Mountains of western North America began forming Mesozoic life •Survivors of the great Paleozoic extinction •Gymnosperms (cycads, conifers, and ginkgoes) became the dominant trees of the Mesozoic•Reptiles (first true terrestrial animals) readily adapt to the dry Mesozoic climate •Reptiles have shell-covered eggs that can be laid on the land •Dinosaurs dominate •One group of reptiles (therapods) led to the birds Two major extinction events:•Triassic – Jurassic extinction event (End Triassic): 201.3 MYA. 70% to 75% of allspecies went extinct•Cretaceous – Paleogene extinction event (End Cretaceous, K-T extinction, or K-Pg extinction): 66 MYA. 75% of species went extinct including the dinosaurs•One hypothesis is that a large asteroid or comet struck Earth •Another possibility is extensive volcanismCenozoic EraCenozoic – “New Life”65 million years ago to the presentOften called the “age of mammals”Smaller fraction of geologic time than either the Paleozoic or the Mesozoic
North America •Most of the continent was above sea level throughout the Cenozoic era•Many events of mountain building, volcanism, and earthquakes in the West •Eastern North America •Stable with abundant marine sedimentation •Eroded Appalachians were raised by isostatic adjustments •Western North America •Building of the Rocky Mountains was coming to an end •Large region is uplifted •Basin and Range Province formed •Re-elevates the Rockies •Rivers erode and form gorges (e.g., Grand Canyon and Black Canyon) •Volcanic activity is common •Fissure eruptions form the Columbia Plateau •Volcanoes form from northern California to the Canadian border •Coast Ranges form •Sierra Nevada become fault block mountains Cenozoic life •Mammals replace reptiles as the dominant class of land animals •Angiosperms (flowering plants with covered seeds) dominate the plant world •Strongly influenced the evolution of both birds and mammals •Food source for both birds and mammals •Two groups of mammals evolve after the reptilian extinctions at the close of the Mesozoic•Marsupials- young are born undeveloped and carried in the female’s pouch (e.g. kangaroos and opossums)•Placentals- bear live young, which are nourished before birth in the mother's uterus through a specialized embryonic organ called the placenta.•Mammals diversify quite rapidly and some groups become very large •e.g., Hornless rhinoceros, which stood nearly 16 feet high •Many large animals became extinct •Humans evolve •The six great extinction event is underway. This one is caused by humans
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- Fall '15
- Extinction event, Permian, Cretaceous–Tertiary extinction event, Geological history of Earth