Around 800,000 are recognized as belonging to the animal kingdom. Nearly 5000 of those are mammals. A scientist who specializes in the study of these animals is called a mammalogist. Survival of a species depends upon environmental conditions that provide life-sustaining elements. Mammals also rely on maternal instincts, habits and behavior that produce offspring and maintain the species.
Mammals are the true mothers of nature.
One well-known characteristic that separates the class of mammals from other animals is the mammary glands. Found only in mammals, these glands produce milk or a milk-like liquid. All mammals feed their young through the process of lactation. Milk-producing creatures have noteworthy differences that divide them into more specific categories. Eutherian, or placental, is one infraclass of mammals.