulls, so the relative proportions in bones of adult and infant humans are more similar than those of adult and infant chimpanzees.
adult B
proportions in infant
Fig b, p. 253

48. ANIMATION: Mutation and proportional changes
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49. 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

50. 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