1. The History of Life on Earth Chapter 25

2. Overview: Lost Worlds Past organisms were very different from those alive Fossil record shows macroevolutionary changes over large time scales – For example: – Emergence of terrestrial vertebrates – Impact of mass extinctions – Origin of flight in birds

3. Where were these fossils found?

4. Cryolophosaurus skull 500 Mya the waters surrounding Antarctica were warm and full of tropical invertebrates. The continent was covered with Forests. These Cryolophosaurus, inhabited These forests.

5. Conditions on early Earth made the origin of life possible Chemical and physical processes on early Earth produced simple cells through these stages: 1.Abiotic synthesis of small organic molecules 2. Joining of small molecules into macromolecules 3. Packaging of molecules into protocells 4. Origin of self-replicating molecules

6. Synthesis of Organic Compounds Earth and solar system formed +/- 4.6 Bya Bombardment of Earth by rocks and ice, generating heat, vaporized water Earth’s early atmosphere contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

7. Early Research 1920s – Oparin and Haldane hypothesized that early atmosphere was reducing (electron adding) 1953 – Miller & Urey showed that abiotic synthesis of organic molecules in reducing atmosphere is possible Evidence not yet convincing that early atmosphere was reducing 1 st organic compounds may have been synthesized near volcanoes or deep-sea vents Amino acids have also been found in meteorites

8. Figure 25.2 Mass of amino acids (mg) Number of amino acids 20 10 0 1953 2008 200 100 0 1953 2008 Miller & Urey, 1953 and 2008 Amino acid synthesis in a simulated volcanic eruption

9. Abiotic Synthesis of Macromolecules RNA monomers have been produced spontaneously from simple molecules Small organic molecules polymerize when concentrated on hot sand, clay, or rock

10. Protocells Replication and metabolism are key properties of life and may have appeared together Protocells may have been fluid-filled vesicles with membrane-like structure In water, lipids and other organic molecules spontaneously form vesicles with lipid bilayer Adding clay can increase rate of vesicle formation Vesicles exhibit simple reproduction & metabolism and maintain internal chemical environment

11. (a) Self-assembly Time (minutes) Precursor molecules plus montmorillonite clay Precursor molecules only Relative turbidity, an index of vesicle number 0 20  m (b) Reproduction(c) Absorption of RNA Vesicle boundary 1  m 0 0.2 0.4 40 20 60 Presence of clay increases rate of vesicle formation Can divide on their own This vesicle has absorbed clay coated with RNA

12. Self-Replicating RNA & Dawn of Natural Selection First genetic material was probably RNA, not DNA RNA molecules called ribozymes have been found to catalyze many different reactions – Ribozymes can make complementary copies of short stretches of RNA Natural selection has produced self-replicating RNA RNA molecules that were more stable or replicated more quickly would have left most descendent RNA molecules Early genetic material might have formed an “RNA world”

13. Protocells Vesicles with RNA capable of replication would have been protocells RNA could have provided template for DNA, a more stable genetic material

14. The fossil record documents the history of life Fossil record reveals changes in history of life on Earth Sedimentary rocks deposited into layers called strata; richest source of fossils

15. Dimetrodon Stromatolites Fossilized stromatolite Coccosteus cuspidatus 4.5 cm 0.5 m 2.5 cm Present Rhomaleosaurus victor Tiktaalik Hallucigenia Dickinsonia costata Tappania 1 cm 1 m 100 mya 175 200 300 375 400 500 525 565 600 1,500 3,500 270

16. Few individuals fossilized; even fewer discovered Fossil record is biased in favor of species that – Existed for a long time – Were abundant and widespread – Had hard parts Fossil discoveries can be a matter of chance or prediction – Paleontologists found Tiktaalik (early terrestrial vertebrate) by targeting sedimentary rock from specific time and environment

17. Animation: The Geologic Record Right-click slide / select “Play”

18. How Rocks and Fossils Are Dated Sedimentary strata reveal relative ages of fossils Absolute ages determined by radiometric dating “Parent” isotope decays to “daughter” isotope at constant rate Each isotope has a known half-life – time required for half of parent isotope to decay Radiocarbon dating of Carbon can be used to date fossils up to 75,000 years old For older fossils, some isotopes (ie. Uranium) can be used to date sedimentary rock layers above and below fossil

