Mesozoic Life

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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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Extinction of dinos

• Cause
• Impact?
• Volcanic eruptions in India?
• Climate change, sea level drop?
• All of the above?

• Gone
• Dinos
• Flying reptiles
• Marine reptiles
• Ammonites
• Rudist bivalves
• Some plankton

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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?