Tropical conditions replaced by a colder, drier climate. Amazing diversification of birds, fish, insects and flowering plants. Cenozoic, tertiary: 65-1. 8 mya, mammals that survived expanded rapidly, birds and terrestrial insects diversified, angiosperms become the dominant land plant, fish diversified, sharks become abundant, whales appeared, hominids appeared 7mya. In paleozoic: beginning cambrian 543 million, cambrian, ordovician, silurian, devonian, Carboniferous, permian: mass extinction 250 million years ago, permian mass extinction, big mass extinction end of cretaceous: dinosaurs. Major environmental changes that have occurred on earth (page 491, figure 20. 8: first nitrogen rich atmosphere, which in turn increases amount of oxygen on earth, continents drifting and coming together, volcanic eruptions, meteorites, landslides. Describe how fossils are formed and how we know how old they are (page 491-493, figure. Explain the various biases that affect our interpretation of the fossil record (table 20. 1: animals and plants large fossilize better, abundant species fossil more, paleontologist interests.