19. Accumulating “daughter” isotope Fraction of parent isotope remaining Remaining “parent” isotope Time (half-lives) 1 2 3 4 1 2 1 4 1 8 1 16

20. Origin of New Groups of Organisms Mammals belong to group of animals called tetrapods Evolution of unique mammalian features can be traced through gradual changes over time

21. OTHER TETRA- PODS Temporal fenestra Hinge † Dimetrodon † Very late (non- mammalian) cynodonts Mammals Synapsids Therapsids Cynodonts Reptiles (including dinosaurs and birds) Key to skull bones Articular Quadrate Squamosal Dentary Temporal fenestra Hinge Hinges Temporal fenestra (partial view) Early cynodont (260 mya) Very late cynodont (195 mya) Synapsid (300 mya) Therapsid (280 mya) Later cynodont (220 mya) Figure 25.6

22. Key events in life’s history Geologic record divided into Archaean, Proterozoic, and Phanerozoic eons Phanerozoic encompasses multicellular eukaryotic life – Phanerozoic divided into three eras: Paleozoic, Mesozoic, and Cenozoic – Major boundaries between geological divisions correspond to extinction events in fossil record

24. Origin of solar system and Earth Prokaryotes Atmospheric oxygen Archaean 4 3 B i l l i o n s of y e a r s a g o

25. Origin of solar system and Earth Prokaryotes Atmospheric oxygen Archaean 4 3 Proterozoic 2 Animals Multicellular eukaryotes Single-celled eukaryotes 1 B i l l i o n s of y e a r s a g o

26. Origin of solar system and Earth Prokaryotes Atmospheric oxygen Archaean 4 3 Proterozoic 2 Animals Multicellular eukaryotes Single-celled eukaryotes Colonization of land Humans Cenozoic Meso- zoic Paleozoic 1 B i l l i o n s of y e a r s a g o

27. First Single-Celled Organisms Oldest known fossils are stromatolites, rocks formed by accumulation of sedimentary layers on bacterial mats Date back 3.5 Byz Prokaryotes were Earth’s sole inhabitants from 3.5 to 2.1 Bya

28. Prokaryotes 1 2 3 4 i y ar ago i o ll o s B e s n f

29. Photosynthesis & Oxygen Revolution Most atmospheric oxygen (O 2 ) is of biological origin O 2 produced by oxygenic photosynthesis reacted with dissolved iron & precipitated out to form banded formations By ~ 2.7 Bya., O 2 began accumulating in atmosphere and rusting iron-rich terrestrial rocks “Oxygen revolution” from 2.7 to 2.3 Bya caused extinction of many prokaryotic groups Some groups survived and adapted using cellular respiration to harvest energy

30. “Oxygen revolution” Time (billions of years ago) 4 3 2 1 0 1,000 100 10 1 0.1 0.01 0.0001 Atmospheric O 2 (percent of present-day levels; log scale) 0.001

31. Atmospheric oxygen 1 2 3 4 i y ar ago i o ll o s B e s n f

32. Cyanobacteria Early rise in O 2 likely caused by ancient cyanobacteria Later increase in O 2 may have been caused by evolution of eukaryotic cells containing chloroplasts

33. First Eukaryotes Oldest fossils of eukaryotic cells date back 2.1 billion years Endosymbiont theory: mitochondria and plastids were formerly small prokaryotes living within larger host cells

34. Prokaryotic ancestors of mitochondria and plastids probably gained entry to host cell as undigested prey or internal parasites In process of becoming more interdependent, host and endosymbionts became single organism Serial endosymbiosis: mitochondria evolved before plastids through sequence of endosymbiotic events

35. Single- celled eukaryotes 1 2 3 4 i y ar ago i o ll o s B e s n f

36. Plasma membrane DNA Cytoplasm Ancestral prokaryote Nuclear envelope Nucleus Endoplasmic reticulum Serial Endosymbiosis

