 Lecture: Macroevolution and Mass Extinction

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

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

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

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

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

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- 1 st hard bodies and 1 st 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

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

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

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