A history of life on earth Chapter 5 Important patterns in the history of life Climates and land masses have changed over time Taxonomic composition has changed There are periods of mass extinction High diversification, esp. after mass extinctions Diversification includes increases in number of species and variety of forms Important patterns in the history of life Extinct taxa replaced by similar but unrelated forms Ancestral members of a taxa more alike than their descendants Only a few members of higher taxa have persisted Geographic distribution has changed greatly The Big Bang Theory 12-15 billion years ago all matter and energy were concentrated into a (relatively) small space the size of our sun About ten billion years ago, the Universe began in a gigantic explosion Matter then condensed to form atoms, elements, and eventually galaxies and stars Geologic time units Geologic Time Line Eon a unit of time 1 billion years Era a unit of time marked by a new or distinct order of things Period an unit of time of any length Epoch a period that began by some significant change or event 1
Geological time Phanaerozoic time Formation of Earth Earth was formed 4.6 billion years ago by the collision and aggregation of many smaller bodies As Earth cooled, crust formed and water and other gases were released Precambrian time What is life? Self-replication Differential reproduction, with variation = genotype Metabolism Intake, processing, outflow of materials = phenotype Individuality Coherence as integrated system, subject to selection All life is related All share similar features Use only L-optical isomers of amino acids Universality of genetic code Archeon Eon 3.8 2.5 bya Chemical and molecular evolution First cells (anaerobic bacteria) 2
How did life originate? The problem The setting Simple chemicals DNA, RNA, proteins (enzymes!), membranes metabolism integrated system! Energy: lightning, volcanoes, sunlight, heat Materials: CO 2, CO, N 2, H 2 O, CH 4? NH 3? But NO oxygen! Environment: rocks, water PRIMORDIAL SOUP The Oparin-Haldane model Stanley Miller made his own soup : CH 4 + NH 3 + H 2 + ENERGY = amino acids, sugars Some controversy now over whether this adequately represented earth s atmosphere Simple organic chemicals can be made by abiotic chemical reactions Origin of agents of metabolism Going cellular Spontaneous formation of porphyrin rings from formaldehyde Components of chlorophylls and cytochromes formaldehyde Chlorophyll a Compartmentalization into individuals makes replication more efficient Lipid membranes spontaneously selfassemble porphyrin ring system 3
membrane-bound proto-cells living cells The first cells Possible sequence leading to self-replicating systems DNA self-replicating system enclosed in a selectively permeable, protective lipid sphere RNA formation of protein RNA systems, evolution of DNA enzymes and other proteins spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions formation of lipid spheres Stromatolites from 3.5 bya Were prokaryotic heterotrophs Secured energy through anaerobic pathways No oxygen present Relied on glycolysis and fermentation Origin of photosynthesis Origin of photosynthetic eubacteria Noncyclic pathway first (3.5 mya) Cyclic pathway next (2.5 bya) Oxygen accumulates in atmosphere and increases greatly 2.2 bya Origin of aerobic respiration The first cells were prokaryotes Reminder: prokaryotes are single celled organisms lacking a nuclear envelope Two of the three domains (Bacteria, Archaea) are prokaryotes Prokaryotes were only life forms for 2 billion years Prokaryotic cells Archaebacteria Live in extreme habitats Salt, extreme temperatures, anaerobic Methane-producing bacteria Bacteria Live everywhere - aerobic conditions Live on your skin, digestive systems 4
Eukarya Distinct nucleus with membrane, distinct chromosomes; majority with organelles, many multicellular Protistans Some are single cell/others are multicellular Larger than bacteria Usually live in aquatic environments Amoeba, paramecium, algae Fungi Plants Animals Emergence of eukarya Fossils from 1.5 bya Chemical evidence of emergence 2.7 bya Where did organelles come from? Theory of Endosymbiosis Free-living prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts Theory of endosymbiosis Mitochondria and chloroplasts resemble simple bacteria Sequencing of plastids from organelles suggests bacterial symbiont origin Membrane number suggests origin type Lynn Margulis Theory of endosymbiosis Some extant eucarya have no mitochondria Rely on endosymbiotic bacteria for respiration Many nuclei, each surrounded by bacteria (in Pelomyxa) Purple = cyanobacteria (in flagellate) 5
