What makes an animal a mammal? And what is not a mammal? Mammals have skeletons as deer have, breathe air in lungs as whales do, and are born alive as are calves. What is not a mammal? A ladybug has no skeleton, a fish breathes through gills and a bird hatches from an egg. Monkeys, dolphins, and elephants are mammals—and so are you and I! With clear, simple language, beautiful paintings, a chart, diagrams, and a cutaway, acclaimed author-illustrator Lizzy Rockwell has created a beautiful and informative book that introduces young children to animal classification and dichotomous inquiry.