Lesson 18

18

The Permian Period

How did some reptiles start developing features that would one day lead to mammals?

The Permian world included diverse land animals, among them synapsids on the evolutionary branch leading to mammals. Shared traits and fossils help explain how these animals are classified and how mammalian features developed over time.

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Key Ideas

  • The Permian Period lasted from about 299 to 252 million years ago, the final chapter of the Paleozoic Era.
  • Synapsids (mammal-like reptiles) dominated the land, with traits like differentiated teeth, upright posture, and evidence of warm-bloodedness.
  • The most advanced synapsids were the therapsids and cynodonts. They are the direct ancestors of every mammal alive today, including us.
  • Scientists classify animals using shared traits. Vertebrates have backbones; invertebrates do not. The fossil record tells us this story in rock layers.
  • The Permian Period was coming to a catastrophic end. The stage is set for the worst extinction in Earth's history.

Spines

Vocabulary

  • Synapsid: A group of vertebrates (including early mammal-like reptiles and eventually mammals) with a specific skull opening behind the eye.
  • Therapsid: Advanced mammal-like reptiles of the Permian and Triassic periods; direct ancestors of mammals.
  • Scales: Thin, overlapping plates covering the skin of reptiles, providing protection and waterproofing.
  • Warm-Blooded: Describes animals that regulate their own body temperature internally, regardless of the outside environment.
  • Cold-Blooded: Describes animals that rely on external heat sources to regulate body temperature; most reptiles are cold-blooded.
  • Permian: The final period of the Paleozoic Era (about 299-252 million years ago), ending in the worst mass extinction in history.
  • Fossil Record: The collection of all known fossils and their placement in rock layers, used to trace the history of life on Earth.

Discussion Questions

  1. Why do scientists group animals by body traits?
    Sample Answer: To understand how animals are alike and different.
  2. Why was having a backbone helpful for animals living on land?
    Sample Answer: It helps support body weight and allows stronger movement.
  3. If therapsids were already becoming warm-blooded, why did most of them go extinct?
    Sample Answer: Warm-bloodedness helps against temperature changes, but the Great Dying brought conditions so extreme that no single adaptation could protect against everything.
  4. How can studying Permian animals help scientists understand life today?
    Sample Answer: It shows how body plans evolved and persisted over time.

Digging Deeper

  1. Synapsids developed differentiated teeth, warm-bloodedness, and possibly fur. They are all traits carried through to modern mammals. Research one modern mammal and trace its body traits back to their Permian origins. What features connect a modern dog, bat, or whale to a Permian therapsid?
    Sample Answer: Answers will vary.
  2. Three bones that were part of the jaw in reptiles became the hammer, anvil, and stirrup in your inner ear. Research the therapsid-to-mammal jaw transition and find images showing how the bones shifted. This is one of the most well-documented evolutionary transitions in the fossil record.
    Sample Answer: Answers will vary.
  3. Build two creatures from playdough, one without a pipe cleaner inside, one with. Stack small coins or washers on each and count how many each can support before collapsing. What does this tell you about the advantage of having an internal skeleton?
    Sample Answer: The creature with the pipe cleaner inside should support more weight, which shows the advantage of an internal skeleton.