Lesson 20

20

Dinosaurs Rise: Triassic Period

How does life rebuild after the worst extinction in Earth’s history?

During the Triassic Period, ecosystems recovered from the end-Permian extinction and new groups of animals spread. Early dinosaurs, pterosaurs, crocodile relatives, and mammals lived in a world still joined by the supercontinent Pangaea.

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Key Ideas

  • The Triassic Period (252–201 mya) was the age of recovery after the Great Dying. It is the first period of the Mesozoic Era, the Age of Reptiles.
  • Archosaurs diversified into dinosaurs, pterosaurs, and eventually birds and crocodilians. Two branches: bird-line and crocodile-line.
  • The key dinosaur advantage was upright posture (legs beneath the body) making movement more efficient and enabling bipedal walking.
  • Early dinosaurs filled empty ecological niches left by the Great Dying, diversifying rapidly from fox-sized predators to large plant eaters.
  • Early mammals also appeared in the Triassic: tiny, nocturnal, and waiting. Pangaea allowed all these animals to spread across the connected landmass.

Spines

  • DK's Science as You've Never Seen it Before: N/A
  • Mammoth Science: Breathing pg. 52
  • Visual Timelines: Life on Earth pg. 56-65
  • Alternative: Kiddle Triassic

Vocabulary

  • Triassic: The first period of the Mesozoic Era (about 252-201 million years ago) when dinosaurs first appeared after the Great Dying.
  • Dinosaur: A group of reptiles that dominated land during the Mesozoic Era; characterized by an upright stance with legs beneath the body.
  • Archosaur: The group of reptiles from which dinosaurs, pterosaurs, and eventually birds and crocodilians evolved.
  • Bipedal: Walking upright on two legs; many early dinosaurs were bipedal, giving them speed and freeing their arms.
  • Niche: The role an organism plays in its ecosystem, including what it eats, where it lives, and how it interacts with other species.
  • Mesozoic Era: The 'Age of Reptiles' (252-66 million years ago), spanning the Triassic, Jurassic, and Cretaceous periods.
  • Recovery: The process by which life rebounds and diversifies after a mass extinction, filling niches left empty by extinct species.

Discussion Questions

  1. Were dinosaurs big and scary right away, or did they start small?
    Sample Answer: No, the first dinosaurs were small and fast. Eoraptor was about the size of a fox.
  2. How did dinosaurs' upright body structure help them thrive in the Triassic?
    Sample Answer: Their upright legs made movement more efficient and less tiring.
  3. How did Pangaea help dinosaurs spread so quickly across the world?
    Sample Answer: With land connected, dinosaurs could spread easily and adapt to many environments.
  4. Why didn't early mammals dominate ecosystems instead of dinosaurs?
    Sample Answer: Mammals were small and filled limited roles, often staying hidden or active at night.

Digging Deeper

  1. Research: The Ischigualasto Formation. Look up the Ischigualasto Formation (also called the Valley of the Moon) in Argentina. What other animals lived alongside Eoraptor? Why was the Triassic a pivotal time for dinosaurs? Research how long dinosaurs had been around by the time the Jurassic began.
    Sample Answer: Answers will vary.
  2. Compare and Contrast: Dinosaurs vs. Lizards. Use a Venn diagram to compare dinosaurs and lizards. Focus on leg position, posture, body temperature regulation, and evolutionary relationships. In what ways are they similar? In what ways are they very different?
    Sample Answer: Answers will vary.