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Tracing Evolutionary History
Chapter 15 Tracing Evolutionary History
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Are Birds Really Dinosaurs with Feathers?
For decades, evolutionary biologists debated whether birds evolved from dinosaurs Fossil Archaeopteryx supported this view Conflicting view posited birds evolving from a very different reptile group Bird-dinosaur link was supported by cladistics and corroborated in the 1990s by fossil evidence Debate continues on how birds learned to fly
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MACROEVOLUTION AND EARTH'S HISTORY
15.1 The fossil record chronicles macroevolution Macroevolution is the main event in the evolutionary history of life on Earth Documented in the fossil record The geologic record is based on the sequence of fossils Earth's history divided into three eons Within the most recent eon, eras and periods marked by mass or lesser extinctions
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Animation: The Geologic Record
Some major events in the history of life Precambrian period: oldest known fossils- prokaryotes from 3.5 billion years ago Paleozoic era: lineages that gave rise to modern life forms Mesozoic era: age of reptiles, including dinosaurs Cenozoic era: Explosive evolution of mammals, birds, and flowering plants Animation: The Geologic Record
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15.2 The actual ages of rocks and fossils mark geologic time
Radiometric dating can gauge the actual ages of fossils and the rocks in which they are found Based on the decay time of radioactive isotopes relative to other isotopes Carbon-14 for relatively young fossils Isotopes with longer half-lives for older fossils
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15.3 Continental drift has played a major role in macroevolution
Continental drift is the slow, incessant movement of Earth's crustal plates on the hot mantle World geography changes constantly
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LE 15-03a Eurasian Plate North American Plate Arabian Plate Indian
Pacific Plate African Plate Split developing South American Plate Nazca Plate Australian Plate Antarctic Plate Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events)
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Continental movements have greatly influenced the distribution of organisms around the world
Formation of Pangaea 250 million years ago altered habitats and triggered extinctions Breakup of Pangea beginning 180 million years ago created a number of separate evolutionary arenas Explains the geographical distribution of diverse life forms Examples: marsupials, lungfishes
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LE 15-03b 65 135 251 Cenozoic Millions of years ago Mesozoic Paleozoic
Cenozoic North America Eurasia 65 Africa South America India Australia Antarctica Laurasia 135 Millions of years ago Mesozoic Gondwana 251 Pangaea Paleozoic
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LE 15-03d North America Asia Europe Africa South America Australia
= Living lungfishes = Fossilized lungfishes
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Video: Galápagos Islands Overview
CONNECTION 15.4 Tectonic trauma imperils local life Plate tectonics are the forces involved in movements of Earth's crustal plates The geologic processes that result include volcanoes and earthquakes Can create devastation or opportunities for organisms The boundaries of plates are hot spots of such geologic activity Video: Galápagos Islands Overview
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LE 15-04a San Andreas Fault North American Plate San Francisco Santa Cruz Pacific Plate Los Angeles California
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15.5 Mass extinctions were followed by diversification of life-forms
Extinctions occur all the time, but extinction rates have not been steady Over the last 600 million years, at least six periods of mass extinctions have occurred, including Permian extinction (250 million years ago); claimed 96% of aquatic life Cretaceous extinction (65 million years ago); eliminated dinosaurs
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Cause of mass extinctions is unclear
Permian extinction occurred at a time of enormous volcanic explosions Cretaceous extinction may have been caused by an asteroid Mass extinctions have been followed by an explosive increase in diversity Provide surviving organisms with new environmental opportunities Example: rise of mammals after extinction of dinosaurs
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Video: Volcanic Eruption
LE 15-05 North America Chicxulub crater Yucatan Peninsula Yucatan Peninsula Video: Lava Flow Video: Volcanic Eruption
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PHYLOGENY AND SYSTEMATICS
15.6 Phylogenies are based on homologies in fossils and living organisms Phylogeny is the evolutionary history of a group of organisms Traced partly from the fossil record Also inferred from morphological and molecular homologies among living organisms May reveal common ancestry
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Not all likenesses are inherited from a common ancestor
Analogy: similarity due to convergent evolution Species from different evolutionary branches may come to resemble each other if they live in similar environments Systematics is the analytical study of diversity and phylogeny
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15.7 Systematics connects classification with evolutionary history
Systematics includes binomial designation of species and hierarchical classification A binomial gives each species a two-part name Genus (a group of related species) Species within the genus Genera are grouped into progressively more inclusive categories (taxa) Family, order, class, phylum, kingdom, domain
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LE 15-07a Felis catus Species Felis Genus Felidae Family Carnivora
Order Mammalia Class Chordata Phylum Animalia Kingdom Eukarya Domain
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A phylogenetic tree is a hypothetical hierarchy of evolutionary relationships
(domestic cat) Felis catus Mephitis mephitis (striped skunk) Lutra lutra Canis familiaris (domestic dog) (European otter) lupus (wolf) Species Genus Family Order Carnivora Mustelidae Felidae Canidae
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15.8 Cladograms are diagrams based on shared characters among species
Cladistics is concerned with the order of branching in phylogenetic lineages Each branch (clade) on a cladogram represents an ancestral species and all its descendants Each clade consists of taxa that are monophyletic (from a "single tribe")
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All the taxa on a clade share one or more homologous features
Shared derived characters: New traits unique to each lineage Shared primitive characters: Traits present in the ancestral groups Comparison of ingroup and outgroup is important in cladistics Ingroup: Group of taxa being analyzed Outgroup: Closely related to the ingroup but not a member of it
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Parsimony seeks the simplest explanation of observed data
The simplest (most parsimonious) hypothesis of relationships creates the most likely phylogenetic tree Lizards Snakes Common reptilian ancestor Birds Crocodiles
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15.9 Molecular biology is a powerful tool in systematics
Molecular systematics uses DNA and RNA to compare relatedness The closer the nucleic acid sequences between two organisms, the more likely they are to share a common ancestor Molecular trees cover long and short times based on the different rates at which different genes evolve Humans are more closely related to fungi than to plants
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LE 15-09a Polar bear Asiatic black bear American black bear Sun bear
Sloth bear Spectacled bear Giant panda Lesser panda Brown bear Raccoon Pleistocene Pliocene 10 Miocene 15 20 Millions of years ago Ursidae 25 30 Procyonidae Oligocene 35 Common ancestral carnivorans 40
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LE 15-09b Student Mushroom Tulip Common ancestor
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Computer DNA analysis can show exactly how many bases are alike in homologous regions
Some regions of DNA change at a rate consistent enough to serve as molecular clocks to date evolutionary events Comparison of entire genomes reveals interesting homologies Humans and chimpanzees are 99% identical
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LE 15-09c Human Chimpanzee Gorilla Orangutan Common ancestor
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15.10 Arranging life into kingdoms is a work in progress
Five-kingdom system All prokaryotes are in kingdom Monera Eukaryotes are grouped into four kingdoms: Protista, Plantae, Fungi, Animalia Molecular studies have found flaws in this system
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Animation: Classification Schemes
The domain system Prokaryotes are in two domains: Bacteria and Archaea All eukaryotes are in domain Eukarya All classification systems are human constructions, not facts of nature Will always be refined by new data Animation: Classification Schemes
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Monera Protista Plantae Fungi Animalia Earliest organisms Prokaryotes
LE 15-10a Monera Protista Plantae Fungi Animalia Earliest organisms Prokaryotes Eukaryotes
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LE 15-un311-1 Lizards Birds Mammals
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