Overview
This lecture discusses the Cretaceous Period, the final era of dinosaurs, highlighting key evolutionary changes, dominant species, environmental conditions, and the mass extinction event.
The Cretaceous Period Overview
- The Cretaceous Period lasted from about 145 to 66 million years ago.
- It was the last and longest segment of the Mesozoic Era.
- Dinosaurs reached their greatest diversity during this period.
- Flowering plants (angiosperms) appeared and spread widely.
Significant Evolutionary Developments
- Hadrosaurs (duck-billed dinosaurs) and ceratopsians (horned dinosaurs) became especially abundant.
- Tyrannosaurus rex and other large theropods dominated as top predators.
- Marine reptiles like mosasaurs and flying reptiles like pterosaurs flourished.
- Birds continued to evolve from small theropods.
Cretaceous Environment
- The climate was generally warm with high sea levels.
- Large inland seas split North America and other continents.
- Lush forests and diverse plant life provided habitats for many species.
End of the Cretaceous and Dinosaur Extinction
- A massive asteroid impact occurred near present-day Yucatán Peninsula, Mexico.
- The impact caused rapid climate changes, blocking sunlight and disrupting ecosystems.
- Dinosaurs (except birds) and many other life forms went extinct about 66 million years ago.
- This event marks the boundary between the Mesozoic and Cenozoic Eras.
Key Terms & Definitions
- Cretaceous Period — The final period of the Mesozoic Era, lasting from 145 to 66 million years ago.
- Angiosperms — Flowering plants that first appeared and diversified in the Cretaceous.
- Hadrosaurs — Duck-billed herbivorous dinosaurs common in the Cretaceous.
- Ceratopsians — Horned herbivorous dinosaurs, e.g., Triceratops.
- Theropods — Carnivorous dinosaurs including Tyrannosaurus rex.
- Mass extinction — A rapid decrease in the diversity of life forms, such as at the end of the Cretaceous.
Action Items / Next Steps
- Review prior notes on the Triassic and Jurassic periods for comparison.
- Study diagrams of dinosaur evolution and Cretaceous ecosystems.
- Prepare for quiz on the causes and effects of the end-Cretaceous extinction.