19.3 Evolution of Life I. Fishes first vertebrates A. Small jawless fishes 1st to appear 1. ex – hagfishes and lamprey B. Jaws evolve 1. allow fish to bite and chew food instead of sucking up 2. earliest kinds had bulky, armored bodies a. replace by flexible, agile bodies – sharks and bony fishes

C. Sharks 1. Very efficient predator 2. Skeletons not bone but flexible cartilage a. makes sharks lighter and more buoyant 3. Hundreds of species evolved about 250 species survive today D. Bony fishes 1. Replaced sharks as dominate species in seas 2. Evolved gas filled bladder called swim bladder a. enables fish to change depth with little effort

II. Amphibians onto land A. Structural innovations 1. Lungs a. could absorb oxygen through skin, lungs are far more efficient 2. Limbs a. evolved from the bones in fishes fins B. Amphibians were very successful group 1. they have survived 350 million yrs outlasting the dinosaurs C. Not perfect for land living 1. must return to water to reproduce and moisten skin

III. Reptiles A. Two key adaptations 1. watertight skin – they would dehydrate away from water 2. watertight egg – can lay eggs on dry land B. For 50 million yrs there was drought reptiles better suited to survive C. Continental Drift 1. movement of Earth’s land masses to current positions

IV. Birds and Mammals A. After last extinction 65 mya any reptile bigger than dog went extinct B. The climate shifted and was no longer dry 1. birds and mammals dominate landscape C. Humans are the 1st species to do major damage to the Earth 1. Earth’s fate lies in our hands