While mammals differ in sizes and skeletal structures, all share similar physical traits. They can live in a variety of habitats, but all mammals must be able to breath air, even marine mammals such as dolphins, whales and manatees. Humans, who are also mammals, share the same characteristics as most other mammal species.
Body Temperature Control
All mammals are warm-blooded animals able to keep their bodies at a constant temperature by controlling their own body heat. This is contrary to cold-blooded animals, which rely on an outside source like the sun to warm their bodies. Mammals are also the only animals that can sweat to cool themselves. Mammals must eat more food than cold-blooded animals to produce the necessary energy for body temperature control.
Also referred to as "fur," hair is only found on mammals. All land and marine mammals have some amount of fur on their bodies at some point in their lives. The primary function of hair is to provide warmth for mammals in cold temperatures such as bears and foxes. Desert-dwelling mammals like camels and jackrabbits use fur to prevent excessive heat on their skin. Mammalian hair grows from pores in the skin called follicles; the root of the hair is lodged within the pore. Each mammal also has varying melanins, a group of proteins that determine the colour of the hair.
The vast majority of mammals give live birth to their young. The amount of time an animal is pregnant varies among mammal species. Human females carry a child for eight to nine months. In 2010, researchers from Durham University and the University of Reading in England revealed the length of a mammal gestation period correlates with the structure of the female's placenta. Small rodents and rabbits may give birth in less than a month, while larger mammals such as rhinoceroses and elephants may carry a baby for 1 1/2 years. Exceptions to the life-birth rule are the duck-billed platypus and echidna. They are mammals, but they eggs for reproduction.
All female mammals have the capability of breastfeeding. Mammary glands are organs within female mammals that secretes milk. These glands are highly modified sweat glands. Growth hormones and prolactin hormones stimulate the formation of milk. Once the milk is created, it travels from the gland through ducts to the mammals' teats. The amount of teats on a mammal varies between species.