Which one of the following characters is not typical of the class-mammalia?

The character that is not typical of the class Mammalia is alveolar lungs. Mammals have a different type of lung structure, which is characterized by the presence of alveoli, but they are not the only animals to have this type of lung structure. However, the other options are all typical characteristics of mammals. Mammals have seven cervical vertebrae, thecodont dentition, and ten pairs of cranial nerves. So, the correct answer is option D. Notice that the other options are correct. Mammals do have seven cervical vertebrae, thecodont dentition, and ten pairs of cranial nerves.