Lesson 22

22

Cretaceous Life & Flowering Plants

How did flowers change the world for every living thing?

Flowering plants spread during the Cretaceous Period alongside diverse dinosaurs and other animals. Pollination, fruits, and seed dispersal show how relationships between plants and animals changed ecosystems.

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Key Ideas

  • The Cretaceous Period (145–66 mya) had the greatest diversity of dinosaurs in history, continental separation drove populations to evolve in different directions.
  • Flowering plants (angiosperms) appeared and spread rapidly, outcompeting older plant groups through reliable animal-assisted pollination and seed dispersal via fruits.
  • Coevolution shaped flowers and their pollinators together: flowers became more elaborate; insects evolved specialized tools to access nectar; both benefited.
  • The Cretaceous world was the most complex and interconnected ever produced: new flowers, new insects, diverse dinosaurs, and mammals still quietly waiting.
  • The Cretaceous ends with the K-Pg extinction, the subject of our next lesson, which closes the Age of Reptiles and opens the door for the mammals.

Spines

Vocabulary

  • Cretaceous: Final Mesozoic Period (145–66 mya); flowering plants appeared, dinosaurs peaked in diversity.
  • Angiosperm: A flowering plant that produces seeds in a fruit; the dominant plants on Earth today.
  • Pollinator: An animal that carries pollen between flowers, enabling plants to reproduce.
  • Coevolution: Two species shaping each other's evolution as they adapt to each other over millions of years.
  • Pollen: Tiny grains containing a plant's male reproductive cells; transported by wind or animals.
  • Deciduous: A plant that sheds its leaves seasonally; became more common during the Cretaceous.
  • Diversification: A rapid increase in the variety of species in a group; angiosperms diversified explosively.

Discussion Questions

  1. What is different about flowering plants compared to earlier plants and why did the difference matter so much?
    Sample Answer: Earlier plants scattered pollen on the wind, which wasted most of it. Flowering plants use animals to carry pollen directly to the right plant, which is targeted and efficient.
  2. What is coevolution? Give an example from this lesson.
    Sample Answer: Coevolution is two species shaping each other's evolution. For example, flowers became more elaborate as bees got better at finding them.
  3. Why might the Cretaceous be considered a turning point in Earth's ecosystems?
    Sample Answer: Flowering plants, pollinators, fruits and seed dispersal all appeared, and they are still central to modern ecosystems.
  4. What might happen if pollinators disappeared from Earth today?
    Sample Answer: About 75% of flowering plant species depend on animal pollinators, so food webs, agriculture, and wild plant communities would all be affected.

Digging Deeper

  1. Fruit Dissection: Cut open several fruits (apple, orange, tomato, bell pepper). Count the seeds in each. Look at how they are arranged. Remember: every fruit you see is a structure that evolved to make animals carry seeds for the plant. For each fruit, think about which animal it is designed for. How does the size, color, and taste of the fruit match the animal that would have spread its seeds?
    Sample Answer: Answers will vary.
  2. Darwin's Abominable Mystery: Darwin called the sudden appearance of flowering plants in the fossil record an 'abominable mystery.' It still is not fully solved. Research the leading hypotheses: rapid coevolution with insects, genome changes, or gaps in the fossil record. Write a short paragraph explaining the mystery and one possible explanation.
    Sample Answer: Answers will vary.
  3. Pollinator Watch: Spend 10 minutes near flowering plants and count how many different insects or birds visit. Record what each one does on the flower: where it lands, how long it stays, whether it seems to stay on one flower species. You are watching the Cretaceous partnership that began 100 million years ago. What do you notice?
    Sample Answer: Answers will vary.