Echidna and Ornithorhynchus are the connecting links between

Options

A. Amphibians and aves
B. Mammals and amphibians
C. Reptiles and mammals
D. Reptiles and amphibians

Explanation

**Step-by-Step Solution:**

1. **Identify the Organisms**: The question refers to two specific organisms: Echidna and Ornithorhynchus (duck-billed platypus).

2. **Classify the Organisms**: Both Echidna and Ornithorhynchus belong to the class Mammalia, which is the class of animals that includes all mammals.

3. **Recognize Unique Characteristics**: Unlike most mammals that give live birth, both Echidna and Ornithorhynchus are egg-laying mammals (monotremes). This is a unique characteristic that sets them apart from other mammals.

4. **Identify Reptilian Features**: In addition to laying eggs, these organisms also exhibit certain characteristics that are typically associated with reptiles. For example, they have a cartilaginous sheath beneath the sclera of their eyeballs.

5. **Establish the Connecting Link**: Given that Echidna and Ornithorhynchus possess features of both mammals (such as fur and mammary glands) and reptiles (such as egg-laying and certain anatomical features), they serve as a connecting link between the two classes.

6. **Conclusion**: Therefore, Echidna and Ornithorhynchus are considered connecting links between reptiles and mammals.

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