Long before dinosaurs became the dominant land animals, Earth was ruled by very different ecosystems. The late Paleozoic world included giant amphibians, sail-backed synapsids, early reptiles, and forests of seed ferns and conifers. These organisms lived through dramatic climate shifts as the supercontinent Pangaea formed.
Understanding what came before dinosaurs helps explain why the first dinosaurs appeared when they did.
Key Facts
- The Permian Period lasted from about 299 million years ago to 252 million years ago.
- The Triassic Period lasted from about 252 million years ago to 201 million years ago.
- The Permian-Triassic extinction eliminated about 90% of marine species and about 70% of land vertebrate species.
- Pangaea was a supercontinent that made many inland regions hot, dry, and strongly seasonal.
- Early dinosaurs appeared in the Late Triassic, roughly 230 million years ago.
- Relative age can be estimated with superposition: in undisturbed rock layers, lower layers are older than higher layers.
Vocabulary
- Synapsid
- A vertebrate group that includes mammals and their extinct relatives, many of which were common before dinosaurs.
- Archosaur
- A reptile group that includes crocodilians, pterosaurs, dinosaurs, and birds.
- Mass extinction
- A rapid global loss of many species across different environments.
- Pangaea
- A supercontinent that joined most of Earth's landmasses during the late Paleozoic and early Mesozoic eras.
- Fossil succession
- The pattern that fossil species appear and disappear in a consistent order through rock layers.
Common Mistakes to Avoid
- Calling all prehistoric reptiles dinosaurs is wrong because dinosaurs were one branch of archosaurs, not every ancient reptile.
- Thinking dinosaurs lived during the Permian is wrong because the first known dinosaurs appeared later, in the Triassic Period.
- Assuming the Permian-Triassic extinction killed every species is wrong because many lineages survived and later diversified.
- Reading a fossil layer as younger just because it contains simpler organisms is wrong because rock position, dating evidence, and fossil succession must be used together.
Practice Questions
- 1 The Permian Period began about 299 million years ago and ended about 252 million years ago. How long did the Permian Period last?
- 2 If the first dinosaurs appeared about 230 million years ago and the Permian-Triassic extinction occurred about 252 million years ago, how many million years after the extinction did the first dinosaurs appear?
- 3 A rock outcrop contains lower layers with Permian synapsid fossils, a middle layer with extinction evidence, and upper layers with early Triassic archosaur fossils. Explain what this sequence suggests about ecological change before dinosaurs became common.