1. 23
Broad Patterns of Evolution

2. PALEONTOLOGY
Paleontology: The branch of biology that reconstructs evolutionary history by collecting and evaluating fossils
Fossils: preserved remains or impressions left by organisms from the past
The fossil record shows evidence of macroevolution, broad changes above the species level; for example:
The emergence of terrestrial vertebrates
The impact of mass extinctions
The origin of flight in birds

3. Fossils
Fossils are the remains of once-living organisms, preserved through time in sedimentary rocks.
Fossils only preserve the mineral-rich hard parts of an organism

4. Formation of the Fossil Record
In order for an organism to be fossilized, it must first be buried, after which sediments accumulate over time and harden. Erosion of the Grand Canyon has exposed layers of sedimentary rock and a record of Earth’s history.
Most fossils preserve the hard parts of organisms, those features that resist decay after death. But for organisms that do not have hard parts, there is not much of a fossil record.

5. Trace & Molecular Fossils
Tracks, footprint, and trails
Molecular fossils: DNA, proteins, lipids
Organisms that lack hard parts can leave a fossil record in two other, distinctive ways:
Trace fossils: tracks and trails
Molecular fossils: DNA, proteins, lipids

6. Iguandontid Footprints Found in 1992 at Dinosaur Ridge, Colorado
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7. Burgess Shale Preserved the deep seafloor of 505 mya
In rare circumstances, fossils can be preserved in unexpected quality. Here, a sedimentary rock formation called the Burgess Shale preserved the deep seafloor of 505 million years ago.
Preserved the deep seafloor of 505 mya

8. Coccosteus cuspidatus 400
Figure 23.3-s8
1 m
100 mya
Rhomaleosaurus
victor
175
200
0.5 m
Dimetrodon
270
Tiktaalik
300
4.5 cm
375
Coccosteus cuspidatus
400
1 cm
Hallucigenia
Figure 23.3-s8 Documenting the history of life (step 8)
500
2.5 cm
510
Dickinsonia
costata
560
Stromatolites
600
1,500
Stromatolite
cross section
3,500
Tappania
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9. The Fossil Record
Sedimentary rocks: layers solidified soil called strata and are the richest source of fossils
The fossil record indicates that there have been great changes in the kinds of organisms on Earth at different points in time
The fossil record is biased in favor of species that
Existed for a long time
Were abundant and widespread
Had mineral-rich hard parts
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10. Geologic Timescale Relative dating:
The order in which fossils appear in strata (layers) of sedimentary rock indicates relative age of fossil
Lower fossils: older
Higher fossils: more recent
Compare to index fossil…shells of marine organisms
Fossils record the evolution of life on Earth. Geologists recognized that groups of fossils change systematically from the bottom of a sedimentary rock formation to its top. It became clear that certain fossils always occur in layers that lie beneath, and so are older than, layers that contain other species. From this pattern, geologists mapped out the series of time divisions that mark Earth’s long history in the geologic timescale.

11. Radioactive Decay Absolute dating:
Uses radioactive isotopes to give the age of fossil, with <10% error, in wood and bones
Compare half-life of isotope in living organism to ratio of same isotopes in fossil
Half-life: number of years for half (50%) of the original sample to decay
While the layers of fossils in sedimentary rocks can tell us that some rocks are older than others, they themselves cannot provide an absolute age.
Calibration of the timescale became possible with the discovery of radioactive decay. Archaeologists commonly use the radioactive decay of an isotope of carbon to date wood and bone.
Cosmic radiation generates carbon-14 in the atmosphere. Through photosynthesis, carbon dioxide that is composed of carbon-14 is incorporated into wood, and animals also incorporate carbon-14 in their tissues when they eat plant material. After death, the unstable carbon-14 begins to break down, losing an electron to form nitrogen-14 (which is a stable isotope of nitrogen). Laboratory measurements have indicated that half of the carbon-14 in a sample will decay to nitrogen in 5730 years (carbon-14’s half-life).
Because carbon-14 has a short half-life, it is only useful in dating materials younger than 50,000 to 60,000 years. Archeologists generally date older samples by looking at the radioactive decay of uranium or lead.

