The size and shape of the vertebrate skull can reveal a great deal about an animal's lifestyle and evolutionary relationships. Consider your own skull. If you put your finger in your ear and move your jaw up and down, you can feel the space near the hinge of your jaw. Nestled in this space are the tiny bones that make your hearing possible: the malleus, incus, and stapes. All mammals have these three ear bones, but reptiles such as this T. rex don't. Where did ear bones come from? How is the opossum related to you? Select True or False for each statement. T/F An opossum is an animal, but I am a human. T/F An opossum is a mammal, but I am a human. T/F An opossum is a marsupial, but I am a placental mammal. T/F The opossum and I are both tetrapods.