Which of the following characteristics is not shared by birds and mammals

Options

A. Breathing using lungs
B. Viviparity
C. Warm blooded nature
D. Ossified endoskeleton

Answer

To determine which characteristic is not shared by birds and mammals, we will analyze each of the provided options.

### Step-by-Step Solution:

1. **Understanding the Options**:
- The options given are:
a) Breathing using lungs
b) Viviparity
c) Warm-blooded nature
d) Ossified endoskeleton

2. **Analyzing Breathing Using Lungs**:
- Both birds and mammals breathe using lungs. Birds have specialized lungs with air sacs for efficient respiration, while mammals have lungs with alveoli.
- **Conclusion**: This characteristic is shared by both.

3. **Analyzing Viviparity**:
- Viviparity refers to giving birth to live young (as in mammals). Most mammals are viviparous, meaning the embryo develops inside the mother's body.
- Birds, on the other hand, are oviparous, meaning they lay eggs. Therefore, this characteristic is not shared.
- **Conclusion**: This characteristic is not shared by birds and mammals.

4. **Analyzing Warm-blooded Nature**:
- Both birds and mammals are warm-blooded (endothermic), meaning they can regulate their body temperature regardless of the external environment.
- **Conclusion**: This characteristic is shared by both.

5. **Analyzing Ossified Endoskeleton**:
- Both birds and mammals possess an ossified (bony) endoskeleton. This structure provides support and protection for their bodies.
- **Conclusion**: This characteristic is shared by both.

6. **Final Conclusion**:
- The only characteristic that is not shared by birds and mammals is **viviparity** (option B). Birds are oviparous, while mammals are primarily viviparous.

### Answer:
The characteristic that is not shared by birds and mammals is **viviparity (option B)**.

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