12. Radiocarbon dating can be used to date fossils up to 75,000 years old
Figure 23.4
Radiocarbon dating can be used to date fossils up to 75,000 years old
Fraction of parent
isotope remaining
Accumulating
“daughter”
isotope 1 2
Remaining
“parent”
isotope 1 4 1 8 1 16
Figure 23.4 Radiometric dating 1 2 3 4
Time (half-lives)
For older fossils, some isotopes can be used to date volcanic rock layers above and below the fossil
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13. Fossils Frame the Geologic Record
The geologic record is a standard time scale dividing Earth’s history into 4 Eons (the Hadean, Archaean, Proterozoic, and Phanerozoic)
Origin of the earth: 4.6 bya
First prokaryotic cell: 3.5 bya; stromatolite fossils
Origin of Eukaryotes: 2 bya
The Phanerozoic eon encompasses most of the time that animals have existed on Earth
It is divided into 3 eras: the Paleozoic, Mesozoic, and Cenozoic (current time) Eras
Major boundaries between geological divisions correspond to extinction events in the fossil record
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14. Table 23.1 The geologic record
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15. Paleozoic & Mesozoic Eras
Paleozoic era: age of ancient eukaryotic life
Cambrian period: mya; Cambrian explosion= sudden increase in diversity of many animal phyla
Permian period: mya; Permian extinction= mass extinction of many marine and terrestrial organisms
Mesozoic era: age of reptiles
Jurassic period: dinosaurs abundant/diverse; NOTE: dinosaurs existed for 200 million years!
Cretaceous period: mya; Cretaceous extinction= many groups of organisms became extinct, including dinosaurs

16. Cenozoic Era Cenozoic era: age of mammals (newest era)
Paleocene epoch: mya; mammals flourished
Pliocene epoch: mya; ape-like ancestors of humans appear; Australopithicus africanus
Pleistocene epoch: 1.8 million -10,000 years ago; Ice ages; human-like hominids appear; Homo erectus. Homo Neanderthal
Holocene epoch: 10,000 years to present age; age of Homo sapiens

17. BIOGEOGRAPHY Biogeography: Geographical distribution of species
Continental drift: drifting of continents
Results from movement of plates of crust/upper mantle that float on Earth’s molten core
Called “plate tectonics”
Where 2 plates meet, many important geological phenomena occur; i.e. earthquakes, volcanoes

18. Plate Tectonics
At 3 points in time, the landmasses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago
According to the theory of plate tectonics, Earth’s crust is composed of plates floating on Earth’s mantle
Crust
Mantle
Outer core
Inner core
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19. Figure 23.8
Tectonic Plates
North
American
Plate
Eurasian Plate
Caribbean
Plate
Philippine
Plate
Juan de Fuca
Plate
Arabian
Plate
Indian
Plate
Cocos Plate
South
American
Plate
Pacific
Plate
Nazca
Plate
African
Plate
Australian
Plate
Figure 23.8 Earth’s major tectonic plates
Antarctic
Plate
Tectonic plates move slowly through the process of continental drift (movement of continents); Oceanic and continental plates can separate, slide past each other, or collide
Interactions at plate boundaries cause the formation of mountains and islands and earthquakes
Scotia Plate
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20. Pangaea Formation of Pangea……”all land”
Occurred at end of Paleozoic era (250 mya)
Supercontinent
Had tremendous environmental impact…..possibly Permian extinction?
The Earth we experience today is unlike any previous state of the planet, in terms of the location and sizes of its continents, ocean chemistry and atmospheric composition. Today, for example, the continents are distributed widely over the planet’s surface, but 290 million years ago they were clustered in a supercontinent called Pangaea.
Oxygen gas permeates most surface environments of Earth today, but 3 billion years ago, there was no O2 anywhere. And, just 20,000 years ago, 2 km of glacial ice stood where Boston lies today. Sedimentary rocks record the changing state of Earth’s surface over billions of years and show that life and environment have changed together through time, each influencing the other.
A deepening of ocean basins
A reduction in shallow water habitat
A colder and drier climate inland

