Which of the following is a connecting link between reptiles and mammals?

Options

A. Echidna
B. Dinosaurs
C. Seymouria
D. Latimeria

Explanation

To determine which of the following is a connecting link between reptiles and mammals, we need to analyze the options provided:

1. **Echidna**
2. **Secondary Dinosaur**
3. **Seymouria**
4. **Lattimeria**

### Step-by-Step Solution:

1. **Understanding the Concept of Connecting Links**:
- A connecting link is an organism that exhibits characteristics of two different groups, in this case, reptiles and mammals. It helps in understanding the evolutionary transition between these two classes.

2. **Analyzing Each Option**:
- **Echidna**: This is a monotreme, a type of egg-laying mammal. It has features that are characteristic of both reptiles (like laying eggs) and mammals (like having fur and producing milk). This makes it a strong candidate for a connecting link.
- **Secondary Dinosaur**: This term does not refer to a specific organism and is not recognized as a connecting link between reptiles and mammals.
- **Seymouria**: This is an extinct genus that shows features of both amphibians and reptiles. While it is an important transitional fossil, it is not specifically a link between reptiles and mammals.
- **Lattimeria**: This is a genus of coelacanth fish and does not serve as a connecting link between reptiles and mammals.

3. **Conclusion**:
- Based on the analysis, **Echidna** is the correct answer as it serves as a connecting link between reptiles and mammals due to its unique characteristics.

### Final Answer:
**Echidna** is the connecting link between reptiles and mammals.

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