| Answer | Crossword Clue |
|---|---|
| JURASSIC | Period in which the earliest birds appeared |
| TRIASSIC | Period in which dinosaurs appeared |
| CRETACEOUS | Period in which flowering plants appeared |
| ORDOVICIAN | Period in which primitive fishes appeared |
| DEVONIAN | Period in which amphibians and insects appeared |
| SILURIAN | Period in which early invertebrate land animals appeared |
