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? Gene expression patterns can be used to test hypotheses based on morphology. For example, the regulatory gene Bapx1 is expressed in the hinge of the developing lower jaw in fishes and reptiles. Where would you predict Bapx1 expression to occur in mammals?

Verified step by step guidance

1. Step 1: Understand the context of the problem. The question is about the evolutionary development of the mammalian ear, specifically the three tiny bones: the malleus, incus, and stapes. These bones are not present in reptiles like the T. rex.
2. Step 2: Consider the role of the Bapx1 gene. This gene is expressed in the hinge of the developing lower jaw in fishes and reptiles.
3. Step 3: Apply this knowledge to mammals. Given that the malleus, incus, and stapes are located near the hinge of the jaw in mammals, and that the Bapx1 gene is expressed in the hinge of the jaw in fishes and reptiles, it is reasonable to predict that Bapx1 expression would occur in the same area in mammals.
4. Step 4: Formulate your prediction. Based on the information provided, you would predict that Bapx1 expression occurs in the area near the hinge of the jaw in mammals, where the malleus, incus, and stapes are located.
5. Step 5: Remember that this is a prediction based on the available information. Further research and experimentation would be needed to confirm this prediction.