Bipartite and duplex uteran systems give room for a larger litter size, where as a simplex uterus, or a bicornate uterus provides for smaller litters. The longest mammal gestation is in an elephant which is two years, while the shortest is in hamsters, whose gestation is only two days. The factors of gestation length are the size of the animal, and its development at birth. There are two ways of describing the course of development in newborn mammals. Mammals can be altricial, meaning they are poorly developed at birth, or mammals can be precocial, meaning they are well developed at birth.
Mammals are very diverse, and therefore exhibit many different kinds of locomotion.
Kangaroos are saltorial. Fossorial mammals crawl underground like moles. Semi-aquatic mammals live half of their life on land, and the other half in the water like beavers. Aquatic mammals spend their entire life in water. Whales are aquatic.