Transcript Chapter 15
Chapter 15 Tracing Evolutionary History 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 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 • Some major events in the history of life – Precambrian period: oldest known fossilsprokaryotes 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 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 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 LE 15-03a Eurasian Plate North American Plate Arabian Plate Pacific Plate African Plate Nazca Plate South American Plate Indian Plate Split developing Australian Plate Antarctic Plate Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events) • 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 LE 15-03b 0 Eurasia 65 Africa South America Antarctica Laurasia 135 251 India LE 15-03d North America Asia Europe Africa South America Australia = Living lungfishes = Fossilized lungfishes 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 LE 15-04a San Andreas Fault North American Plate San Francisco Santa Cruz Pacific Plate Los Angeles California 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 • 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 LE 15-05 North America Yucatan Peninsula Chicxulub crater Yucatan Peninsula Video: Lava Flow Video: Volcanic Eruption 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 • 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 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 LE 15-07a Felis catus Species Felis Genus Felidae Family Carnivora Order Mammalia Class Chordata Phylum Animalia Kingdom Eukarya Domain • A phylogenetic tree is a hypothetical hierarchy of evolutionary relationships Species Canis Felis Mephitis Lutra Canis lupus catus mephitis lutra familiaris (domestic (striped skunk) (European (domestic dog) (wolf) cat) otter) Genus Felis Family Felidae Order Mephitis Lutra Mustelidae Carnivora Canis Canidae 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") • 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 • Parsimony seeks the simplest explanation of observed data – The simplest (most parsimonious) hypothesis of relationships creates the most likely phylogenetic tree Lizards Snakes Crocodiles Common reptilian ancestor Birds 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 LE 15-09a Brown bear Polar bear Asiatic black bear American black bear Sun bear Sloth bear Spectacled bear Giant panda Raccoon Lesser panda Pleistocene Pliocene 10 Millions of years ago 15 20 Oligocene 25 30 Ursidae Procyonidae 35 40 Common ancestral carnivorans LE 15-09b Student Mushroom Common ancestor Tulip • 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 LE 15-09c Human Chimpanzee Gorilla Common ancestor Orangutan 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 • 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 LE 15-10a Monera Protista Earliest organisms Plantae Fungi Animalia Prokaryotes Eukaryotes LE 15-un311-1 Lizards Birds Mammals