Chapter 16 Evidence of Evolution (Sections 16.6 - 16.9) 1

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 Figure 16.11 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.

Sedimentary Rock in the Grand Canyon Figure 16.11 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.

ANIMATION: Geologic time scale To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

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

Mechanisms of Plate Tectonics 3 2 1 4 fault trench ridge hot spot trench Figure 16.12 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. 16.12.1-4, p. 248

ANIMATION: Plate margins To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

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 Figure 16.13 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.

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

Morphological Divergence 2 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 16.14 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. 16.14, p. 250

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

Morphological Convergence Figure 16.15 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 17.14. Fig. 16.15a, p. 251

Morphological Convergence Figure 16.15 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 17.14. Fig. 16.15b, p. 251

Morphological Convergence Figure 16.15 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 17.14. Fig. 16.15c, p. 251

Morphological Convergence Figure 16.15 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 17.14. Fig. 16.15d, p. 251

Morphological Convergence Insects Bats Humans Crocodiles Birds wings wings wings Figure 16.15 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 17.14. limbs with 5 digits D Fig. 16.15d, p. 251

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

Developmental Comparisons in Animals Figure 16.16 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. 16.16a, p. 252

Developmental Comparisons in Animals Figure 16.16 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. 16.16b, p. 252

Developmental Comparisons in Animals Figure 16.16 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. 16.16c, p. 252

Developmental Comparisons in Animals Figure 16.16 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. 16.16d, p. 252

Developmental Comparisons in Animals Figure 16.16 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. 16.16e, p. 252

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)

Expression of Antennapedia Figure 16.17 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. 16.17a, p. 252

Expression of Antennapedia Figure 16.17 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. 16.17b, p. 252

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 Figure 16.18 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.

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

Proportional Changes During Skull Development adult A proportions in infant Figure 16.19 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. 16.19, p. 253

Proportional Changes During Skull Development Figure 16.19 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. 16.19a, p. 253

Proportional Changes During Skull Development adult Figure 16.19 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. 16.19a, p. 253

Proportional Changes During Skull Development Figure 16.19 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. 16.19b, p. 253

Proportional Changes During Skull Development Figure 16.19 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. 16.19b, p. 253

ANIMATION: Mutation and proportional changes To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

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