21. Present Collision of India with 45 mya Eurasia Cenozoic Present-day
Figure 23.9
Present
Collision of
India with
Eurasia
45 mya
Cenozoic
North America
Eurasia
66 mya
Africa
Present-day
continents
South
India
America
Madagascar
Australia
Antarctica
Laurasia
Laurasia and
Gondwana
landmasses
135 mya
Mesozoic
Gondwana
Figure 23.9 The history of continental drift during the Phanerozoic eon
252 mya
Pangaea
The supercontinent
Pangaea
Paleozoic
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22. BREAKUP OF PANGEA Occurred during Mesozoic era (180 mya)
Pangea broke into northern (Laurasia) and southern (Gondwana) land masses
About 65 mya S. America split from Africa; India moved north; Australia split from Antarctica; Laurasia split into N. America and Eurasia
The final split occurred in the Cenozoic era between North America and Eurasia, which led to present distribution of continents

23. Phylogeny and Fossils Together
Phylogeny makes use of living organisms, while the fossil record supplies absolute dates and environmental context. Data from phylogeny and fossils are often used together and show strong evidence for evolution.
Phylogeny and fossils provide independent and
corroborating evidence of evolution.

24. Concept 23.2: The rise and fall of groups of organisms reflect differences in speciation and extinction rates
The history of life on Earth has seen the rise and fall of many groups of organisms
The rise and fall of groups depend on speciation and extinction rates within the group
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25. † Lineage A † † † † Common ancestor of lineages A and B Lineage B † 4
Figure 23.6 †
Lineage A † † † †
Common
ancestor of
lineages A
and B
Lineage B †
Figure 23.6 How speciation and extinction affect diversity 4 3 2 1
Millions of years ago
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26. Mass Extinctions The history of life is characterized
by rare mass extinctions.
There have been 5 major mass extinctions over the past 500 my, including:
Permian Extinction:
250 mya
Eliminated >90% marine life
Cretaceous Extinction:
65 mya
Dinosaurs became extinct
Impact Hypothesis: an asteroid or comet struck Earth while extinction was already in progress
Rare mass extinctions have altered the course of evolution. Extinctions eliminate many previously important groups of species, but they open up new possibilities for evolution.
The mass extinction at the end of the Cretaceous Period eliminated dinosaurs (except birds) and made way for the age of mammals. The most devastating mass extinction occurred 252 million years ago, at the end of the Permian Period. More than 90% of all genera recorded in late Permian oceans disappeared. Afterward, new populations of mollusks, new forms of coral, and other animals we see today rose to prominence.

