Mammals, Monotremes and Marsupials
Mammalian Characteristics and the Diversity of Mammals
Aug 20, 2009
Although only about 4600 species of mammals exist, they show incredible diversity in size and shape. The largest mammal is the blue whale and even this huge animal shares characteristics with a tiny mouse. Mammals occupy many different places on Earth from the Arctic to the African desert.
Mammalian Characteristics
All mammals have hair somewhere on their body. In most cases, hair provides insulation in the form of a furry coat, but some mammals appear naked of hair. They do have hair somewhere; it may not be clearly visible on some mammals. On whales and dolphins for example, hair has been reduced to several thick bristles rather than a full coat.
Mammals are warm-blooded animals, which allows them to keep their body temperatures constant. It also means they can live in almost any environment because they can regulate their temperature according to surrounding environment. If it is cold, they generate heat and if the environment is hot, they sweat to cool down, depending on their needs.
The word mammal is derived from the words mammary glands, and all female mammals have them.
Mammalian Habitats
Mammals inhabit all sorts of places and are the most widespread of the animal groups. Mammals breathe air via lungs but this doesn’t prevent some mammals living in water. Dolphins and whales, while streamlined and adapted to water just like a shark or fish, still come up for air, breathing in through a large nostril or blowhole on the top of the head.
Other mammals, such as the camel, have adaptations for walking on sand and enduring high temperatures, while in contrast, a polar bear lives in the Arctic, wandering snow covered grounds and dealing with extreme cold.
What is a Monotreme?
Quite simply, a monotreme is a small group of mammals that lay young inside of eggs; they are two species of echidna and the duck-billed platypus. They lay eggs similar to birds or reptiles, except that the monotreme eggs are much softer.
Young hatch after a few days and continue to grow as the mother nurses them. Echidnas have a pouch on their underside where they keep their young and the platypus keep their young in an underground nest. Monotremes feed their young milk just like other mammals; however, they don’t have teats. Instead they secrete milk onto their fur for the young to lap up.
What is a Marsupial?
Marsupials are a larger group than monotremes but still small when compared to placental mammals. Most marsupials are found in Australia and New Guinea, and a few species are found in America.
While the placental mammal uterus expands as the fetus grows, the marsupial uterus cannot expand so young are born live but continue their development inside the mother’s pouch. Once outside the birth canal, young must make their way through the mother’s fur to find her nipples.
Often the mother’s nipples are inside the pouch and the baby will spend several months inside until it is well developed and can leave the pouch. Often they return to the pouch to feed or sleep for several more months until they are fully developed and too large for the pouch.
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