CAPF AC 2022 Q120: Geography – Biogeography & Natural Vegetation
- (a) Lower Cretaceous
- (b) Upper Cretaceous
- (c) Early Jurassic
- (d) Middle Jurassic
Answer: (a) Lower Cretaceous
Explanation
When marsupials first appeared
How to think: place the mammals on the geological time scale.
The first small mammals appeared in the Triassic and Jurassic.
The marsupial line (pouched mammals) split off later, and its oldest fossils come from the Lower (Early) Cretaceous, about 125 million years ago.
| Period | Life |
|---|---|
| Triassic | First dinosaurs and first true mammals |
| Jurassic | Age of dinosaurs; first birds |
| Lower Cretaceous | First marsupial-line mammals; first flowering plants |
| Upper Cretaceous | Dinosaurs dominate, then die out at the end |
| Cenozoic | Age of mammals |
About marsupials: the young are born tiny and grow in a pouch.
Examples are the kangaroo, koala and opossum.
Most live in Australia and the Americas.
Answer: (a) Lower Cretaceous.
Why each option is right or wrong
- (a) CORRECT. The earliest marsupial-line fossils date to the Lower Cretaceous.
- (b) Incorrect. By the Upper Cretaceous marsupials were already widespread.
- (c) Incorrect. The Early Jurassic had early mammals but not marsupials.
- (d) Incorrect. The Middle Jurassic is still before the marsupial line appears.
Key point
Mesozoic era: Triassic → Jurassic → Cretaceous. Marsupial line: Lower Cretaceous (about 125 million years ago). Flowering plants: Cretaceous. Dinosaurs died out at the end of the Cretaceous (66 million years ago). Marsupials: pouched mammals, mainly Australia.
Remember
Marsupials first appear in the Lower Cretaceous.
Common mistakes
- Placing marsupials in the Jurassic along with the first mammals.
- Thinking mammals appeared only after the dinosaurs died out.
- Mixing up Lower (earlier) and Upper (later) parts of a period.
Exam tip
Educated guess: marsupials are more advanced than the earliest mammals, so they come after the Jurassic. Between the two Cretaceous options, a first appearance belongs to the earlier half.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography, Chapter 2: The Origin and Evolution of the Earth (geological time scale)
- Z.-X. Luo and others, An Early Cretaceous tribosphenic mammal and metatherian evolution, Science (2003)