Prototheria have evolved from

Options

A. metatheria
B. reptiles
C. snakes
D. birds

Answer

### Step-by-Step Solution:

1. **Understanding Prototheria**:
- Prototheria refers to a group of egg-laying mammals, primarily consisting of monotremes, which include species like the platypus and echidna.
- They are unique among mammals because they lay eggs instead of giving birth to live young.

2. **Characteristics of Prototheria**:
- Prototheria share certain skeletal features with reptiles, indicating a close evolutionary relationship.
- Their legs are positioned on the sides of their bodies, similar to reptiles, which contributes to a reptilian gait.

3. **Evolutionary Origin**:
- Due to their reptilian-like skeletal structure and body plan, it is inferred that Prototheria evolved from reptiles.
- This evolutionary link is significant as it highlights the transition from reptilian ancestors to the development of egg-laying mammals.

4. **Analyzing the Options**:
- **Metatheria**: This group includes marsupials, which are not the ancestors of Prototheria. Therefore, this option is incorrect.
- **Reptiles**: This is the correct answer as Prototheria evolved from reptiles.
- **Snakes**: While snakes are reptiles, they are not the specific ancestors of Prototheria. This option is incorrect.
- **Birds**: Birds are a separate class of animals and do not relate directly to the evolution of Prototheria. This option is also incorrect.

5. **Conclusion**:
- Based on the analysis, the correct answer is that Prototheria have evolved from reptiles.