Which of the following characters is absent in all chordates except mammals ?

Options

A. Sternum
B. Coelom
C. Mammary glands
D. Dorsal nerve cord

Explanation

To solve the question "Which of the following characters is absent in all chordates except mammals?", we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Phylum**: Understand that chordates belong to the phylum Chordata, which includes all animals that have a notochord at some stage of their life cycle.

2. **List the Options**: The options given are:
- A) Sternum
- B) Vertebral column
- C) Mammary glands
- D) Dorsal nerve cord

3. **Analyze Each Option**:
- **Sternum**: This is a bone found in many vertebrates, including birds and reptiles, so it is not exclusive to mammals.
- **Vertebral column**: This is present in all vertebrates, including fish, birds, reptiles, and mammals.
- **Mammary glands**: These are specialized glands that produce milk, and they are unique to mammals. Other chordates do not possess mammary glands.
- **Dorsal nerve cord**: This is a characteristic feature of all chordates, including fish, birds, reptiles, and mammals.

4. **Determine the Correct Answer**: Since mammary glands are the only feature that is absent in all chordates except mammals, the correct answer is **C) Mammary glands**.

### Final Answer:
The character that is absent in all chordates except mammals is **Mammary glands**.

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