Which of the following features is common between birds and mammals ?

Options

A. Pigmented skin and bony endoskeleton
B. Pulmonary respiration and four chambered heart
C. Viviparity and 12 pairs of cranial nerves
D. Homeotherms and four - chambered heart

Answer

To solve the question of which feature is common between birds and mammals, we can follow these steps:

### Step 1: Identify the Characteristics of Birds and Mammals
- Birds and mammals are both warm-blooded (endothermic) animals.
- They maintain a constant body temperature regardless of the environment.
- Both belong to the group of vertebrates, meaning they have a backbone.

### Step 2: Analyze Their Blood Composition
- Both birds and mammals have red blood cells (erythrocytes) and white blood cells (leukocytes) in their blood.
- The red blood cells in both groups contain hemoglobin, which is essential for oxygen transport.

### Step 3: Examine Their Circulatory System
- Both birds and mammals have a four-chambered heart, which consists of two atria and two ventricles.
- This structure allows for efficient circulation of blood, which is crucial for their high metabolic rates.

### Step 4: Evaluate the Options Given
- We need to determine which of the features listed in the options is common to both birds and mammals.
- Since both groups are warm-blooded (homeotherms) and have a four-chambered heart, we can conclude that these features are shared.

### Conclusion
The common feature between birds and mammals is that they are both homeotherms (warm-blooded) and possess a four-chambered heart.

### Final Answer
**Both birds and mammals are homeotherms.**

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