Pygostyle is complex formed by fusion of

Options

A. Thoracic and lumbar vertebrae
B. Tail vertebrae
C. Skull bones
D. All the above

Answer

To answer the question "Pygostyle is complex formed by fusion of," we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Pygostyle**:
- The pygostyle is a structure found in birds that is related to their tail.

2. **Identifying the Components**:
- The pygostyle is specifically formed from the fusion of certain vertebrae.

3. **Types of Vertebrae**:
- In birds, the vertebrae can be categorized into different types: cervical (neck), thoracic (upper back), lumbar (lower back), sacral (pelvic), and caudal (tail) vertebrae.

4. **Focusing on Caudal Vertebrae**:
- The pygostyle is formed by the fusion of the last four to five caudal vertebrae, which are also known as the tail vertebrae.

5. **Evaluating the Options**:
- The options provided include:
- A) Thoracic and lumbar vertebrae
- B) Tail vertebrae
- C) Skull bones
- D) All of the above
- From our understanding, the only correct option is B) Tail vertebrae, as the pygostyle is specifically formed from the caudal vertebrae.

6. **Conclusion**:
- Therefore, the correct answer to the question is that the pygostyle is formed by the fusion of the last four to five caudal vertebrae, also referred to as tail vertebrae.

### Final Answer:
The pygostyle is formed by the fusion of the last four to five caudal vertebrae (tail vertebrae).

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