The biggest land mammals of all are the elephants, rhinoceroses and hippopotamuses of tropical Africa and Asia. Yet there are very few of them. The most numerous mammals tend to be the smallest, including mice, rats and other rodents, and rabbits and hares. There are more house mice in the world than any other single mammal, except humans.
Rodents There are more species of rodent in the world than all other mammals put together.
Altogether, there are some 1800 kinds. What makes them different from other small mammals is their strong teeth. All rodents have two pairs of razor-sharp front teeth for gnawing nuts and berries and a set of ridged teeth in their cheeks for chewing. Like fingernails, the pairs of front teeth, called incisors, grow all the time. Only constant gnawing keeps them the same length.