Mammals share at least three characteristics not found in other animals. Three middle ear bones, hair, and the production of milk by modified sweat glands called mammary glands. The three middle ear bones, the malleus, incus, and stapes function in the transmission of vibrations from the tympanic membrane/eardrum to the inner ear. The malleus and incus are derived from bones present in the lower jaw of mammalian ancestors. Mammalian hair is present in all mammals at some point in their development. Hair has several functions, including insulation, color patterning, and aiding in the sense of touch. All female mammals produce milk from their mammary glands in order to nourish newborn offspring. The female mammals invest a great deal of energy caring for each of their offspring, a situation which has important ramifications in many aspects of mammalian evolution, ecology, and behavior.
They have adapted to survive and to move around in their chosen habitat. As many need to find, food, shelter, and the breeding mates. They have to be able to quickly move through the environment before any of the carnivores try to get them. With the mammals in the ocean they have developed flippers instead of legs so they could glide and swim through the water to search for prey, and to make speedy escapes so the wont get preyed on.
There are nineteen divisions of mammals. The Order of division for mammals are Artiodactyla, Carnivora, Cetacea, chiroptera, Dermoptera, Edentata, Hyracoidae, Insectivora, Lagomorpha, Marsupialia, *Monotremata, Perissodactyla, Pholidata, Pinnipedia, Primates, Proboscidea, rodentia, Sirenia, Tubulidentata.
I chose the family insectivores. Most insectivores are small; shrews, for example, are among the smallest mammals. Most rely more on their senses of hearing, smell, and touch than on vision. Some shrews can echolocate. The part of the brain that houses the sense of smell is especially well developed. The ear region of insectivores lacks an ossified bulla.
I chose the genus common dolphin. Both common dolphin species are medium-sized; adults range between 1.9 and 2.5 m (6.2 and 8.2 ft) long, and can weigh between 80 and 235 kg (176 and 518 lb), although the range between 80 and 150 kg (180 and 330 lb) is more common. Males are generally longer and heavier. The color pattern on the body is unusual. The back is dark and the belly is white, while on each side is an hourglass pattern colored light grey, yellow, or gold in front and dirty grey in back. They have long, thin rostra with up to 50–60 small, sharp, interlocking teeth on each side of each jaw.