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Broad Patterns of Evolution
Unit 4.5 Broad Patterns of Evolution 1
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Overview: Lost Worlds Past organisms were very different from those now alive 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 2
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Figure 23.1 Figure 23.1 On what continent did these dinosaurs roam? 3
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Cryolophosaurus skull
Figure 23.UN01 Figure 23.UN01 In-text figure, Cryolophosaurus skull, p. 436 Cryolophosaurus skull 4
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Concept 23.1: The fossil record documents life’s history
The fossil record reveals changes in the history of life on Earth 5
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6 100 mya Rhomaleosaurus victor 175 200 Dimetrodon 270 Tiktaalik 300
Figure 23.2 1 m 100 mya Rhomaleosaurus victor 175 0.5 m 200 Dimetrodon 270 Tiktaalik 300 4.5 cm Coccosteus cuspidatus 375 400 1 cm Hallucigenia Figure 23.2 Documenting the history of life 500 510 2.5 cm Dickinsonia costata 560 Stromatolites 600 1,500 3,500 Tappania 6
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The Fossil Record Sedimentary rocks are deposited into layers 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 7
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Few individuals have fossilized, and even fewer have been discovered
The fossil record is biased in favor of species that Existed for a long time Were abundant and widespread Had hard parts 8
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How Rocks and Fossils Are Dated
Sedimentary strata reveal the relative ages of fossils The absolute ages of fossils can be determined by radiometric dating A “parent” isotope decays to a “daughter” isotope at a constant rate Each isotope has a known half-life, the time required for half the parent isotope to decay 9
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½ ¼ ⅛ 10 Accumulating “daughter” isotope Fraction of parent
Figure 23.3 Accumulating “daughter” isotope Fraction of parent isotope remaining Figure 23.3 Radiometric dating Remaining “parent” isotope ⅛ 1 16 1 2 3 4 Time (half-lives) 10
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Radiocarbon dating can be used to date fossils up to 75,000 years old
For older fossils, some isotopes can be used to date volcanic rock layers above and below the fossil 11
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The Geologic Record The geologic record is a standard time scale dividing Earth’s history into the Hadean, Archaean, Proterozoic, and Phanerozoic eons The Phanerozoic encompasses most of the time that animals have existed on Earth The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic Major boundaries between geological divisions correspond to extinction events in the fossil record 12
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Table 23.1 Table 23.1 The geologic record 13
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Table 23.1a Table 23.1a The geologic record (part 1: Hadean eon through Paleozoic era) 14
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Table 23.1b Table 23.1b The geologic record (part 2: Mesozoic era and Cenozoic era) 15
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Stromatolites date back 3.5 billion years ago
The oldest known fossils are stromatolites, rocks formed by the accumulation of sedimentary layers on bacterial mats Stromatolites date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants for more than 1.5 billion years 16
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Early prokaryotes released oxygen into the atmosphere through the process of photosynthesis
The increase in atmospheric oxygen that began 2.4 billion years ago led to the extinction of many organisms The eukaryotes flourished in the oxygen-rich atmosphere and gave rise to multicellular organisms 17
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The Origin of New Groups of Organisms
Mammals belong to the group of animals called tetrapods The evolution of unique mammalian features can be traced through gradual changes over time 18
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19 †Dimetrodon †Very late (non- mammalian) cynodonts
Figure 23.4 Reptiles (including dinosaurs and birds) Key to skull bones Articular Dentary OTHER TETRA- PODS Quadrate Squamosal †Dimetrodon Early cynodont (260 mya) Synapsids †Very late (non- mammalian) cynodonts Temporal fenestra (partial view) Therapsids Cynodonts Mammals Hinge Synapsid (300 mya) Later cynodont (220 mya) Temporal fenestra Hinge Figure 23.4 Exploring the origin of mammals Original hinge New hinge Therapsid (280 mya) Very late cynodont (195 mya) Temporal fenestra Hinge Hinge 19
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Synapsids (300 mya) had single-pointed teeth, large temporal fenestra, and a jaw hinge between the articular and quadrate bones 20
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Therapsids (280 mya) had large dentary bones, long faces, and specialized teeth, including large canines 21
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22 Synapsid (300 mya) Therapsid (280 mya) Key to skull bones Articular
Figure 23.4b Synapsid (300 mya) Key to skull bones Articular Quadrate Dentary Temporal fenestra Squamosal Hinge Therapsid (280 mya) Figure 23.4b Exploring the origin of mammals (part 2: synapsids and therapsids) Temporal fenestra Hinge 22
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Early cynodonts (260 mya) had large dentary bones in the lower jaw, large temporal fenestra in front of the jaw hinge, and teeth with several cusps 23
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Later cynodonts (220 mya) had teeth with complex cusp patterns and an additional jaw hinge between the dentary and squamosal bones 24
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Very late cynodonts (195 mya) lost the original articular-quadrate jaw hinge
The articular and quadrate bones formed inner ear bones that functioned in transmitting sound In mammals, these bones became the hammer (malleus) and anvil (incus) bones of the ear 25
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26 Early cynodont (260 mya) Later cynodont (220 mya)
