What shared biological trait is immediately recognizable for all members of Class Mammalia?

Answer

The ability to produce milk to nourish their young

Key defining characteristics of the Class Mammalia include the presence of hair or fur and the physiological ability to lactate to feed offspring. Mammals are also warm-blooded.

What shared biological trait is immediately recognizable for all members of Class Mammalia?
taxonomyclassificationDogbreedGerman Shepherd