Permian

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Permian

• Most notable event of the Permian is the mass
  extinction event at the end of the Permian
• This event was the largest mass extinction in
  earths history
• 90 of marine species and 70 of terrestrial
  vertebrates went extinct in just 1-8 million years

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Permian mass extinction
Trilobites
Rugosan corals
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Causes of the Permian mass extinction

• No one is sure.
• Three hypotheses have been proposed
• Asteroid impact
• Terrestrial volcanism
• Stagnant seas degassing carbon dioxide

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Cotylosaur
Stem Reptiles
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Therapsida
Mammal-like Reptiles
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Thecodontia
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Pterosauria
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Hadrosaurs (ornithiscians)
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Fig. 20.03
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Theropod dinosaur
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Deinonychus (theropod)
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Plesiosaurs
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Ichthyosaurs
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Icthyosaurs
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Fig. 20.04b
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Cretaceous plants

• Arrival of the angiosperms changed earth
  fundamentally
• During the early Cretaceous, gymnosperms were
  dominant
• The angiosperms appeared in the late Cretacous -
  100-110 mybp

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Angiosperm radiation

• By the end of the Cretaceous, 50 of the 500
  modern families had arisen

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Cretaceous insect radiation

• New groups evolved including the moths,
  butterflies, ants and bees
• Are these evolutionary arrivals unrelated to the
  radiation of angiosperms?
• I think not!
• These insects fed on nectar from the flowers
• Coevolved system - the insects relied on the
  plants for nectar and the plants relied on the
  insects for pollination

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Fig. 20.06
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Chicxulub crater

• Chicxulub crater on Mexico's Yucatan Peninsula
• 125 miles across
• Many paleontologists believe this crater is the
  site of the bolide impact that caused the K/T
  mass extinction
• Iridium signature around world

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Mammals - victors by default

• Mesozoic were midnight ramblers
• Mesozoic mammals were poor competitors with
  dinosaurs
• Radiation of mammals occurred only after the
  demise of the dinosaurs

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Tertiary mammals

• All mammals that passed through the K/T boundary
  were small and insectivorous
• Required several million years before even
  moderately sized mammals appeared
• About 10 my after the K/T boundary, some
  specialized mammals appeared
• Bats
• Whales
• Manatees

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Mesonychid
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Andrewsarchus
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Ambulocetus
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Whale evolution
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Hominid evolution

• At least nine species of hominids existed within
  the past 4 my
• Species have overlapped in space and in time
• Ancestor-descendant relationships are not clear

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Australopithecus
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Homo habilis
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• Out of Africa model
• Homo erectus spread into several populations
  across Eurasia from Africa
• Only one continent where Homo sapiens evolved,
  and that was Africa
• Modern characteristics developed first and were
  then carried out of Africa

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Fig. 21.15
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Support for Out of Africa model

• Oldest known fossil from Ethiopia - 130,000 years
  old
• Oldest fossil known outside of Africa and the
  Middle East is 40,000 years old
• Implication that H. sapiens evolved in Africa and
  migrated to Europe and Asia