UPSC Prelims 2009 Q149: Science & Technology – Biology
With reference to the evolution of living organisms,
which one of the following sequences is correct?
- (a) Octopus - Dolphin - Shark
- (b) Pangolin - Tortoise - Hawk
- (c) Salamander - Python - Kangaroo
- (d) Frog - Crab - Prawn
Answer: (c) Salamander - Python - Kangaroo
Explanation
The correct evolutionary sequence
These animals represent different stages of vertebrate evolution, each belonging to a different class.
| Option | Verdict | Reason |
|---|---|---|
| (a) Octopus - Dolphin - Shark | Incorrect | This mixes an invertebrate (octopus) with vertebrates in a non-chronological order |
| (b) Pangolin - Tortoise - Hawk | Incorrect | This places a mammal (Pangolin) before a reptile (Tortoise), reversing the actual evolutionary order |
| (c) Salamander - Python - Kangaroo | Correct | This follows the correct evolutionary sequence: amphibian (Salamander) → reptile (Python) → mammal (Kangaroo) |
| (d) Frog - Crab - Prawn | Incorrect | This mixes an amphibian (Frog) with invertebrate crustaceans (Crab, Prawn), not a coherent vertebrate evolutionary sequence |
Correct evolutionary order:
| Stage | Class | Example |
|---|---|---|
| 1 | Amphibian | Salamander |
| 2 | Reptile | Python |
| 3 | Mammal | Kangaroo |
Answer: (c) Salamander - Python - Kangaroo.
Why each option is right or wrong
- (a) Incorrect. Octopus is an invertebrate, breaking the coherent vertebrate evolutionary sequence.
- (b) Incorrect. This reverses the mammal-reptile order, placing Pangolin before Tortoise.
- (c) CORRECT. Salamander (amphibian) → Python (reptile) → Kangaroo (mammal) follows the correct evolutionary order.
- (d) Incorrect. Crab and Prawn are invertebrate crustaceans, breaking the vertebrate evolutionary sequence.
Key point
The correct vertebrate evolutionary sequence is Amphibian (Salamander) → Reptile (Python) → Mammal (Kangaroo).
Remember
Correct evolutionary sequence: Salamander (amphibian) → Python (reptile) → Kangaroo (mammal).
Common mistakes
- Mixing invertebrates (octopus, crab, prawn) into what should be a vertebrate class sequence.
- Reversing the mammal-before-reptile order in option (b).
- Not knowing the broad amphibian → reptile → mammal evolutionary timeline.
Exam tip
Vertebrate evolution timeline: amphibians first, then reptiles, then mammals. Salamander-Python-Kangaroo follows this exactly.
Sources
- NCERT Class XII Biology — Evolution
- Alfred Sherwood Romer and Thomas S. Parsons — The Vertebrate Body (Saunders)