37. Plasma membrane DNA Cytoplasm Ancestral prokaryote Nuclear envelope Nucleus Endoplasmic reticulum Aerobic heterotrophic prokaryote Mitochondrion Ancestral heterotrophic eukaryote

38. Plasma membrane DNA Cytoplasm Ancestral prokaryote Nuclear envelope Nucleus Endoplasmic reticulum Aerobic heterotrophic prokaryote Mitochondrion Ancestral heterotrophic eukaryote Photosynthetic prokaryote Mitochondrion Plastid Ancestral photosynthetic eukaryote

39. Key evidence supporting endosymbiotic origin of mitochondria and plastids: Inner membranes similar to plasma membranes of prokaryotes Division similar in these organelles and some prokaryotes Organelles transcribe and translate their own DNA Ribosomes are more similar to prokaryotic than eukaryotic ribosomes © 2011 Pearson Education, Inc.

40. Origin of Multicellularity Evolution of eukaryotic cells allowed for greater range of unicellular forms Second wave of diversification occurred when multicellularity evolved and gave rise to algae, plants, fungi, and animals Comparisons of DNA sequences date common ancestor of multicellular eukaryotes to 1.5 Bya Oldest known fossils of multicellular eukaryotes are small algae that lived about 1.2 Bya © 2011 Pearson Education, Inc.

41. Multicellular eukaryotes 1 2 3 4 i y ar ago i o ll o s B e s n f

42. “Snowball Earth” hypothesis: periods of extreme glaciation confined life to equatorial region or deep-sea vents 750 - 580 Mya. Ediacaran biota = assemblage of larger and more diverse soft-bodied organisms that lived 575 - 535 Mya.

43. Cambrian Explosion Sudden appearance of fossils resembling modern animal phyla in Cambrian period (535 - 525 Mya) Sponges, cnidarians, molluscs appear even earlier Cambrian explosion provides 1 st evidence of predator-prey interactions DNA analyses – many animal phyla diverged before Cambrian explosion, perhaps 700 Mya. to 1 Bya. Fossils in China provide evidence of modern animal phyla tens of millions of years before Cambrian explosion Chinese fossils suggest that Cambrian explosion lasted 40 million years

44. Sponges Cnidarians Echinoderms Chordates Brachiopods Annelids Molluscs Arthropods Ediacaran Cambrian PROTEROZOICPALEOZOIC Time (millions of years ago) 6356055755455154850

45. Animals 1 2 3 4 i y ar ago i o ll o s B e s n f

46. 150  m (b) Later stage 200  m (a) Two-cell stage Proterozoic fossils that may be animal embryos (SEM).

47. The Colonization of Land Fungi, plants, & animals began to colonize land about 500 Mya Vascular tissue in plants appeared ~ 420 Mya Plants and fungi today form mutually beneficial associations and likely colonized land together Arthropods and tetrapods – most widespread and diverse land animals Tetrapods evolved from lobe-finned fishes ~ 365 Mya

48. Colonization of land 1 2 3 4 i y ar ago i o ll o s B e s n f

49. The rise and fall of groups of organisms reflect differences in speciation and extinction rates History of life on Earth has seen rise and fall of many groups of organisms Rise and fall of groups depends on speciation and extinction rates

50. Plate Tectonics At three points in time, land masses of Earth have formed a supercontinent: 1.1 Bya., 600 Mya., & 250 Mya. According to theory of plate tectonics, Earth’s crust is composed of plates floating on mantle Tectonic plates move slowly through process of continental drift Oceanic & continental plates can collide, separate, or slide past each other Interactions between plates cause formation of mountains and islands, and earthquakes

51. Crust Mantle Outer core Inner core

52. Juan de Fuca Plate North American Plate Caribbean Plate Cocos Plate Pacific Plate Nazca Plate South American Plate Eurasian Plate Philippine Plate Indian Plate African Plate Antarctic Plate Australian Plate Scotia Plate Arabian Plate Earth’s major tectonic plates.

