Defining Characteristics:
-Vertebrates
-Warm blooded (endotherm)
-Hair
-Lungs for breathing
-Live birth
-Produce milk

Fun Facts:
-Smallest- hog-nosed bat (0.05 ounces/1.4 grams)
-Largest- blue whale (150 tons/136 metric tons)
-Number of Species Worldwide- more than 4,000