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

Options

A. Diphyodont tooth
B. Ten pairs of cranial nerves
C. Seven cervical vertebrae
D. Left aortic arch in the circulatory system

Answer

To determine which of the following is not a characteristic feature of mammals, we will analyze each option provided.

1. **Diffused on tooth**: This option refers to the type of teeth that mammals possess. Mammals typically have differentiated teeth, including incisors, canines, premolars, and molars. In humans, for instance, milk teeth are replaced by permanent teeth, which are specialized for different functions. Therefore, this option is a characteristic feature of mammals.

2. **10 pair of cranial nerves**: This option states that mammals have 10 pairs of cranial nerves. However, mammals actually have 12 pairs of cranial nerves. This means that this option is not a characteristic feature of mammals.

3. **7 cervical vertebrae**: This option indicates that mammals possess 7 cervical vertebrae. This is indeed a characteristic feature of mammals, as all mammals, including humans, have seven cervical vertebrae in their necks.

4. **Left aortic arch in the circulatory system**: This option refers to the structure of the circulatory system in mammals. Mammals typically have a left aortic arch, which is a characteristic feature of their anatomy.

After analyzing all the options, we conclude that the correct answer is option 2: **10 pair of cranial nerves**, as mammals actually have 12 pairs of cranial nerves.