27. The “Big Five” Mass Extinction Events
Figure 23.11
The “Big Five” Mass Extinction Events
1,100 25
1,000
900
Number of extant families:
(families per million years):
Total extinction rate 20
800
700 15
600
500 10
400
300 5
200
Figure Mass extinction and the diversity of life
100
Era
Period
Paleozoic
Mesozoic
Cenozoic Q C O S D C P Tr J C P N
541
359
201
145 66
In each of the five mass extinction events, 50% or more of marine species became extinct
Time (mya)
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28. 50 Predator genera (%) 40 Permian mass extinction Cretaceous
Figure 23.14 50
Predator genera (%) 40
Permian mass
extinction
Cretaceous
mass extinction 30 20 10
Figure Mass extinctions and ecology
Era
Period
Paleozoic
Mesozoic
Cenozoic C O S D C P Tr J C P N
541
359
299
252
201
145 66 Q
Time (mya)
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29. Caused the extinction of about 96% of marine animal species
The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras 252 mya
Caused the extinction of about 96% of marine animal species
A number of factors might have contributed to the Permian mass extinction
Intense volcanism in what is now Siberia
Global warming resulting from the emission of large amounts of CO2 from the volcanoes
Ocean acidification reducing the availability of calcium carbonate (CaCO3) for reef and shell building organisms
Reduced oxygen and a corresponding increase in hydrogen sulfide (H2S) producing anaerobic bacteria
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30. The Cretaceous mass extinction 66 mya :separates the Mesozoic from the Cenozoic
More than 50% of all marine species went extinct, as well as many terrestrial plants and animals, including most dinosaurs
The presence of iridium in sedimentary rocks suggests a meteorite impact about 66 million years ago
Dust clouds caused by the impact would have blocked sunlight and disturbed global climate
The Chicxulub crater off the coast of Mexico is evidence of a meteorite collision that dates to the same time
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31. Figure 23.12 Trauma for Cretaceous life
NORTH
AMERICA
Chicxulub
crater
Yucatán
Peninsula
Figure Trauma for Cretaceous life
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32. Is a Sixth Mass Extinction Under Way?
Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate
Extinction rates tend to increase when global temperatures increase
Data suggest that a sixth, human-caused mass extinction is likely to occur unless dramatic action is taken
2014 Book by Elizabeth Kolbert called The Sixth Extinction
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33. Relative extinction rate of marine animal genera 2
Figure 23.13 3
Mass extinctions
Relative extinction rate of
marine animal genera 2 1
Figure Fossil extinctions and temperature -1 -2 -3 -2 -1 1 2 3 4
Cooler
Warmer
Relative temperature
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34. Consequences of Mass Extinctions
Mass extinction can alter ecological communities and the niches available to organisms
It can take 5–100 million years for diversity to recover following a mass extinction
The type of organisms residing in a community can change with mass extinction
For example, the percentage of marine predators increased after the Permian and Cretaceous mass extinctions
Mass extinction can pave the way for adaptive radiations
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35. Adaptive Radiation
Adaptive radiation: the evolution of many diversely adapted species from a common ancestor (“spreading out”)
Adaptive radiations may follow
Mass extinctions
The evolution of novel characteristics
The colonization of new regions
Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs
The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size
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36. Adaptive Radiation in Mammals
Figure 23.15
Adaptive Radiation in Mammals
Ancestral
mammal
Monotremes
(5 species)
ANCESTRAL
CYNODONT
Marsupials
(324
species)
Eutherians
(5,010
species)
Figure Adaptive radiation of mammals
250
200
150
100 50
Time (millions of years ago)
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37. Adaptive Radiation The tarweed Carlquistia muirii Dubautia laxa
Figure 23.16
The tarweed
Carlquistia muirii
KAUAI
5.1
million
years
MOLOKAI
1.3
million
years
Dubautia laxa
OAHU
3.7
million
years
Argyroxiphium
sandwicense
LANAI
MAUI N
HAWAII
0.4
million
years
Figure Adaptive radiation on the Hawaiian Islands
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Adaptive Radiation
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38. Concept 23.3: Major changes in body form can result from changes in the sequences and regulation of developmental genes
Heterochrony is an evolutionary change in the rate or timing of developmental events
It can have a significant impact on body shape
For example, the contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates
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39. Heterochrony Chimpanzee infant Chimpanzee adult Chimpanzee fetus
Figure 23.17
Heterochrony
Chimpanzee infant
Chimpanzee adult
Figure Relative skull growth rates
Chimpanzee fetus
Chimpanzee adult
Human fetus
Human adult
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40. Heterochrony
Another example of heterochrony can be seen in the skeletal structure of bat wings, which resulted from increased growth rates of the finger bones
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41. Figure 23.19
Paedomorphosis: adults of some species keep features that were juvenile in ancestors
Gills
Figure Paedomorphosis
Axolotl—an aquatic species that becomes a sexually mature adults while keeping tadpole characteristics (gills)
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42. Changes in Spatial Pattern
Substantial evolutionary change can also result from alterations in genes that control the spatial organization of body parts
Homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged
Called Hox genes
Hox genes are a class of homeotic genes that provide positional information during animal development
If Hox genes are expressed in the wrong location, body parts can be produced in the wrong location
For example, in crustaceans, a swimming appendage can be produced in place of a feeding appendage
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43. Concept 23.4: Evolution is not goal oriented
Evolution is like tinkering—it is a process in which new forms arise by the slight modification of existing forms
Most novel biological structures evolve in many stages from previously existing structures
For example, complex eyes have evolved from simple photosensitive cells independently many times
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44. Exaptations
Exaptations are structures that evolve in one context but become borrowed for a different function
Bats’ wings evolved fro flight; but they can now use it to walk
The concept of exaptation does not imply that structures evolve in anticipation of future use
Natural selection can only improve a structure in the context of its current utility
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