Figure 23.4c Early cynodont (260 mya) Key to skull bones Articular Temporal fenestra (partial view) Quadrate Dentary Squamosal Hinge Later cynodont (220 mya) Original hinge Figure 23.4c Exploring the origin of mammals (part 3: cynodonts) New hinge Very late cynodont (195 mya) Hinge 26
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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 27
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28 † † Lineage A † † † Common ancestor of lineages A and B Lineage B †
Figure 23.5 † † Lineage A † † † Common ancestor of lineages A and B Lineage B † Figure 23.5 How speciation and extinction affect diversity 4 3 2 1 Millions of years ago 28
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Plate Tectonics At three 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 Tectonic plates move slowly through the process of continental drift Oceanic and continental plates can separate, slide past each other, or collide Interactions between plates cause the formation of mountains and islands and earthquakes 29
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30 North American Plate Eurasian Plate Juan de Fuca Plate Caribbean
Figure 23.7 North American Plate Eurasian Plate Juan de Fuca Plate Caribbean Plate Philippine Plate Arabian Plate Indian Plate Cocos Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Figure 23.7 Earth’s major tectonic plates Scotia Plate Antarctic Plate 30
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Consequences of Continental Drift
Formation of the supercontinent Pangaea about 250 million years ago had many effects A deepening of ocean basins A reduction in shallow water habitat A colder and drier climate inland 31
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Figure 23.8 Present Collision of India with Eurasia 45 mya Cenozoic North America Eurasia Present-day continents 65.5 mya Africa South America India Madagascar Australia Antarctica Laurasia Laurasia and Gondwana landmasses 135 mya Mesozoic Gondwana Figure 23.8 The history of continental drift during the Phanerozoic eon The supercontinent Pangaea 251 mya Pangaea Paleozoic 32
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Separation of landmasses can lead to allopatric speciation
Continental drift can cause a continent’s climate to change as it moves north or south Separation of landmasses can lead to allopatric speciation For example, frog species in the subfamilies Mantellinae and Rhacophorinae began to diverge when Madagascar separated from India 33
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34 Mantellinae (Madagascar only): 100 species Rhacophorinae
Figure 23.9 Mantellinae (Madagascar only): 100 species Rhacophorinae (India/southeast Asia): 310 species 80 60 40 20 1 2 Millions of years ago (mya) 1 2 Figure 23.9 Speciation in frogs as a result of continental drift India Madagascar 88 mya 56 mya 34
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The distribution of fossils and living groups reflects the historic movement of continents
For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached 35
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Mass Extinctions The fossil record shows that most species that have ever lived are now extinct Extinction can be caused by changes to a species’ environment At times, the rate of extinction has increased dramatically and caused a mass extinction Mass extinction is the result of disruptive global environmental changes 36
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The “Big Five” Mass Extinction Events
In each of the five mass extinction events, more than 50% of Earth’s species became extinct 37
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(families per million years):
Figure 23.10 1,100 25 1,000 900 20 800 700 15 600 (families per million years): Total extinction rate Number of families: 500 10 400 300 5 200 Figure Mass extinction and the diversity of life 100 Era Period Paleozoic Mesozoic Cenozoic Q E O S D C P Tr J C P N 542 488 444 416 359 299 251 200 145 65.5 Time (mya) 38
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The Permian mass extinction defines the boundary between the Paleozoic and Mesozoic eras 251 million years ago This mass extinction occurred in less than 500,000 years and caused the extinction of about 96% of marine animal species 39
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A number of factors might have contributed to these extinctions
Intense volcanism in what is now Siberia Global warming resulting from the emission of large amounts of CO2 from the volcanoes Reduced temperature gradient from equator to poles Oceanic anoxia from reduced mixing of ocean waters 40
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The Cretaceous mass extinction 65
The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs 41
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The presence of iridium in sedimentary rocks suggests a meteorite impact about 65 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 42
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43 Figure 23.11 Trauma for Earth and its Cretaceous life Figure 23.11
NORTH AMERICA Chicxulub crater Yucatán Peninsula Figure Trauma for Earth and its Cretaceous life 43
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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 44
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Relative extinction rate of
Figure 23.12 3 Mass extinctions 2 1 Relative extinction rate of marine animal genera −1 Figure Fossil extinctions and temperature −2 −3 −2 −1 1 2 3 4 Cooler Warmer Relative temperature 45
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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 46
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47 50 Cretaceous mass extinction Permian mass extinction 40 30
Figure 23.13 50 Cretaceous mass extinction Permian mass extinction 40 30 Predator genera (%) 20 10 Era Period Paleozoic Mesozoic Cenozoic Figure Mass extinctions and ecology E O S D C P Tr J C P N 542 488 444 416 359 299 251 200 145 65.5 Q Time (mya) 47
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Adaptive Radiations Adaptive radiation is the evolution of many diversely adapted species from a common ancestor Adaptive radiations may follow Mass extinctions The evolution of novel characteristics The colonization of new regions 48
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Worldwide Adaptive Radiations