Theory of endosymbiosis Corals and algae Deep sea fish headlights Multicellularity Origin of life, 3500 mya 1500 mya eukaryotes 640 mya large multicellular animals WHY THE WAIT? Phanaerozoic Advantages of multicellularity Replacement of cells = longer life Larger organisms have greater physiological stability Cell differentiation into tissues means different sorts of body architectures (can exploit new niches) Ingest small organisms, produce more offspring Disadvantages of multicellularity Longer development means later reproduction (lower r) Larger size means problems with respiration, circulation (volume increases more rapidly than surface area) 6
Multicellularity Paleozoic Era (570-240 mya) Multicellular organisms need more oxygen than single-celled organisms Cambrian period 542-489 mya Continents were flooded by shallow seas The super continent of Gondwana just formed The Cambrian Explosion At beginning of Cambrian Period, modern animal phyla present, little in fossil record By 530 Ma, almost all modern animal phyla present in fossil record! Trilobite Opabinia Brachiopods and trilobites Burgess Shale of British Columbia 7
The Cambrian Explosion Earliest known vertebrate ancestors Teeth of cellular bone, lacked vertebrae but had notochord: conodonts Animal body plans evolved during Cambrian What caused the Cambrian Explosion? Environmental changes: increased O 2, calcium carbonate (for shells!) Ecological setting: lots of unfilled niches, available as new modes of locomotion evolved Key innovations: multicellularity, important new developmental pathways Why no replay? Similar availability of niches after end- Permian extinction! Developmental processes malleable in early metazoans, but more canalized later: can t evolve truly unique forms End of Cambrian Extinction marked the end of the Cambrian period, perhaps caused by cooling of the seas Trilobites greatly reduced Several classes of echinoderms extinct Ordovician Period 488-443 mya End of the Ordovician was one of the coldest times in Earth history 8
Marine Diversification Ordovician - Major diversification of marine organisms: more niches filled! End of Ordovician Mass extinction may have been caused by drop in temperature and drop in sea level Second largest extinction Silurian Period (444-415 mya) Gondwana drifts N Sea level rises and ice sheets melt Ammonoids Gnathostomes Marine vertebrates with jaws and fins 9
The colonization of land Silurian into Devonian Plants invaded land in the late Silurian/early Devonian, 408 Ma, probably in wet, transitional habitats Silurian Devonian Period (416-358 mya) Pangea starts to form The colonization of land Major hurdle: water loss Key innovations at this time: vascular tissue, support tissue (no water to hold up body); spores, then seeds (with protective covering), for reproduction without water First land animals Dinosaurs 10
Mosses Mosses and liverworts and liverworts (nonvascular plants) (nonvascular plants)) Lycopods (vascular plants) Horsetails (also vascular plants) Calamites (giant horsetails) The colonization of land Earliest terrestrial animals were arthropods, in Devonian, with marine ancestors Chelicerates: spiders, scorpions Mandibulates: millipedes, springtails Chelicerates predatory 11
Mandibulates Herbaceous, predatory, detritivores Colonization of land Terrestrial vertebrates arose in late Devonian Amphibians, fed on arthropods in swampy (transitional) habitats Although extant tetrapods have five (or fewer) digits, recent discoveries show that early amphibians had 7 or 8 digits Acanthostega Ichthyostega End of Devonian Mass extinction marked end of Devonian Carboniferous Period (354-290 mya) Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains Sea levels swing widely The first forests Diversification of seed ferns, gymnosperms, no flowering plants yet First winged insects, including dragonflies with 70 cm wingspans! Swamp forests of Lepidodendron and Archaeopteris created ideal habitats for fishes, amphibians 12
Coal swamps in the Carboniferous, with Sigillaria, seed ferns The Amniote Egg Amniotes include reptiles, birds, mammals; diverged late Carboniferous Derived from amphibians Amniote egg allowed terrestrial reproduction: a key innovation Amniotes Synapsids: ancestors to mammals Anapsida, Synapsida, Diapsida Refers to skull openings: none, one, or two Anapsids are turtles Synapsids are mammal-like reptiles Diapsids gave rise to lizards, archosauromorphs (crocs, dinosaurs) Dimetrodon Tetraceratops 13
