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. Arborial mammals live in trees an example of this is in monkeys. Most arborial animals are either brachiating, or scansorial.