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Mesozoic Life. Chapter 15 Part 3. Reptiles Dinos Marine Flying Today: mammals. Permian therapsids. Mammal-like reptiles in Permian More vertical legs Fur? Warm blooded?. Transition to mammals. Cynodonts Group of therapsid Late Permian/Triassic Not clearly either reptile or mammal.

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Mesozoic Life

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Mesozoic life l.jpg

Mesozoic Life

Chapter 15

Part 3


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  • Reptiles

    • Dinos

    • Marine

    • Flying

  • Today: mammals


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Permian therapsids

  • Mammal-like reptiles in Permian

  • More vertical legs

  • Fur?

  • Warm blooded?


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Transition to mammals

  • Cynodonts

  • Group of therapsid

  • Late Permian/Triassic

  • Not clearly either reptile or mammal


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Mesozoic mammals

  • Late Triassic

  • Small during Mesozoic

  • Few species


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Mesozoic mammals

  • Late Triassic

  • Small during Mesozoic

  • Few species

  • Mammal teeth

  • Reptile and mammal jaw joints


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Mesozoic mammals

  • 2 branches

  • Prototheria

    • Monotremes: egg-laying mammals


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Mesozoic mammals

  • Prototheria

    • Monotremes: egg-laying mammals

  • Platypus, echidna


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Mesozoic mammals

  • Theria

    • Marsupial and placentals


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Where dinos warm-blooded?

  • Modern mammals, birds: warm-blooded (endotherms)

  • Modern reptiles cold-blooded (ectotherms)

  • Maybe dinos were warm blooded

    • All were

    • Some were

    • Grew to be


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How to establish

  • Where they lived

    • Some dinos in polar climates


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How to establsih?

  • Bones of modern animals

  • Endotherms

    • Bones with passageways with blood vessels

    • Ectotherms have fewer passageways

  • Dinos: bones more similar to modern endotherms

  • But some ectotherms have bones like endotherms

    • Not clear from this


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How to establish?

  • Metabolic rate/food consumption

  • Enodotherms eat more with high metabolic rate

  • Endotherm predators need large prey population

  • Ectothermic predators may be 50% of population

  • Dino predators: 3-5% of population


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How to establish

  • Brain size

  • Endotherm: Large brain relative to body to maintain temp

  • Some dinos had good sized heads

    • Small-medium theropods

  • Pin heads (sauropods) more likely ectothermic


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How to establish

  • Heart construction

  • 4 chambers like living mammals/birds

  • Some reptiles with 4 chambers


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How to establish

  • Feathered dinosaurs

    • Only endotherms have hair, fur, or feathers today


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Triassic extinction

  • 23% of marine and nonmarine families gone


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Causes of Triassic extinction

  • Impact?

  • Manicougan impact crater, Canada

  • 214 Ma


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Causes of Triassic extinction

  • Volcanoes

  • SO2 and CO2 gasses

  • Massive environmental change


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Extinction of dinos

  • Cretaceous-Tertiary boundary

  • K-T boundary

  • ~65 Ma


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Gone:

Dinos

Flying reptiles

Marine reptiles

Ammonites

Rudist bivalves

Some plankton

Cause:

Impact?

Volcanic eruptions in India?

Climate change, sea level drop?

All of the above?

Extinction of dinos


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Evidence of impact

  • Clay layer rich in element iridium

  • Iridium: rare on Earth

  • High concentrations in meteorites

  • 10 km diameter meteor impacted Earth

  • Where is the impact?


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Evidence of impact

  • Yucatan Peninsula of Mexico

  • Town of Chicxulub


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Other theories

  • Age of impact vs. age of extinction?

  • Volcanic source of iridium

    • Volcanic eruptions change climate

    • Massive eruptions in India at K-T boundary


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Other theories

  • Multiple meteorites:

    • Yucatan (65 Ma) 110 km wide

    • Ukraine (65 Ma) 15 km wide

    • North Sea (60-65 Ma) 19 km wide

    • Pack of comets struck Earth?


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