All of these are exclussive characteristic of mammals, except

Options

A. They are homiothermous
B. Skin has scales and hairs
C. Respiration is by lungs
D. Fertilisation is internal

Answer

To solve the question, we need to analyze each of the statements provided and determine which one is not an exclusive characteristic of mammals.

1. **Homeothermous**: This term refers to organisms that can maintain a stable internal body temperature regardless of external conditions. Mammals are indeed homeothermic, meaning they can regulate their body temperature through physiological processes like shivering and sweating. This characteristic is exclusive to mammals and birds.

2. **Skin has scales and hairs**: This statement is misleading. While mammals do have hair, they do not have scales. Scales are a characteristic of reptiles and some fish. Therefore, this statement is incorrect when referring to mammals, making it the exception among the options provided.

3. **Respiration is by lungs**: This statement is true for mammals. They possess lungs as their primary organ for respiration, which is a defining characteristic of this class of animals.

4. **Fertilization is internal**: This statement is also true for mammals. In mammals, fertilization occurs inside the female's body, which is a characteristic feature of this group.

Based on the analysis above, the statement that is not an exclusive characteristic of mammals is:

**Skin has scales and hairs.**

### Step-by-Step Solution:
1. Identify the characteristics listed in the question.
2. Analyze each characteristic to determine if it applies exclusively to mammals.
3. Conclude which statement does not fit the criteria of mammalian characteristics.