The Permian (297-251 mya)
o During the Permian period, the continents united to form the supercontinent Pangaea
o Massive volcanic eruptions: ash blocked sunlight and cooled the climate => largest glaciers
in Earth’s history.
o By the end, reptiles greatly outnumbered amphibians.
o The lineage leading to mammals diverged from one line of reptiles. Bony fishes radiated in
o Mass extinction at end: 96% species lost (volcanoes, meteorite & ocean turnover implicated)
o At the end of the Permian, a large meteorite crashed into northwestern Australia.
o Volcanic eruptions poured lava into the oceans, which depl2ted O in deep oceans. Oceanic
turnover then carried the depleted water to the surface where it released2toxic2CO and H S.
o O2concentrations dropped to about 12 percent—most animals would have been unable to
survive at elevations above 500 m.
o About 96% of all species on Earth became extinct.
Mesozoic Era (251–65 mya)
o At the start of the Mesozoic era (248 mya), the few surviving organisms found themselves in
a relatively empty world.
o Pangaea slowly separated, glaciers melted, and shallow inland seas formed.
o Life proliferated and diversified.
o Earth’s biota diversified and became distinct on each continent (previously more
Earth’s biota became increasingly provincialized: that is distinct terrestrial biotas
evolved on each continent
o By end of the era, the continents were close to their present positions and many organisms
looked similar to those living today
o Divided into The Triassic, The Jurassic, and The Cretaceous
The Triassic (251-200 mya)
o Pangaea began to break apart
o Vertebrate & invert. lineages became more diverse.
o Conifers and seed ferns became the dominant trees.
o Frogs and turtles appeared.
o Rise of reptiles, which gave rise to dinosaurs, crocodilians, and birds.
o Mass extinction at end: 65% of the species lost.
o A mass extinction at the end linked to a meteorite impact in present-day Quebec.
The Jurassic (200-145 mya)
o Two large continents: Laurasia (Laurentia (= NA) + Eurasia) & Gondwana (after region in
India, contained India + all southern continents).
o Ray-finned fishes began the great radiation that culminated in their dominance of the
o Salamanders and lizards first appeared.
o Flying reptiles! (pterosaurs)
o Dinos: bipedal predators and quadrupedal herbivores.
o Mammals first appeared.
o Plant evolution continued with the emergence of the flowering plants that dominate Earth’s
vegetation today The Cretaceous (145-65 mya)
o Gondwana breaking apart, and a continuous ocean circled the tropics. Sea levels were high
& Earth was warm and humid.
o Flowering plants (angiosperms) evolved from gymnosperms. Many groups of mammals had
evolved, but most were small. First snakes!
o Mass extinction at end of Cretaceous; it was probably caused by a large meteorite colliding
o All vertebrates larger than about 25 kg in body weight, including all of the dinosaurs,
apparently became extinct as a result of this impact.
Cenozoic (65 mya)
o By the early Cenozoic era (65 mya), the continents were close to their present-day positions;
however, Australia was still a