In which of the following class Hollow air - filled bones ( pneumatic bones ) occurs

Options

A. Mammals
B. Reptiles
C. Urodela
D. Aves

Answer

To solve the question regarding which class of animals possesses hollow air-filled bones (pneumatic bones), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Term "Pneumatic Bones":**
- Pneumatic bones are bones that are filled with air spaces, making them lighter. This adaptation is particularly beneficial for flight.

2. **Identify the Classes of Animals:**
- The question provides several classes of animals to consider: Aves (birds), Mammals, Reptiles, and Urodela (a class of amphibians).

3. **Analyze the Adaptations for Flight:**
- Birds (Aves) have several adaptations for flight, including:
- Hollow bones to reduce weight.
- Modified forelimbs into wings.
- Air sacs that assist in respiration during flight.
- Excretion of uric acid instead of urea.

4. **Evaluate Other Classes:**
- Mammals, reptiles, and urodela do not have pneumatic bones. Instead, their bones are typically filled with bone marrow or fatty tissue, which does not provide the same lightweight structure necessary for flight.

5. **Conclude the Correct Class:**
- Based on the adaptations discussed, the class that possesses hollow air-filled bones is Aves.

### Final Answer:
The class in which hollow air-filled bones (pneumatic bones) occur is **Aves**.

---