Permian Period (299-250 mya) Vast deserts covered western Pangea during the Permian as reptiles spread across the face of the super continent Permian Period Insects, amphibians, and early reptiles in swamp forests PANGEA Permian extinction Largest mass extinction (96% of species) Lowest sea levels in history Ammonites, stalked echinoderms, brachiopods reduced Trilobites and many corals extinct Extinctions on land less pronounced The Mesozoic Era Divided into three periods Triassic Jurassic Cretaceous Major geologic event was the breakup of Pangea Pangea allowed land animals to migrate from the South Pole to the North Pole Life began to rediversify after the great Permian extinction and warm-water faunas spread across Tethys Sea Period of warm, mild climate Mesozoic: the age of reptiles Both marine and terrestrial forms Land plants dominated by cycads and gymnosperms Anatomically advanced insect orders, including hymenoptera 14
Triassic Period (251-199 mya) Marine reptiles: Lepidosaurs Seas repopulated after Permian extinction First dinosaurs and mammals Ichthyosaur: porpoiselike, gave birth to live young Plesiosaur The Amazing Archosaurs Pterosaurs: evolved true flight Quetzalcoatlus Wingspan 12 m The Amazing Archosaurs Ornithischia: Hadrosaurs Stegosaurs The Amazing Archosaurs Saurischia: Tyrannosaurus rex Apatosaurus The Amazing Archosaurs Birds: living archosaurs 15
Long-necked Sauropods and shorter hadrosaurs Synapsids gave rise to therapsids Cycads Ginkgo: a living fossil, an early seed plant, relationships unresolved End of Triassic Mass extinction Ammonoids and bivalves decimated Jurassic Period (200-144 mya) A wide Tethys ocean separated the northern continents from Gondwana Continents break up by end of period 16
number of genera Jurassic Period Radiation of the dinosaurs Mesozoic marine revolution Crabs Bony fishes telosts appear Gastropods, bivalves and bryozoans rose to dominance Ichthyosaur Mammals Morganudoconts Cretaceous Period (145-65 mya) More continental movement Cretaceous Period 200 angiosperms Surviving dinosaurs diversify Seedless plants and gymnosperms begin to decline Rise of Flowering Plants 150 100 ferns cycads 50 gymnosperms ginkgo Deinonuchus 0 other genera 160 140 120 100 80 60 millions of years ago 17
Radiation of the Angiosperms (125 Mya) Early angiosperms (flowering plants) were non-woody, had a competitive advantage over gymnosperms (conifers, ginkgo) Sauropods with long necks may have fed on tall conifers in Jurassic Shorter Hadrosaurs in Cretaceous may have provided selection pressure that favored rapidly growing angiosperms End of Cretaceous Mass extinction Only one surviving lineage of dinosaurs K-T Asteroid Impact Asteroid Cretaceous seaway land Length extends halfway between Baltimore and Washington, DC Present Cenozoic Era Two Periods Tertiary Period Quaternary Period Seven Epochs 18
Tertiary Period (65 mya 5 mya) More continental movement The adaptive radiation of the mammals First appeared in Triassic, placental mammals and marsupials in late Creteceous, big radiation in the Tertiary First mammals insectivorous or omnivorous; carnivory associated with diversification Homeothermy, hair, milk = shared traits; most are viviparous Mammal radiation Three subclasses: Prototheria (platypus, echidna: NOT viviparous) Mammal radiation Three subclasses: Metatheria (marsupials) Mammal radiation Three subclasses: Eutheria (placentals) Mammal radiation Sinapsids to therapsids to cynodonts to mammals 19
Mammal radiation Mammal radiation Phylogenetic relationships were difficult to resolve: radiation was fast Angiosperm coevolution with insects The flower as a key innovation Synchronicity between adaptive radiation of hymenoptera and lepidoptera, and adaptive radiation of angiosperms, in Tertiary Insect pollination more efficient than wind pollination The pollinators: bees, moths/butterflies, flies Angiosperm coevolution with insects Coevolution between plants and insect herbivores also important Resin canals, a defense, has evolved multiple times 20
The herbivores: bugs and beetles Oligocene Adaptive radiation of Poaceae Quaternary Period (5 mya-present) The world has taken on a "modern" look, but note that Florida and parts of Asia were flooded by the sea Pleistocene The last expansion of the polar ice sheets took place about 18,000 years ago Ice age Sea levels dropped 70% of mollusc species became extinct Global climate generally drier Later Cenozoic Earth in ice age Climates became cooler and drier Grasslands and woodlands dominated Grazing and browsing animals thrived 21
Extinctions in Pleistocene Shallow water marine invertebrates Large bodied mammals and birds Ground sloth Giant bison Saber tooth tiger Current extinction We are perhaps in the midst of another mass extinction Earth today 22
Earth is just right for life If Earth were smaller in diameter, gravity would not be great enough to hold on to atmosphere If Earth were closer to sun, water would have evaporated If Earth were further from sun, water would have been ice Mammal radiation Major changes over time: Cranial characters, probably for mobility and speed Jaw characters, probably for subduing prey All skeletal characters modified from those existing in ancestors 23