3. A distinctive characteristic of mammals that is not observed in other vertebrates is

a. internal fertilization

b. body hair

C. the presence of a cloaca

d. endothermy

e. a vertebral column

Answer:b. body hair

Explanation: Body hair, mammary gland/breast are features that makes mammals different from other animals. The presence of body hair gives warmth and protection to the animal skin which other vertebrates lacks.

Answer: B) Body hair

Explanation: The two major characteristics of mammals are presence of body hair and feeding the young ones with breast milk. All mammals have body hair which other vertebrates such as pisces, reptiles, and amphibians do not have. Also other vertebrates do not feed their young ones with milk.