Mammals are a class of vertebrate animals that are characterized by their warm-bloodedness, milk production for their young, and the presence of mammary glands. There are over 5,500 species of mammals in the world, ranging from small rodents to large whales. Mammals can be found on every continent except Antarctica, and they occupy a wide variety of habitats including forests, deserts, grasslands, and aquatic environments.
One of the most well-known characteristics of mammals is their ability to regulate their body temperature through the process of thermoregulation. This allows them to maintain a constant body temperature despite changes in their external environment. In addition to thermoregulation, mammals also have highly developed nervous systems and are generally considered to be more intelligent than other vertebrates. Many mammals have complex social structures and exhibit advanced behaviors such as tool use, problem solving, and communication through vocalizations or body language.