Lecture Notes: Dinosaur Climate and Extinction in the Mesozoic

Mesozoic Climate

• General Climate:

  • The Mesozoic era was characterized by warm, elevated temperatures often described as a greenhouse world.
  • Little to no ice at the poles.
  • Geological clues such as coal, evaporites, tillites, and glacial drop stones indicate a generally warm, ice-free world.
  • Ocean sediments suggest warmer ocean temperatures compared to the Paleozoic and Cenozoic eras.

• Variability:

  • Cooler periods were present, particularly in the early Jurassic and at the Jurassic-Cretaceous boundary.

Dinosaur Habitats and Distribution

• Early Dinosaur Sites:

  • Found in temperate forests, not the hottest tropical regions during the Triassic.
  • Fossils from the Late Triassic show dinosaurs outside tropical zones, primarily in temperate regions.
  • Few finds in tropical areas are mostly small carnivores.

• Sedimentological Evidence:

  • Found in high northern latitudes (71 degrees north) suggesting cooler winters than expected.
  • Ice-rafted debris indicates possible seasonal ice.

Climate Impact on Dinosaurs

• Impact of Seasonal Ice:

  • Sediment analysis shows similar grain sizes to modern cold regions.
  • Dinosaurs likely experienced cold winters and needed physiological adaptations to survive.

• Geochemical Data:

  • Early Jurassic says to have had possible Ice House conditions.
  • Evidence of continental ice formation during this period.

Mass Extinction Events

• End-Triassic Extinction:

  • Major extinction event affecting kuritarsi more than ave metatarsalia.
  • Dinosaurs were less affected, particularly those at middle to high latitudes.
  • Extinctions were higher in tropical-restricted taxa, suggesting a link to global cooling.

• CO2 Levels:

  • High CO2 concentrations (over 2000 ppm) explain the overall warm climate.
  • Sulfur aerosols from volcanism contributed to cooling despite high CO2.

Adaptations and Survival

• Adaptation to Cool Climates:

  • Mammals and ave metatarsalia had insulating features (fur, proto-feathers) aiding survival.
  • Scaled, large-bodied taxa were more affected by cooling.

• Late Jurassic Climate:

  • More temperate and seasonal environments replaced icy regions.
  • Aridity and precipitation influenced dinosaur distribution more than temperature.

Evolutionary Implications

• Adaptive Advantage:

  • Dinosaurs’ insulation and possible temperature regulation gave them an edge over other diapsids.
  • Expansion into new ecological roles post-extinction events.

• Future Discussions:

  • Upcoming topics will cover dinosaur physiology, potentially supporting hypotheses about their adaptability and ecological success.