Mesozoic Cenozoic notes.notebook Mesozoic & Cenozoic 251 m.y.a Present at the end of the Permian, 90% of marine organisms and more than 70% of land organisms died. because resources and space were readily available, an abundance of new life forms appeared Mesozoic Era 251 m.y.a 65.5 m.y.a the geologic era that lasted from 251 million to 65.5 million years ago; called Age of Reptiles > lizards > turtles > crocodiles > snakes > dinosaurs Pangaea broke apart causes other collisions such as those that formed Sierra Nevada in California and Andes in South America climate was warm and humid; land covered mostly by shallow seas and marshes 1
Mesozoic Cenozoic notes.notebook Triassic Period 251 m.y.a 200 m.y.a dinosaurs appear most were about 4 5 m long lush forests of cycads (cone bearing trees like palm trees) ichthyosaurs lived in oceans ammonite is index fossil first mammals (small rodents) appear Jurassic Period 200 m.y.a 146 m.y.a dinosaurs become dominant life forms > ornithischians "bird hipped" herbivores: stegosaurus flying reptiles: pterosaurs > saurischians "lizard hipped" herbivores: apatosaurus were some of largest carnivores 2
Mesozoic Cenozoic notes.notebook Cretaceous Period 146 m.y.a 65.5 m.y.a Tyrannosaurus rex: 6m tall and had huge jaws with teeth up to 15cm long ankylosaurs: armored ceratopsians (horned), hadrosaurs (duck billed) flowering plants, angiosperms, such as magnolias, willows, maples, oaks and walnuts became dominant Cretaceous Tertiary Mass Extinction no dinosaur fossils have been found in rocks that formed after the Cretaceous some scientists believe changes in environment due to moving continents and increased volcanic activity were to blame Impact hypothesis: 65 million years ago, a giant meteorite crashed into Earth raised enough dust to block the sun's rays for many years caused cooler climates, plants died and animals became extinct > dust formed a layer of iridium laden rock iridium is commonly found in meteorites very uncommon in Earth rocks 3
Mesozoic Cenozoic notes.notebook Cenozoic Era 65.5 m.y.a Present current geologic era, which began 65.5 million years ago also called Age of Mammals continents moved to present day positions huge mountain ranges such as Alps and Himalayas formed temperatures decreased during ice ages, new species adapted to life in cooler climates mammals become dominant divided into two periods: Tertiary (time before last ice age) and Quaternary (began with last ice age and includes present time) Paleocene & Eocene Epochs 65.5 m.y.a 33.9 m.y.a many small rodents evolved first primates such as tarsier which is the sole modern survivor of earlier Paleocene ancestor of horse evolved during Eocene first whales, flying squirrels and bats appeared small reptiles flourished World wide temps. dropped by about 4o C by end of Eocene 4
Mesozoic Cenozoic notes.notebook Oligocene & Miocene Epochs 33.9 m.y.a 5.3 m.y.a Indian subcontinent began to collide with Eurasian continent, causing uplifting of Himalayas climate became drier and cooler; favors grasses and cone bearing and hardwood trees most early mammals become extinct; large species of deer, pigs, horses, camels, cats and dogs flourish clams and snails continue to flourish circumpolar currents form around Antarctica late Miocene, Mediterranean Sea dries up and refills several times largest known land mammals exist (saber toothed cats) Pliocene Epoch 5.3 m.y.a 1.8 m.y.a predators evolved into modern forms (bear, dog & cat families) herbivores such as giant ground sloth flourished modern horses appear Virginia State fossil, Chesapecten jeffersonius, was from this epoch continental ice sheets begin to spread; sea level fell > Bering land bridge appears between Eurasia and North America 5
Mesozoic Cenozoic notes.notebook Pleistocene Epoch 1.8 m.y.a 0.0115 m.y.a ice sheets advanced and retreated several times; animals had characteristics allowing them to endure cold (thick fur that covered wooly mammoths and wooly rhinoceroses) giant ground sloths and dire wolves became extinct earliest modern human fossils were found in sedimentary rock of this epoch; cave paintings found suggest they were hunters Holocene Epoch 0.0115 m.y.a Present Began 11500 years ago as last glacial period ended ice sheets melted and sea level rose about 140m, coastlines took on their present shapes and Great Lakes formed 6