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| The Mesozoic Era (248 - 65 million years ago) Ages of the Mesozoic Era | ||||||||
| Triassic Period 248 - 206 mya First dinosaurs and mammals |
Jurassic Period 206-144 mya Many dinosaurs and the first birds |
Cretaceous Period 144-65 mya First flowering plants, the height of the dinosaurs. Ends in huge extinction. |
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| Early - Middle 248-227 mya |
Late 227-206 mya |
Early (Lias) 206-180 mya |
Middle (Dogger) 180-154 mya |
Late (Malm) 154-144 mya |
Early (Neocomian) 144-127 mya |
Middle (Gallic) 127-89 mya |
Late (Senonian) 89-65 mya |
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were flourishing, and flowering plants 
developed and radically changed the landscape.
The breakup of the supercontinent Pangaea into separate continents was underway. The separation of Laurasia and Gondwana was complete. In the first half of the Cretaceous, temperatures were warm, seasonality was low, and global sea levels were high (no polar ice!). At the end of the Cretaceous, there were severe climate changes, lowered sea levels, and high volcanic activity 
.
The Cretaceous period ended 65 million years ago with the extinction of the dinosaurs and many, many other prehistoric life forms. This mass extinction was the second-most extensive in the history of the Earth.
Creta is the Latin word for chalk. The Cretaceous period is named for chalky rock from southeastern England that was the first Cretaceous period sediment studied.
(anthophytes, also called angiosperms) continued to develop (they evolved about 140 million years ago, during the late Jurassic period). Flowering plants (like magnolia, ficus, credneria, sassafras, viburnum) quickly outnumbered the other plants (mostly ferns 
, horsetails, trees (like conifers and gingkos), and cycads 
), changing the environment tremendously. The extinction of bennettitaleans (a major group of plants) also occurred at this time.
Most of the land mass was at or around sea level until the mid-Cretaceous, a time of high tectonic activity (continental plate movement) and accompanying volcanic activity . This is when many mountain ranges were formed
, including California's Sierra Nevadas, the Rocky Mountains in the western USA and the European Alps. The sea levels rose during the mid-Cretaceous, covering about one-third of the land area. Toward the end of the Cretaceous, there was a drop in sea level, causing land exposure on all continents, more seasonality, and greater extremes between equatorial and polar temperatures. Also, the continents were taking on their modern-day forms.
, ichthyosaurs 
, ammonites, mosasaurs, plesiosaurs, and half of all invertebrate marine organisms. The primary cause of the Cretaceous-Tertiary extinction is thought to be an asteroid impact 
, but there are a lot of other theories, including high volcanism, climate changes due to continental drift, the effects of disease, and/or competition from egg-eating mammals 
. Although this extinction was huge, it was small when compared to the Permian-Triassic extinction (which preceded the existence of the dinosaurs).
Printout:
Cretaceous animal printouts
| The Mesozoic Era (248 - 65 million years ago) Ages of the Mesozoic Era | ||||||||
| Triassic Period 248 - 206 mya First dinosaurs and mammals |
Jurassic Period 206-144 mya Many dinosaurs and the first birds |
Cretaceous Period 144-65 mya First flowering plants, the height of the dinosaurs. Ends in huge extinction. |
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| Early - Middle 248-227 mya |
Late 227-206 mya |
Early (Lias) 206-180 mya |
Middle (Dogger) 180-154 mya |
Late (Malm) 154-144 mya |
Early (Neocomian) 144-127 mya |
Middle (Gallic) 127-89 mya |
Late (Senonian) 89-65 mya |
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