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 Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods 49
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50 Ancestral mammal Monotremes (5 species) ANCESTRAL CYNODONT
Figure 23.14 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) 50
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Regional Adaptive Radiations
Adaptive radiations can occur when organisms colonize new environments with little competition The Hawaiian Islands are one of the world’s great showcases of adaptive radiation 51
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52 Figure 23.15 Adaptive radiation on the Hawaiian Islands
Close North American relative, the tarweed Carlquistia muirii KAUAI 5.1 million years Dubautia laxa MOLOKAI 1.3 million years MAUI Argyroxiphium sandwicense OAHU 3.7 million years LANAI HAWAII 0.4 million years N Figure Adaptive radiation on the Hawaiian Islands Dubautia waialealae Dubautia scabra Dubautia linearis 52
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KAUAI 5.1 million years MOLOKAI 1.3 million OAHU years 3.7 MAUI
Figure 23.15a KAUAI 5.1 million years MOLOKAI 1.3 million years MAUI OAHU 3.7 million years LANAI HAWAII 0.4 million years Figure 23.15a Adaptive radiation on the Hawaiian Islands (part 1: map) N 53
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Concept 23.3: Major changes in body form can result from changes in the sequences and regulation of developmental genes Studying genetic mechanisms of change can provide insight into large-scale evolutionary change Genes that program development influence the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult 54
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Changes in Rate and Timing
Heterochrony is an evolutionary change in the rate or timing of developmental events It can have a significant impact on body shape The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates 55
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56 Chimpanzee infant Chimpanzee adult
Figure 23.16 Chimpanzee infant Chimpanzee adult Figure Relative skull growth rates Chimpanzee fetus Chimpanzee adult Human fetus Human adult 56
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Another example of heterochrony can be seen in the skeletal structure of bat wings, which resulted from increased growth rates of the finger bones 57
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Figure 23.17 Figure Elongated hand and finger bones in a bat wing Hand and finger bones 58
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Heterochrony can alter the timing of reproductive development relative to the development of nonreproductive organs In paedomorphosis, the rate of reproductive development accelerates compared with somatic development The sexually mature species may retain body features that were juvenile structures in an ancestral species 59
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Figure 23.18 Gills Figure Paedomorphosis 60
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Changes in Spatial Pattern
Substantial evolutionary change can also result from alterations in genes that control the placement and 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 61
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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 instead of a feeding appendage 62
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The Evolution of Development
Adaptive evolution of both new and existing genes may have played a key role in shaping the diversity of life Developmental genes may have been particularly important in this process 63
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Changes in Gene Sequence
New morphological forms likely come from gene duplication events that produce new developmental genes A possible mechanism for the evolution of six-legged insects from a many-legged crustacean ancestor has been demonstrated in lab experiments Specific changes in the Ubx gene have been identified that can “turn off” leg development 64
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65 Hox gene 6 Hox gene 7 Hox gene 8 Ubx About 400 mya
Figure 23.19 Hox gene 6 Hox gene 7 Hox gene 8 Ubx About 400 mya Figure Origin of the insect body plan Drosophila Artemia 65
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Changes in Gene Regulation
Changes in morphology likely result from changes in the regulation of developmental genes rather than changes in the sequence of developmental genes For example, threespine sticklebacks in lakes have fewer spines than their marine relatives The gene sequence remains the same, but the regulation of gene expression is different in the two groups of fish 66
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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 67
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Evolutionary Novelties
Most novel biological structures evolve in many stages from previously existing structures Complex eyes have evolved from simple photosensitive cells independently many times Exaptations are structures that evolve in one context but become co-opted for a different function Natural selection can only improve a structure in the context of its current utility 68
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69 Figure 23.21 A range of eye complexity in molluscs
(a) Patch of pigmented cells (b) Eyecup Pigmented cells (photoreceptors) Pigmented cells Epithelium Nerve fibers Nerve fibers Example: Pleurotomaria, a slit shell mollusc Example: Patella, a limpet (c) Pinhole camera-type eye (d) Eye with primitive lens (e) Complex camera lens- type eye Epithelium Cellular mass (lens) Cornea Fluid-filled cavity Cornea Figure A range of eye complexity in molluscs Lens Retina Optic nerve Optic nerve Optic nerve Pigmented layer (retina) Example: Murex, a marine snail Example: Nautilus Example: Loligo, a squid 69
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Evolutionary Trends Extracting a single evolutionary progression from the fossil record can be misleading Apparent trends should be examined in a broader context The species selection model suggests that differential speciation success may determine evolutionary trends Evolutionary trends do not imply an intrinsic drive toward a particular phenotype 70
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