Geologic Timescale 2

Triassic period

248 to 206 mya

• Mesozoic era

• First archosaurs flourished

• Archosaurs - ancestors of now extinct dinosaurs, birds and crocodiles

• “Age of reptiles”

• Therapsids (ancestors of mammals), ginkgos and cycads present

• Ended with mass extinction of marine animals, reptiles and amphibians

• Happened 8th

Jurassic period

206-144 mya

• Mesozoic era

• by this period, dinosaurs were everywhere

• First birds and first flowering plants

• First frogs and first true mammals (no larger than rats)

• Had sharks, rays, first small mammals, marine reptiles, pterosaurs, apatosaurs, stegosaurs, giant reptiles

• Happened 9th

Cretaceous period

144 to 65 mya

• a period of great biological change

• Nearly 75% of species perished in a mass extinction, which opened up habitats to surviving species

  • Ended the Mesozoic era; photosynthesis was almost nonexistent for 3 years due to debris blocking sunlight

  • Dinosaurs moved in large herds

  • Flowering plants were extremely diverse

  • T-Rex present

  • Birds and pterosaurs

• Happened 10th

Paleogene period

65 to 23 mya

• Cenozoic era

• “Age of Mammals”

• Time of great adaptive radiation

• Hoofed mammals

• Happened 11th

Neogene period

23-2.58 mya

• Cenozoic period

• The continents approached their current positions (continental drift still occurs today)

• The branch of the primate tree that includes humans arose on the middle of this period

  • The human branch originated 6 mya

• Happened 12th

Quaternary period

2.58 mya to present

• Cenozoic era

• Pleistocene epoch accounts for nearly all of it

  • Pleistocene ice ages occurred

• Homo sapiens appeared 200,000 years ago in Africa; other homo species disappeared during the Pleistocene

• Happened 13th