Final answer:
Mammals are characterized by traits such as hair or fur, mammary glands, a four-chambered heart, neocortex, and sweat glands. They are homeothermic and have heterodont dentition, often with a pentydactyl limb structure.
Step-by-step explanation:
All mammals share certain traits that define them as part of the class Mammalia. These traits include the presence of hair or fur, mammary glands used to nurse their young, a four-chambered heart, a brain covering called the neocortex, and sweat glands. Additionally, mammals are also characterized by the production of amniotic eggs, and they are endothermic, meaning they can regulate their body temperature internally.
Being homeothermic refers to an organism's ability to maintain a constant internal body temperature, regardless of external environmental changes. This trait is also known as being warm-blooded. Heterodont means an animal has different types of teeth adapted for different functions, such as incisors for cutting and molars for grinding. Pentydactyl refers to having five digits on each limb, which is a common trait among many mammalian species.