53. Consequences of Continental Drift Formation of Pangaea ~ 250 Mya had many effects – Deepening of ocean basins – Reduction in shallow water habitat – Colder and drier climate inland Continental drift has many effects on living organisms – Continent’s climate can change as it moves – Separation of masses can lead to allopatric speciation Distribution of fossils and living groups reflects historic movement of continents – Similarity of fossils in South America and Africa consistent with idea that continents were attached

54. 65.5 135 251 Present Cenozoic North America Eurasia Africa South America India Antarctica Madagascar Australia Mesozoic Paleozoic Millions of years ago Laurasia Gondwana Pangaea

55. Mass Extinctions 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, rate of extinction has increased dramatically and caused mass extinction – Mass extinction is result of disruptive global environmental changes In each of five mass extinction events, more than 50% of Earth’s species became extinct

56. 25 20 15 10 5 0 542 488444 Era Period 416 EOS D 359299 C 251 P Tr 200 65.5 JC Mesozoic PN Cenozoic 0 0 Q 100 200 300 400 500 600 700 800 900 1,000 1,100 Total extinction rate (families per million years) : Number of families: Paleozoic 145

57. Permian Mass Extinction Defines boundary between Paleozoic and Mesozoic eras 251 Mya Mass extinction occurred in less than 5 million years and caused extinction of about 96% of marine animal species

58. Number of factors might have contributed: – Intense volcanism in what is now Siberia – Global warming resulting from emission of large amounts of CO 2 from volcanoes – Reduced temperature gradient from equator to poles – Oceanic anoxia from reduced mixing of ocean waters

59. Cretaceous Mass Extinction 65.5 Mya Separates Mesozoic from Cenozoic Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs

60. Presence of iridium in sedimentary rocks suggests a meteorite impact about 65 Mya. Dust clouds caused by impact would have blocked sunlight and disturbed global climate Chicxulub crater off coast of Mexico is evidence of a meteorite that dates to same time

61. NORTH AMERICA Yucatán Peninsula Chicxulub crater

62. Is a Sixth Mass Extinction Under Way? Scientists estimate that current rate of extinction is 100 to 1,000 times typical background rate Extinction rates tend to increase when global temperatures increase Data suggest that sixth, human-caused mass extinction is likely to occur unless dramatic action is taken

63. Mass extinctions CoolerWarmer Relative extinction rate of marine animal genera 3 2 1 0 11 22 33 22 11 0 1234 Relative temperature

64. Consequences of Mass Extinctions Mass extinction can alter ecological communities and niches available to organisms It can take from 5 - 100 million years for diversity to recover following mass extinction Percentage of marine organisms that were predators increased after Permian & Cretaceous mass extinctions Mass extinction can pave way for adaptive radiations

65. Predator genera (percentage of marine genera) 50 40 30 20 10 0 Era Period 542 488444 416 EO S D 359 299 C 251 P Tr 200 65.5 J C Mesozoic PN Cenozoic 0 Paleozoic 145 Q Cretaceous mass extinction Permian mass extinction Time (millions of years ago)

66. Adaptive Radiations Adaptive radiation = evolution of diversely adapted species from common ancestor Adaptive radiations may follow – Mass extinctions – Evolution of novel characteristics – Colonization of new regions

67. Worldwide Adaptive Radiations Mammals underwent adaptive radiation after extinction of terrestrial dinosaurs Disappearance of dinosaurs (except birds) allowed for expansion of mammals in diversity and size Other notable radiations include photosynthetic prokaryotes, large predators in Cambrian, land plants, insects, and tetrapods

68. Ancestral mammal ANCESTRAL CYNODONT 250200150100500 Time (millions of years ago) Monotremes (5 species) Marsupials (324 species) Eutherians (5,010 species)

69. Regional Adaptive Radiations Adaptive radiations can occur when organisms colonize new environments with little competition Hawaiian Islands are one of world’s great showcases of adaptive radiation

70. Close North American relative, the tarweed Carlquistia muirii KAUAI 5.1 million years OAHU 3.7 million years 1.3 million years MOLOKAI LANAI MAUI HAWAII 0.4 million years N Argyroxiphium sandwicense Dubautia laxa Dubautia scabra Dubautia linearis Dubautia waialealae

