Lecture: Macroevolution and Mass Extinction

1. Lecture: Macroevolution and Mass Extinction

2. Macroevolution • Macroevolution- large-scale evolutionary changes that take place over long periods of time • 6 Themes: • Adaptive radiation (divergent evolution), convergent evolution, coevolution, punctuated equilibrium (gradualism), changes in developmental genes and mass extinction

3. Adaptive Radiation • Single species evolves into several different forms that live in different ways • New niches are always filled! • Darwin’s finches • Banobos and Chimps • Divergent Evolution- isolated populations of a species evolve independently • Geographic barriers separate members of a population, or a small group leaves • Example: Brown bear and Polar bear

4. Convergent Evolution • Unrelated organisms come to resemble each other • Species with different ancestors develop similar characteristics because natural selection has made similar adaptations in response to similar environments • Example: African serval cat and South American maned wolf

5. Coevolution • Two species evolve in response to changes in each other over time • Organisms with close ecological interactions • Many flowering plants depend on certain pollinators to reproduce and their flowers must attract them • Example: Hummingbirds and fuschia flowers

6. Gradualism vs. Punctuated Equilibrium • Gradualism- new species evolve as genomes of two populations differentiate over lots of time • Small genetic changes occur slowly • Darwin’s theory • Some evidence in fossil record, but big gaps suggest… • Punctuated equilibrium- populations remain genetically stable for long periods of time, interrupted by brief periods of rapid genetic change • This could be caused by a big environmental change, increase in mutation rates, or isolation of a small population

7. Major Time Periods- Precambrian and Paleozic • Precambrian Time- 90% of Earth’s History • All life in sea • Simple Anaerobic  photosynthetic  Oxygen  Aerobic and Eukaryotes  Multicellular • Paleozoic Era- lots of marine life • Cambrian Period- 1st hard bodies and 1st representatives of most animal phyla • Ordovician and Silurian Periods- Larger animals, first vertebrates, insect, terrestrial plants • Devonian Period- More fish, first sharks, more plants, land invasion (amphibians) • Carboniferous and Permian Periods- More vertebrates, more insects, mass extinction

8. Major Time Periods- Mesozoic and Cenozoic Eras • Mesozoic Era- 180million years- dinosaurs and flowering plants • Triassic Period- First mammals • Jurassic Period- Dinosaurs, first birds • Cretaceous- reptiles, meat-eaters, mass extinction • Cenozoic Era- mammals on land, water and air • Tertiary Period- marine mammals, flowering plants and grasses, grazers, insects • Quaternary Period- ice ages, our early ancestors

9. Mass Extinction • Mass Extinction- periods where most of the species were eliminated • 99% of life that has existed on this planet is extinct • Scientists have identified 5 mass extinctions- • Permian extinction- 250 million years ago- more than 90% of the ocean animals were eliminated • Happened around same time Pangaea formed, so maybe it was from the loss of water habitats when the super-continent formed • Cretaceous extinction- 65 million years ago- most famous extinction- wiped out the dinosaurs • Most likely explanation- a meteor

10. Cladograms • Diagrams showing the evolutionary relationships among a group of organisms • We can show appearance of new traits and relationships of organisms