Besides possessing hair or fur, what other two key shared characteristics define the Class Mammalia?

Production of milk via mammary glands and being warm-blooded (endothermic)

The classification of woodrats into the Class Mammalia is supported by three fundamental biological traits common to all members of this class. While the presence of hair or fur is a recognized characteristic, the other two essential defining features are the physiological ability to nourish their young via milk produced by specialized mammary glands, and the mechanism of thermoregulation known as being warm-blooded, or endothermic. These traits enable mammals, including woodrats, to maintain stable internal body temperatures, facilitating survival across the diverse and often challenging habitats, such as arid deserts or high-elevation forests, where woodrats are found.