Dentition in Mammals:

Dentition in mammals is the arrangement of teeth in the jaws. Mammals have evolved different types of dentition based on their feeding habits and lifestyle.

Heterodont Dentition:

Heterodont dentition refers to the presence of different types of teeth in the jaws. Mammals with heterodont dentition have incisors, canines, premolars, and molars. These teeth are specialized for different functions such as cutting, tearing, grinding, and crushing food. Examples of mammals with heterodont dentition include humans, dogs, and cats.

Thecodont Dentition:

Thecodont dentition refers to the condition where the teeth are set in sockets in the jawbone. This type of dentition is found in reptiles and some primitive mammals. However, most mammals have a different type of dentition.

Diphyodont Dentition:

Diphyodont dentition refers to the presence of two sets of teeth in the lifetime of a mammal. The first set of teeth, called deciduous or baby teeth, are replaced by a second set of permanent teeth. This type of dentition is found in most mammals, including humans.

Conclusion:

Therefore, the correct answer is option 'D' as dentition in mammals is heterodont, diphyodont, and not thecodont.