Mammals are a class of animals that have some distinct characteristics (though there are always exceptions).
The main mammalian characteristics are:
- Endothermic– body temperature is controlled by internal processes. Sweating, panting to cool down, goosebumps, shivering to warm up.
- Fur/hair– some mammals are absolutely covered in fur while others seem to have none, such as dolphins and whales.
- Mammary glands– females produce milk for their young.
- Three middle ear bones– birds and reptiles only have one bone.
- Neocortex– an area of the brain that is used for sensory perception, motor commands, spatial reasoning, thought, and language.
Mammals can be divided into three main groups:
- The Placental Mammals– the most diverse group, with over 4,000 described species falling under here. Placental mammals all give birth to live young which have developed in the mother’s uterus and received nourishment from a specialize organ attached to the uterus, the placenta.
- The Marsupials– commonly thought of as the pouched mammals. They give live birth, however they give birth very early, and the underdeveloped embryo must climb up to the pouch where it will continues to develops for weeks or months. However, not all marsupials have pouches, such short-tailed opposums.
- The Monotremes– there are only 5 species of monotremes: the duck-billed platypus and five species of echidna. All are found in Australia and New Guinea. Monotremes are special because instead of giving birth to live young, they lay eggs. But once their young hatch, the females produce milk to nourish them.