71. Major changes in body form can result from changes in developmental genes Studying genetic mechanisms of change can provide insight into large-scale evolutionary change Genes that program development control rate, timing, & spatial pattern of changes in organism’s form as it develops into adult

72. Changes in Rate and Timing Heterochrony: evolutionary change in rate or timing of developmental events Can have significant impact on body shape Contrasting shapes of human & chimpanzee skulls are result of small changes in relative growth rates

73. © 2011 Pearson Education, Inc. Animation: Allometric Growth Right-click slide / select “Play”

74. Chimpanzee infantChimpanzee adult Human adultHuman fetus Chimpanzee fetus

75. Heterochrony can alter timing of reproductive development relative to development of nonreproductive organs Paedomorphosis – rate of reproductive development accelerates compared with somatic development Sexually mature species may retain body features that were juvenile structures in ancestral species

76. Figure 25.22 Gills

77. Changes in Spatial Pattern Substantial evolutionary change can result from alterations in genes that control placement and organization of body parts Homeotic genes determine such basic features as where wings and legs will develop or how flower parts are arranged Hox genes = class of homeotic genes that provide positional information If Hox genes are expressed in wrong location, body parts can be produced in wrong location In crustaceans, swimming appendage can be produced instead of feeding appendage

79. Evolution of Development Tremendous increase in diversity during Cambrian explosion is puzzling Developmental genes may play especially important role Changes in developmental genes can result in new morphological forms

80. Changes in Genes New morphological forms likely come from gene duplication events that produce new developmental genes Possible mechanism for evolution of six-legged insects from many-legged crustacean ancestor has been demonstrated in lab experiments Specific changes in Ubx gene have been identified that can “turn off” leg development

81. Hox gene 6Hox gene 7Hox gene 8 Ubx About 400 mya Drosophila Artemia

82. Changes in Gene Regulation Changes in morphology likely result from changes in regulation of developmental genes rather than changes in sequence of developmental genes – Threespine sticklebacks in lakes have fewer spines than their marine relatives – Gene sequence remains same, but regulation of gene expression different in the two groups

83. Threespine stickleback (Gasterosteus aculeatus) Ventral spines

84. Test of Hypothesis A: Differences in the coding sequence of the Pitx1 gene? Marine stickleback embryo Close-up of mouth Close-up of ventral surface Lake stickleback embryo Test of Hypothesis B: Differences in the regulation of expression of Pitx1? Result: No Result: Yes The 283 amino acids of the Pitx1 protein are identical. Pitx1 is expressed in the ventral spine and mouth regions of developing marine sticklebacks but only in the mouth region of developing lake sticklebacks. RESULTS

85. Evolution is not goal-oriented Evolution is like tinkering— new forms arise by slight modification of existing forms 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 different function Natural selection can only improve structures in context of its current utility

86. Figure 25.26 (a) Patch of pigmented cells (b) Eyecup Pigmented cells (photoreceptors) Pigmented cells Nerve fibers Epithelium Cornea Lens Retina Optic nerve Optic nerve (c) Pinhole camera-type eye(d) Eye with primitive lens (e) Complex camera lens-type eye Epithelium Fluid-filled cavity Cellular mass (lens) Pigmented layer (retina)

87. Evolutionary Trends Extracting single evolutionary progression from fossil record can be misleading Apparent trends should be examined in broader context Species selection model suggests that differential speciation success may determine evolutionary trends Evolutionary trends do not imply intrinsic drive toward particular phenotype

88. Holocene Pleistocene Pliocene 0 5 10 Anchitherium Miocene 15 20 25 30 Oligocene Millions of years ago 35 40 50 45 55 Eocene Equus Pliohippus Merychippus Sinohippus Megahippus Hypohippus Archaeohippus Parahippus Miohippus Mesohippus Propalaeotherium Pachynolophus Palaeotherium Haplohippus Epihippus Orohippus Hyracotherium relatives Hyracotherium Key Grazers Browsers Hipparion Neohipparion Nannippus Callippus Hippidion and close relatives