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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
Mesozoic mammals • Late Triassic • Small during Mesozoic • Few species
Mesozoic mammals • Late Triassic • Small during Mesozoic • Few species • Mammal teeth • Reptile and mammal jaw joints
Mesozoic mammals • 2 branches • Prototheria • Monotremes: egg-laying mammals
Mesozoic mammals • Prototheria • Monotremes: egg-laying mammals • Platypus, echidna
Mesozoic mammals • Theria • Marsupial and placentals
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
How to establish • Where they lived • Some dinos in polar climates
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
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
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
How to establish • Heart construction • 4 chambers like living mammals/birds • Some reptiles with 4 chambers
How to establish • Feathered dinosaurs • Only endotherms have hair, fur, or feathers today
Triassic extinction • 23% of marine and nonmarine families gone
Causes of Triassic extinction • Impact? • Manicougan impact crater, Canada • 214 Ma
Causes of Triassic extinction • Volcanoes • SO2 and CO2 gasses • Massive environmental change
Extinction of dinos • Cretaceous-Tertiary boundary • K-T boundary • ~65 Ma
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
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?
Evidence of impact • Yucatan Peninsula of Mexico • Town of Chicxulub
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
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?