which of the following is the smallest taxonomic grounp of animals having a cranium , vertabral column , ventral heart , pulmonary respiration and two pairs of limbs

Options

A. chordata
B. Gnathostomata
C. vertebrata
D. tetrapoda

Answer

To determine the smallest taxonomic group of animals that possess a cranium, vertebral column, ventral heart, pulmonary respiration, and two pairs of limbs, we can analyze the options provided based on their characteristics.

### Step-by-Step Solution:

1. **Understanding the Characteristics**:
- The group must have a **cranium** (skull).
- It must possess a **vertebral column** (backbone).
- The heart must be **ventral** (located on the underside).
- The group should exhibit **pulmonary respiration** (breathing through lungs).
- It must have **two pairs of limbs** (total of four limbs).

2. **Evaluating the Options**:
- **Caudata**: This group includes amphibians like salamanders. However, primitive caudates do not have a well-developed cranium or vertebral column. Thus, they do not meet the criteria.
- **Protocordata**: These are primitive chordates that lack a vertebral column and cranium. Therefore, they do not qualify.
- **Agnatha**: This class includes jawless fishes (like lampreys). They do have a cranium but lack limbs and a well-developed vertebral column. Hence, they do not fulfill all the requirements.
- **Vertebrata**: This class includes all vertebrates, but it also contains groups like Agnatha that do not have limbs.
- **Tetrapoda**: This group includes amphibians, reptiles, birds, and mammals. Tetrapods have a well-developed cranium, a vertebral column, a ventral heart, pulmonary respiration, and two pairs of limbs.

3. **Conclusion**:
- The only group that meets all the specified criteria is **Tetrapoda**. Therefore, the smallest taxonomic group of animals that possess a cranium, vertebral column, ventral heart, pulmonary respiration, and two pairs of limbs is **Tetrapoda**.

### Final Answer:
**Tetrapoda**