Monotremes

The monotremes is the oldest class of animals still alive. Members of this group are egg layers as well as share primitive skeletal traits with other living mammals, such as the shoulder girdle and skull characteristics.

When compared to more common mammalian kinds, monotremes have anatomical differences in their brains, jaws, digestive tract, reproductive tract, and other body parts. Furthermore, rather than bearing live young, female monotremes lay eggs, yet, like all mammals, they nurse their young with milk. Monotremes, like other mammals, have a fast metabolic rate, hair on their body, milk produced by mammary glands to nourish their young, a single bone in their lower jaw, and three middle-ear bones.

The platypus and echidna are the only monotreme species still in existence. They can be found only in Australia and New Guinea (an island not far from Australia). The monotremes mother carries the eggs inside her body for a long time to supply nutrition. She deposits the eggs in a nest or den, and the chicks hatch after about ten days. When the pups, known as "puggles," hatch, they are undeveloped, similar to newborn marsupials. Monotremes feed their young with milk, unlike other egg layers. They excrete milk through glands in their skin rather than a nipple or teat.