Which of the following is not a characteristic feature of mammals?

The correct option is C

They are not warm-blooded animals

The correct option is C.

The explanation for the correct option:

1. The groups of vertebrates that possess certain unique characteristic features, which make them distinct from reptiles and amphibians are mammals.
2. They come under the class Mammalia.
3. Human beings and chimpanzees are examples of mammals.
4. All mammals possess the tendency of producing internal heat, due to which they are classed as warm-blooded animals or homoiotherms.
5. The animals, which fail to monitor their internal body temperature with the change in the environment are called cold-blooded animals, like reptiles and fish.

The explanation for the incorrect options:

Option A:

1. All mammals possess a four-chambered heart.
2. The three-chambered heart is found in reptiles and amphibians.

Option B:

1. All mammals exhibit a diaphragm, which is a muscular partition between the abdominal cavity of the body and the thorax.
2. It is generally used in the process of breathing.

Option D:

1. One of the essential characteristics of mammals is that they possess fur on their bodies.
2. It is used to insulate against the cold.

Final answer: Not being warm-blooded is not a characteristic feature of mammals.